diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 73ef633955209..36fbbeb2ec74b 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -158,7 +158,7 @@ namespace ts {
          * If so, the node _must_ be in the current file (as that's the only way anything could have traversed to it to yield it as the error node)
          * This version of `createDiagnosticForNode` uses the binder's context to account for this, and always yields correct diagnostics even in these situations.
          */
-        function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
+        function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): DiagnosticWithLocation {
             return createDiagnosticForNodeInSourceFile(getSourceFileOfNode(node) || file, node, message, arg0, arg1, arg2);
         }
 
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 8f7a54089bcbc..b7f31d46728a4 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -313,11 +313,11 @@ namespace ts {
 
             getSuggestionDiagnostics: file => {
                 return (suggestionDiagnostics.get(file.fileName) || emptyArray).concat(getUnusedDiagnostics());
-                function getUnusedDiagnostics(): ReadonlyArray<Diagnostic> {
+                function getUnusedDiagnostics(): ReadonlyArray<DiagnosticWithLocation> {
                     if (file.isDeclarationFile) return emptyArray;
 
                     checkSourceFile(file);
-                    const diagnostics: Diagnostic[] = [];
+                    const diagnostics: DiagnosticWithLocation[] = [];
                     Debug.assert(!!(getNodeLinks(file).flags & NodeCheckFlags.TypeChecked));
                     checkUnusedIdentifiers(getPotentiallyUnusedIdentifiers(file), (kind, diag) => {
                         if (!unusedIsError(kind)) {
@@ -481,7 +481,7 @@ namespace ts {
 
         const diagnostics = createDiagnosticCollection();
         // Suggestion diagnostics must have a file. Keyed by source file name.
-        const suggestionDiagnostics = createMultiMap<Diagnostic>();
+        const suggestionDiagnostics = createMultiMap<DiagnosticWithLocation>();
 
         const enum TypeFacts {
             None = 0,
@@ -628,7 +628,7 @@ namespace ts {
             Local,
             Parameter,
         }
-        type AddUnusedDiagnostic = (type: UnusedKind, diagnostic: Diagnostic) => void;
+        type AddUnusedDiagnostic = (type: UnusedKind, diagnostic: DiagnosticWithLocation) => void;
 
         const builtinGlobals = createSymbolTable();
         builtinGlobals.set(undefinedSymbol.escapedName, undefinedSymbol);
@@ -824,7 +824,7 @@ namespace ts {
             diagnostics.add(diagnostic);
         }
 
-        function addErrorOrSuggestion(isError: boolean, diagnostic: Diagnostic) {
+        function addErrorOrSuggestion(isError: boolean, diagnostic: DiagnosticWithLocation) {
             if (isError) {
                 diagnostics.add(diagnostic);
             }
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 7f03ba06b1139..5307c1de7b470 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -14,8 +14,8 @@ namespace ts {
         return pathIsRelative(moduleName) || isRootedDiskPath(moduleName);
     }
 
-    export function sortAndDeduplicateDiagnostics(diagnostics: ReadonlyArray<Diagnostic>): Diagnostic[] {
-        return sortAndDeduplicate(diagnostics, compareDiagnostics);
+    export function sortAndDeduplicateDiagnostics<T extends Diagnostic>(diagnostics: ReadonlyArray<T>): T[] {
+        return sortAndDeduplicate<T>(diagnostics, compareDiagnostics);
     }
 }
 
@@ -1619,8 +1619,8 @@ namespace ts {
         return localizedDiagnosticMessages && localizedDiagnosticMessages[message.key] || message.message;
     }
 
-    export function createFileDiagnostic(file: SourceFile, start: number, length: number, message: DiagnosticMessage, ...args: (string | number)[]): Diagnostic;
-    export function createFileDiagnostic(file: SourceFile, start: number, length: number, message: DiagnosticMessage): Diagnostic {
+    export function createFileDiagnostic(file: SourceFile, start: number, length: number, message: DiagnosticMessage, ...args: (string | number)[]): DiagnosticWithLocation;
+    export function createFileDiagnostic(file: SourceFile, start: number, length: number, message: DiagnosticMessage): DiagnosticWithLocation {
         Debug.assertGreaterThanOrEqual(start, 0);
         Debug.assertGreaterThanOrEqual(length, 0);
 
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index e9c0ca66f1d8c..975331e715366 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -595,7 +595,7 @@ namespace ts {
         // tslint:enable variable-name
 
         let sourceFile: SourceFile;
-        let parseDiagnostics: Diagnostic[];
+        let parseDiagnostics: DiagnosticWithLocation[];
         let syntaxCursor: IncrementalParser.SyntaxCursor;
 
         let currentToken: SyntaxKind;
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 365e948f749e4..c453080f3bf9b 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -394,8 +394,8 @@ namespace ts {
         return resolutions;
     }
 
-    interface DiagnosticCache {
-        perFile?: Map<Diagnostic[]>;
+    interface DiagnosticCache<T extends Diagnostic> {
+        perFile?: Map<T[]>;
         allDiagnostics?: Diagnostic[];
     }
 
@@ -454,7 +454,7 @@ namespace ts {
 
     export function getConfigFileParsingDiagnostics(configFileParseResult: ParsedCommandLine): ReadonlyArray<Diagnostic> {
         return configFileParseResult.options.configFile ?
-            configFileParseResult.options.configFile.parseDiagnostics.concat(configFileParseResult.errors) :
+            [...configFileParseResult.options.configFile.parseDiagnostics, ...configFileParseResult.errors] :
             configFileParseResult.errors;
     }
 
@@ -517,8 +517,8 @@ namespace ts {
         let classifiableNames: UnderscoreEscapedMap<true>;
         let modifiedFilePaths: Path[] | undefined;
 
-        const cachedSemanticDiagnosticsForFile: DiagnosticCache = {};
-        const cachedDeclarationDiagnosticsForFile: DiagnosticCache = {};
+        const cachedSemanticDiagnosticsForFile: DiagnosticCache<Diagnostic> = {};
+        const cachedDeclarationDiagnosticsForFile: DiagnosticCache<DiagnosticWithLocation> = {};
 
         let resolvedTypeReferenceDirectives = createMap<ResolvedTypeReferenceDirective>();
         let fileProcessingDiagnostics = createDiagnosticCollection();
@@ -1313,10 +1313,10 @@ namespace ts {
             return filesByName.get(path);
         }
 
-        function getDiagnosticsHelper(
+        function getDiagnosticsHelper<T extends Diagnostic>(
             sourceFile: SourceFile,
-            getDiagnostics: (sourceFile: SourceFile, cancellationToken: CancellationToken) => ReadonlyArray<Diagnostic>,
-            cancellationToken: CancellationToken): ReadonlyArray<Diagnostic> {
+            getDiagnostics: (sourceFile: SourceFile, cancellationToken: CancellationToken) => ReadonlyArray<T>,
+            cancellationToken: CancellationToken): ReadonlyArray<T> {
             if (sourceFile) {
                 return getDiagnostics(sourceFile, cancellationToken);
             }
@@ -1328,7 +1328,7 @@ namespace ts {
             }));
         }
 
-        function getSyntacticDiagnostics(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<Diagnostic> {
+        function getSyntacticDiagnostics(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<DiagnosticWithLocation> {
             return getDiagnosticsHelper(sourceFile, getSyntacticDiagnosticsForFile, cancellationToken);
         }
 
@@ -1336,7 +1336,7 @@ namespace ts {
             return getDiagnosticsHelper(sourceFile, getSemanticDiagnosticsForFile, cancellationToken);
         }
 
-        function getDeclarationDiagnostics(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<Diagnostic> {
+        function getDeclarationDiagnostics(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<DiagnosticWithLocation> {
             const options = program.getCompilerOptions();
             // collect diagnostics from the program only once if either no source file was specified or out/outFile is set (bundled emit)
             if (!sourceFile || options.out || options.outFile) {
@@ -1347,7 +1347,7 @@ namespace ts {
             }
         }
 
-        function getSyntacticDiagnosticsForFile(sourceFile: SourceFile): ReadonlyArray<Diagnostic> {
+        function getSyntacticDiagnosticsForFile(sourceFile: SourceFile): ReadonlyArray<DiagnosticWithLocation> {
             // For JavaScript files, we report semantic errors for using TypeScript-only
             // constructs from within a JavaScript file as syntactic errors.
             if (isSourceFileJavaScript(sourceFile)) {
@@ -1382,7 +1382,7 @@ namespace ts {
             }
         }
 
-        function getSemanticDiagnosticsForFile(sourceFile: SourceFile, cancellationToken: CancellationToken): Diagnostic[] {
+        function getSemanticDiagnosticsForFile(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<Diagnostic> {
             return getAndCacheDiagnostics(sourceFile, cancellationToken, cachedSemanticDiagnosticsForFile, getSemanticDiagnosticsForFileNoCache);
         }
 
@@ -1403,15 +1403,22 @@ namespace ts {
                 // By default, only type-check .ts, .tsx, 'Deferred' and 'External' files (external files are added by plugins)
                 const includeBindAndCheckDiagnostics = sourceFile.scriptKind === ScriptKind.TS || sourceFile.scriptKind === ScriptKind.TSX ||
                     sourceFile.scriptKind === ScriptKind.External || isCheckJs || sourceFile.scriptKind === ScriptKind.Deferred;
-                const bindDiagnostics = includeBindAndCheckDiagnostics ? sourceFile.bindDiagnostics : emptyArray;
+                const bindDiagnostics: ReadonlyArray<Diagnostic> = includeBindAndCheckDiagnostics ? sourceFile.bindDiagnostics : emptyArray;
                 const checkDiagnostics = includeBindAndCheckDiagnostics ? typeChecker.getDiagnostics(sourceFile, cancellationToken) : emptyArray;
                 const fileProcessingDiagnosticsInFile = fileProcessingDiagnostics.getDiagnostics(sourceFile.fileName);
                 const programDiagnosticsInFile = programDiagnostics.getDiagnostics(sourceFile.fileName);
-                let diagnostics = bindDiagnostics.concat(checkDiagnostics, fileProcessingDiagnosticsInFile, programDiagnosticsInFile);
-                if (isCheckJs) {
-                    diagnostics = concatenate(diagnostics, sourceFile.jsDocDiagnostics);
+
+                let diagnostics: Diagnostic[] | undefined;
+                for (const diags of [bindDiagnostics, checkDiagnostics, fileProcessingDiagnosticsInFile, programDiagnosticsInFile, isCheckJs ? sourceFile.jsDocDiagnostics : undefined]) {
+                    if (diags) {
+                        for (const diag of diags) {
+                            if (shouldReportDiagnostic(diag)) {
+                                diagnostics = append(diagnostics, diag);
+                            }
+                        }
+                    }
                 }
-                return filter(diagnostics, shouldReportDiagnostic);
+                return diagnostics;
             });
         }
 
@@ -1440,9 +1447,9 @@ namespace ts {
             return true;
         }
 
-        function getJavaScriptSyntacticDiagnosticsForFile(sourceFile: SourceFile): Diagnostic[] {
+        function getJavaScriptSyntacticDiagnosticsForFile(sourceFile: SourceFile): DiagnosticWithLocation[] {
             return runWithCancellationToken(() => {
-                const diagnostics: Diagnostic[] = [];
+                const diagnostics: DiagnosticWithLocation[] = [];
                 let parent: Node = sourceFile;
                 walk(sourceFile);
 
@@ -1610,20 +1617,20 @@ namespace ts {
                     }
                 }
 
-                function createDiagnosticForNodeArray(nodes: NodeArray<Node>, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
+                function createDiagnosticForNodeArray(nodes: NodeArray<Node>, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): DiagnosticWithLocation {
                     const start = nodes.pos;
                     return createFileDiagnostic(sourceFile, start, nodes.end - start, message, arg0, arg1, arg2);
                 }
 
                 // Since these are syntactic diagnostics, parent might not have been set
                 // this means the sourceFile cannot be infered from the node
-                function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): Diagnostic {
+                function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number): DiagnosticWithLocation {
                     return createDiagnosticForNodeInSourceFile(sourceFile, node, message, arg0, arg1, arg2);
                 }
             });
         }
 
-        function getDeclarationDiagnosticsWorker(sourceFile: SourceFile | undefined, cancellationToken: CancellationToken): Diagnostic[] {
+        function getDeclarationDiagnosticsWorker(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<DiagnosticWithLocation> {
             return getAndCacheDiagnostics(sourceFile, cancellationToken, cachedDeclarationDiagnosticsForFile, getDeclarationDiagnosticsForFileNoCache);
         }
 
@@ -1635,15 +1642,16 @@ namespace ts {
             });
         }
 
-        function getAndCacheDiagnostics(
+        function getAndCacheDiagnostics<T extends Diagnostic>(
             sourceFile: SourceFile | undefined,
             cancellationToken: CancellationToken,
-            cache: DiagnosticCache,
-            getDiagnostics: (sourceFile: SourceFile, cancellationToken: CancellationToken) => Diagnostic[]) {
+            cache: DiagnosticCache<T>,
+            getDiagnostics: (sourceFile: SourceFile, cancellationToken: CancellationToken) => T[],
+        ): ReadonlyArray<T> {
 
             const cachedResult = sourceFile
                 ? cache.perFile && cache.perFile.get(sourceFile.path)
-                : cache.allDiagnostics;
+                : cache.allDiagnostics as T[];
 
             if (cachedResult) {
                 return cachedResult;
@@ -1651,7 +1659,7 @@ namespace ts {
             const result = getDiagnostics(sourceFile, cancellationToken) || emptyArray;
             if (sourceFile) {
                 if (!cache.perFile) {
-                    cache.perFile = createMap<Diagnostic[]>();
+                    cache.perFile = createMap<T[]>();
                 }
                 cache.perFile.set(sourceFile.path, result);
             }
@@ -1661,7 +1669,7 @@ namespace ts {
             return result;
         }
 
-        function getDeclarationDiagnosticsForFile(sourceFile: SourceFile, cancellationToken: CancellationToken): Diagnostic[] {
+        function getDeclarationDiagnosticsForFile(sourceFile: SourceFile, cancellationToken: CancellationToken): ReadonlyArray<DiagnosticWithLocation> {
             return sourceFile.isDeclarationFile ? [] : getDeclarationDiagnosticsWorker(sourceFile, cancellationToken);
         }
 
diff --git a/src/compiler/transformer.ts b/src/compiler/transformer.ts
index 16a6912757f40..b661120b961a6 100644
--- a/src/compiler/transformer.ts
+++ b/src/compiler/transformer.ts
@@ -90,7 +90,7 @@ namespace ts {
         let onSubstituteNode: TransformationContext["onSubstituteNode"] = (_, node) => node;
         let onEmitNode: TransformationContext["onEmitNode"] = (hint, node, callback) => callback(hint, node);
         let state = TransformationState.Uninitialized;
-        const diagnostics: Diagnostic[] = [];
+        const diagnostics: DiagnosticWithLocation[] = [];
 
         // The transformation context is provided to each transformer as part of transformer
         // initialization.
diff --git a/src/compiler/transformers/declarations.ts b/src/compiler/transformers/declarations.ts
index 346f1343fabce..953f8279def76 100644
--- a/src/compiler/transformers/declarations.ts
+++ b/src/compiler/transformers/declarations.ts
@@ -1,6 +1,6 @@
 /*@internal*/
 namespace ts {
-    export function getDeclarationDiagnostics(host: EmitHost, resolver: EmitResolver, file: SourceFile | undefined): Diagnostic[] {
+    export function getDeclarationDiagnostics(host: EmitHost, resolver: EmitResolver, file: SourceFile | undefined): DiagnosticWithLocation[] {
         if (file && isSourceFileJavaScript(file)) {
             return []; // No declaration diagnostics for js for now
         }
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 23e990d913e70..44c5ddb5d5034 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2599,17 +2599,17 @@ namespace ts {
 
         // File-level diagnostics reported by the parser (includes diagnostics about /// references
         // as well as code diagnostics).
-        /* @internal */ parseDiagnostics: Diagnostic[];
+        /* @internal */ parseDiagnostics: DiagnosticWithLocation[];
 
         // File-level diagnostics reported by the binder.
-        /* @internal */ bindDiagnostics: Diagnostic[];
-        /* @internal */ bindSuggestionDiagnostics?: Diagnostic[];
+        /* @internal */ bindDiagnostics: DiagnosticWithLocation[];
+        /* @internal */ bindSuggestionDiagnostics?: DiagnosticWithLocation[];
 
         // File-level JSDoc diagnostics reported by the JSDoc parser
-        /* @internal */ jsDocDiagnostics?: Diagnostic[];
+        /* @internal */ jsDocDiagnostics?: DiagnosticWithLocation[];
 
         // Stores additional file-level diagnostics reported by the program
-        /* @internal */ additionalSyntacticDiagnostics?: ReadonlyArray<Diagnostic>;
+        /* @internal */ additionalSyntacticDiagnostics?: ReadonlyArray<DiagnosticWithLocation>;
 
         // Stores a line map for the file.
         // This field should never be used directly to obtain line map, use getLineMap function instead.
@@ -2747,9 +2747,10 @@ namespace ts {
 
         getOptionsDiagnostics(cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
         getGlobalDiagnostics(cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
-        getSyntacticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
+        getSyntacticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<DiagnosticWithLocation>;
+        /** The first time this is called, it will return global diagnostics (no location). */
         getSemanticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
-        getDeclarationDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
+        getDeclarationDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<DiagnosticWithLocation>;
         getConfigFileParsingDiagnostics(): ReadonlyArray<Diagnostic>;
 
         /**
@@ -3070,7 +3071,7 @@ namespace ts {
          * Does *not* get *all* suggestion diagnostics, just the ones that were convenient to report in the checker.
          * Others are added in computeSuggestionDiagnostics.
          */
-        /* @internal */ getSuggestionDiagnostics(file: SourceFile): ReadonlyArray<Diagnostic>;
+        /* @internal */ getSuggestionDiagnostics(file: SourceFile): ReadonlyArray<DiagnosticWithLocation>;
 
         /**
          * Depending on the operation performed, it may be appropriate to throw away the checker
@@ -4228,6 +4229,11 @@ namespace ts {
         code: number;
         source?: string;
     }
+    export interface DiagnosticWithLocation extends Diagnostic {
+        file: SourceFile;
+        start: number;
+        length: number;
+    }
 
     export enum DiagnosticCategory {
         Warning,
@@ -5084,7 +5090,7 @@ namespace ts {
          */
         onEmitNode: (hint: EmitHint, node: Node, emitCallback: (hint: EmitHint, node: Node) => void) => void;
 
-        /* @internal */ addDiagnostic(diag: Diagnostic): void;
+        /* @internal */ addDiagnostic(diag: DiagnosticWithLocation): void;
     }
 
     export interface TransformationResult<T extends Node> {
@@ -5092,7 +5098,7 @@ namespace ts {
         transformed: T[];
 
         /** Gets diagnostics for the transformation. */
-        diagnostics?: Diagnostic[];
+        diagnostics?: DiagnosticWithLocation[];
 
         /**
          * Gets a substitute for a node, if one is available; otherwise, returns the original node.
@@ -5310,7 +5316,8 @@ namespace ts {
 
         // If fileName is provided, gets all the diagnostics associated with that file name.
         // Otherwise, returns all the diagnostics (global and file associated) in this collection.
-        getDiagnostics(fileName?: string): Diagnostic[];
+        getDiagnostics(fileName: string): DiagnosticWithLocation[];
+        getDiagnostics(): Diagnostic[];
 
         reattachFileDiagnostics(newFile: SourceFile): void;
     }
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index df19a8948c722..64996153d23b6 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -603,7 +603,7 @@ namespace ts {
         }
     }
 
-    export function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): Diagnostic {
+    export function createDiagnosticForNode(node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): DiagnosticWithLocation {
         const sourceFile = getSourceFileOfNode(node);
         return createDiagnosticForNodeInSourceFile(sourceFile, node, message, arg0, arg1, arg2, arg3);
     }
@@ -613,17 +613,17 @@ namespace ts {
         return createFileDiagnostic(sourceFile, start, nodes.end - start, message, arg0, arg1, arg2, arg3);
     }
 
-    export function createDiagnosticForNodeInSourceFile(sourceFile: SourceFile, node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): Diagnostic {
+    export function createDiagnosticForNodeInSourceFile(sourceFile: SourceFile, node: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): DiagnosticWithLocation {
         const span = getErrorSpanForNode(sourceFile, node);
         return createFileDiagnostic(sourceFile, span.start, span.length, message, arg0, arg1, arg2, arg3);
     }
 
-    export function createDiagnosticForNodeSpan(sourceFile: SourceFile, startNode: Node, endNode: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): Diagnostic {
+    export function createDiagnosticForNodeSpan(sourceFile: SourceFile, startNode: Node, endNode: Node, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): DiagnosticWithLocation {
         const start = skipTrivia(sourceFile.text, startNode.pos);
         return createFileDiagnostic(sourceFile, start, endNode.end - start, message, arg0, arg1, arg2, arg3);
     }
 
-    export function createDiagnosticForNodeFromMessageChain(node: Node, messageChain: DiagnosticMessageChain): Diagnostic {
+    export function createDiagnosticForNodeFromMessageChain(node: Node, messageChain: DiagnosticMessageChain): DiagnosticWithLocation {
         const sourceFile = getSourceFileOfNode(node);
         const span = getErrorSpanForNode(sourceFile, node);
         return {
@@ -2645,7 +2645,7 @@ namespace ts {
     export function createDiagnosticCollection(): DiagnosticCollection {
         let nonFileDiagnostics = [] as SortedArray<Diagnostic>;
         const filesWithDiagnostics = [] as SortedArray<string>;
-        const fileDiagnostics = createMap<SortedArray<Diagnostic>>();
+        const fileDiagnostics = createMap<SortedArray<DiagnosticWithLocation>>();
         let hasReadNonFileDiagnostics = false;
 
         return {
@@ -2664,8 +2664,8 @@ namespace ts {
             if (diagnostic.file) {
                 diagnostics = fileDiagnostics.get(diagnostic.file.fileName);
                 if (!diagnostics) {
-                    diagnostics = [] as SortedArray<Diagnostic>;
-                    fileDiagnostics.set(diagnostic.file.fileName, diagnostics);
+                    diagnostics = [] as SortedArray<DiagnosticWithLocation>;
+                    fileDiagnostics.set(diagnostic.file.fileName, diagnostics as SortedArray<DiagnosticWithLocation>);
                     insertSorted(filesWithDiagnostics, diagnostic.file.fileName, compareStringsCaseSensitive);
                 }
             }
@@ -2687,12 +2687,14 @@ namespace ts {
             return nonFileDiagnostics;
         }
 
+        function getDiagnostics(fileName: string): DiagnosticWithLocation[];
+        function getDiagnostics(): Diagnostic[];
         function getDiagnostics(fileName?: string): Diagnostic[] {
             if (fileName) {
                 return fileDiagnostics.get(fileName) || [];
             }
 
-            const fileDiags = flatMap(filesWithDiagnostics, f => fileDiagnostics.get(f));
+            const fileDiags: Diagnostic[] = flatMap(filesWithDiagnostics, f => fileDiagnostics.get(f));
             if (!nonFileDiagnostics.length) {
                 return fileDiags;
             }
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 28233b797da47..96d7a01eaae68 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -1406,7 +1406,7 @@ namespace Harness {
             const dupeCase = ts.createMap<number>();
             for (const inputFile of inputFiles.filter(f => f.content !== undefined)) {
                 // Filter down to the errors in the file
-                const fileErrors = diagnostics.filter(e => {
+                const fileErrors = diagnostics.filter((e): e is ts.DiagnosticWithLocation => {
                     const errFn = e.file;
                     return errFn && utils.removeTestPathPrefixes(errFn.fileName) === utils.removeTestPathPrefixes(inputFile.unitName);
                 });
diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index 34d6f775a74b4..8c30f9411e671 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -398,13 +398,13 @@ namespace Harness.LanguageService {
         cleanupSemanticCache(): void {
             this.shim.cleanupSemanticCache();
         }
-        getSyntacticDiagnostics(fileName: string): ts.Diagnostic[] {
+        getSyntacticDiagnostics(fileName: string): ts.DiagnosticWithLocation[] {
             return unwrapJSONCallResult(this.shim.getSyntacticDiagnostics(fileName));
         }
-        getSemanticDiagnostics(fileName: string): ts.Diagnostic[] {
+        getSemanticDiagnostics(fileName: string): ts.DiagnosticWithLocation[] {
             return unwrapJSONCallResult(this.shim.getSemanticDiagnostics(fileName));
         }
-        getSuggestionDiagnostics(fileName: string): ts.Diagnostic[] {
+        getSuggestionDiagnostics(fileName: string): ts.DiagnosticWithLocation[] {
             return unwrapJSONCallResult(this.shim.getSuggestionDiagnostics(fileName));
         }
         getCompilerOptionsDiagnostics(): ts.Diagnostic[] {
diff --git a/src/harness/projectsRunner.ts b/src/harness/projectsRunner.ts
index 08e92a73be235..9ef536ad0c8be 100644
--- a/src/harness/projectsRunner.ts
+++ b/src/harness/projectsRunner.ts
@@ -154,7 +154,7 @@ namespace project {
                 const configParseResult = ts.parseJsonSourceFileConfigFileContent(result, configParseHost, ts.getDirectoryPath(configFileName), this.compilerOptions);
                 inputFiles = configParseResult.fileNames;
                 this.compilerOptions = configParseResult.options;
-                errors = result.parseDiagnostics.concat(configParseResult.errors);
+                errors = [...result.parseDiagnostics, ...configParseResult.errors];
             }
 
             const compilerHost = new ProjectCompilerHost(this.sys, this.compilerOptions, this.testCaseJustName, this.testCase, moduleKind);
diff --git a/src/server/client.ts b/src/server/client.ts
index a07e793dcba55..2a97a54a18dcc 100644
--- a/src/server/client.ts
+++ b/src/server/client.ts
@@ -346,21 +346,21 @@ namespace ts.server {
             return notImplemented();
         }
 
-        getSyntacticDiagnostics(file: string): Diagnostic[] {
+        getSyntacticDiagnostics(file: string): DiagnosticWithLocation[] {
             return this.getDiagnostics(file, CommandNames.SyntacticDiagnosticsSync);
         }
-        getSemanticDiagnostics(file: string): Diagnostic[] {
+        getSemanticDiagnostics(file: string): DiagnosticWithLocation[] {
             return this.getDiagnostics(file, CommandNames.SemanticDiagnosticsSync);
         }
-        getSuggestionDiagnostics(file: string): Diagnostic[] {
+        getSuggestionDiagnostics(file: string): DiagnosticWithLocation[] {
             return this.getDiagnostics(file, CommandNames.SuggestionDiagnosticsSync);
         }
 
-        private getDiagnostics(file: string, command: CommandNames): Diagnostic[] {
+        private getDiagnostics(file: string, command: CommandNames): DiagnosticWithLocation[] {
             const request = this.processRequest<protocol.SyntacticDiagnosticsSyncRequest | protocol.SemanticDiagnosticsSyncRequest | protocol.SuggestionDiagnosticsSyncRequest>(command, { file, includeLinePosition: true });
             const response = this.processResponse<protocol.SyntacticDiagnosticsSyncResponse | protocol.SemanticDiagnosticsSyncResponse | protocol.SuggestionDiagnosticsSyncResponse>(request);
 
-            return (<protocol.DiagnosticWithLinePosition[]>response.body).map((entry): Diagnostic => {
+            return (<protocol.DiagnosticWithLinePosition[]>response.body).map((entry): DiagnosticWithLocation => {
                 const category = firstDefined(Object.keys(DiagnosticCategory), id =>
                     isString(id) && entry.category === id.toLowerCase() ? (<any>DiagnosticCategory)[id] : undefined);
                 return {
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index bb3560cbde521..9f87bd150eccd 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -1329,7 +1329,7 @@ namespace ts.server {
             if (!result.endOfFileToken) {
                 result.endOfFileToken = <EndOfFileToken>{ kind: SyntaxKind.EndOfFileToken };
             }
-            const errors = result.parseDiagnostics;
+            const errors = result.parseDiagnostics as Diagnostic[];
             const parsedCommandLine = parseJsonSourceFileConfigFileContent(
                 result,
                 cachedDirectoryStructureHost,
diff --git a/src/services/codeFixProvider.ts b/src/services/codeFixProvider.ts
index 39f760ba04cf1..31b766d3bf5a3 100644
--- a/src/services/codeFixProvider.ts
+++ b/src/services/codeFixProvider.ts
@@ -79,17 +79,17 @@ namespace ts {
             return { fileName, textChanges };
         }
 
-        export function codeFixAll(context: CodeFixAllContext, errorCodes: number[], use: (changes: textChanges.ChangeTracker, error: Diagnostic, commands: Push<CodeActionCommand>) => void): CombinedCodeActions {
+        export function codeFixAll(context: CodeFixAllContext, errorCodes: number[], use: (changes: textChanges.ChangeTracker, error: DiagnosticWithLocation, commands: Push<CodeActionCommand>) => void): CombinedCodeActions {
             const commands: CodeActionCommand[] = [];
             const changes = textChanges.ChangeTracker.with(context, t =>
                 eachDiagnostic(context, errorCodes, diag => use(t, diag, commands)));
             return createCombinedCodeActions(changes, commands.length === 0 ? undefined : commands);
         }
 
-        function eachDiagnostic({ program, sourceFile }: CodeFixAllContext, errorCodes: number[], cb: (diag: Diagnostic) => void): void {
+        function eachDiagnostic({ program, sourceFile }: CodeFixAllContext, errorCodes: number[], cb: (diag: DiagnosticWithLocation) => void): void {
             for (const diag of program.getSemanticDiagnostics(sourceFile).concat(computeSuggestionDiagnostics(sourceFile, program))) {
                 if (contains(errorCodes, diag.code)) {
-                    cb(diag);
+                    cb(diag as DiagnosticWithLocation);
                 }
             }
         }
diff --git a/src/services/codefixes/addMissingInvocationForDecorator.ts b/src/services/codefixes/addMissingInvocationForDecorator.ts
index ead64f9a2ca9e..02b97eec37ebf 100644
--- a/src/services/codefixes/addMissingInvocationForDecorator.ts
+++ b/src/services/codefixes/addMissingInvocationForDecorator.ts
@@ -9,7 +9,7 @@ namespace ts.codefix {
             return [createCodeFixAction(fixId, changes, Diagnostics.Call_decorator_expression, fixId, Diagnostics.Add_to_all_uncalled_decorators)];
         },
         fixIds: [fixId],
-        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => makeChange(changes, diag.file!, diag.start!)),
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => makeChange(changes, diag.file, diag.start)),
     });
 
     function makeChange(changeTracker: textChanges.ChangeTracker, sourceFile: SourceFile, pos: number) {
diff --git a/src/services/codefixes/annotateWithTypeFromJSDoc.ts b/src/services/codefixes/annotateWithTypeFromJSDoc.ts
index 7b66467843650..b3fc09b7bc4b2 100644
--- a/src/services/codefixes/annotateWithTypeFromJSDoc.ts
+++ b/src/services/codefixes/annotateWithTypeFromJSDoc.ts
@@ -12,8 +12,8 @@ namespace ts.codefix {
         },
         fixIds: [fixId],
         getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
-            const decl = getDeclaration(diag.file!, diag.start!);
-            if (decl) doChange(changes, diag.file!, decl);
+            const decl = getDeclaration(diag.file, diag.start);
+            if (decl) doChange(changes, diag.file, decl);
         }),
     });
 
diff --git a/src/services/codefixes/disableJsDiagnostics.ts b/src/services/codefixes/disableJsDiagnostics.ts
index b5d3059dd42cb..c81446152dd05 100644
--- a/src/services/codefixes/disableJsDiagnostics.ts
+++ b/src/services/codefixes/disableJsDiagnostics.ts
@@ -38,8 +38,8 @@ namespace ts.codefix {
         getAllCodeActions: context => {
             const seenLines = createMap<true>();
             return codeFixAll(context, errorCodes, (changes, diag) => {
-                if (textChanges.isValidLocationToAddComment(diag.file!, diag.start!)) {
-                    makeChange(changes, diag.file!, diag.start!, seenLines);
+                if (textChanges.isValidLocationToAddComment(diag.file, diag.start)) {
+                    makeChange(changes, diag.file, diag.start, seenLines);
                 }
             });
         },
diff --git a/src/services/codefixes/fixAddMissingMember.ts b/src/services/codefixes/fixAddMissingMember.ts
index e53ce41ad8a75..c2a8316db379a 100644
--- a/src/services/codefixes/fixAddMissingMember.ts
+++ b/src/services/codefixes/fixAddMissingMember.ts
@@ -23,7 +23,7 @@ namespace ts.codefix {
             const seenNames = createMap<true>();
             return codeFixAll(context, errorCodes, (changes, diag) => {
                 const { program, preferences } = context;
-                const info = getInfo(diag.file!, diag.start!, program.getTypeChecker());
+                const info = getInfo(diag.file, diag.start, program.getTypeChecker());
                 if (!info) return;
                 const { classDeclaration, classDeclarationSourceFile, inJs, makeStatic, token, call } = info;
                 if (!addToSeen(seenNames, token.text)) {
diff --git a/src/services/codefixes/fixClassDoesntImplementInheritedAbstractMember.ts b/src/services/codefixes/fixClassDoesntImplementInheritedAbstractMember.ts
index a931f849cb235..d59df7a02b302 100644
--- a/src/services/codefixes/fixClassDoesntImplementInheritedAbstractMember.ts
+++ b/src/services/codefixes/fixClassDoesntImplementInheritedAbstractMember.ts
@@ -17,7 +17,7 @@ namespace ts.codefix {
         getAllCodeActions: context => {
             const seenClassDeclarations = createMap<true>();
             return codeFixAll(context, errorCodes, (changes, diag) => {
-                const classDeclaration = getClass(diag.file!, diag.start!);
+                const classDeclaration = getClass(diag.file, diag.start);
                 if (addToSeen(seenClassDeclarations, getNodeId(classDeclaration))) {
                     addMissingMembers(classDeclaration, context.sourceFile, context.program.getTypeChecker(), changes, context.preferences);
                 }
diff --git a/src/services/codefixes/fixClassIncorrectlyImplementsInterface.ts b/src/services/codefixes/fixClassIncorrectlyImplementsInterface.ts
index 4e0b5745149b4..0da45c46873dd 100644
--- a/src/services/codefixes/fixClassIncorrectlyImplementsInterface.ts
+++ b/src/services/codefixes/fixClassIncorrectlyImplementsInterface.ts
@@ -18,10 +18,10 @@ namespace ts.codefix {
         getAllCodeActions(context) {
             const seenClassDeclarations = createMap<true>();
             return codeFixAll(context, errorCodes, (changes, diag) => {
-                const classDeclaration = getClass(diag.file!, diag.start!);
+                const classDeclaration = getClass(diag.file, diag.start);
                 if (addToSeen(seenClassDeclarations, getNodeId(classDeclaration))) {
                     for (const implementedTypeNode of getClassImplementsHeritageClauseElements(classDeclaration)) {
-                        addMissingDeclarations(context.program.getTypeChecker(), implementedTypeNode, diag.file!, classDeclaration, changes, context.preferences);
+                        addMissingDeclarations(context.program.getTypeChecker(), implementedTypeNode, diag.file, classDeclaration, changes, context.preferences);
                     }
                 }
             });
diff --git a/src/services/codefixes/fixClassSuperMustPrecedeThisAccess.ts b/src/services/codefixes/fixClassSuperMustPrecedeThisAccess.ts
index af38b8e9025fd..2f7daf93dc735 100644
--- a/src/services/codefixes/fixClassSuperMustPrecedeThisAccess.ts
+++ b/src/services/codefixes/fixClassSuperMustPrecedeThisAccess.ts
@@ -17,7 +17,7 @@ namespace ts.codefix {
             const { sourceFile } = context;
             const seenClasses = createMap<true>(); // Ensure we only do this once per class.
             return codeFixAll(context, errorCodes, (changes, diag) => {
-                const nodes = getNodes(diag.file!, diag.start!);
+                const nodes = getNodes(diag.file, diag.start);
                 if (!nodes) return;
                 const { constructor, superCall } = nodes;
                 if (addToSeen(seenClasses, getNodeId(constructor.parent))) {
diff --git a/src/services/codefixes/fixConstructorForDerivedNeedSuperCall.ts b/src/services/codefixes/fixConstructorForDerivedNeedSuperCall.ts
index 2aed263ee833f..605bb660f0623 100644
--- a/src/services/codefixes/fixConstructorForDerivedNeedSuperCall.ts
+++ b/src/services/codefixes/fixConstructorForDerivedNeedSuperCall.ts
@@ -12,7 +12,7 @@ namespace ts.codefix {
         },
         fixIds: [fixId],
         getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) =>
-            doChange(changes, context.sourceFile, getNode(diag.file, diag.start!))),
+            doChange(changes, context.sourceFile, getNode(diag.file, diag.start))),
     });
 
     function getNode(sourceFile: SourceFile, pos: number): ConstructorDeclaration {
diff --git a/src/services/codefixes/fixExtendsInterfaceBecomesImplements.ts b/src/services/codefixes/fixExtendsInterfaceBecomesImplements.ts
index c3f406b847509..4320513fb617c 100644
--- a/src/services/codefixes/fixExtendsInterfaceBecomesImplements.ts
+++ b/src/services/codefixes/fixExtendsInterfaceBecomesImplements.ts
@@ -14,7 +14,7 @@ namespace ts.codefix {
         },
         fixIds: [fixId],
         getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
-            const nodes = getNodes(diag.file, diag.start!);
+            const nodes = getNodes(diag.file, diag.start);
             if (nodes) doChanges(changes, diag.file, nodes.extendsToken, nodes.heritageClauses);
         }),
     });
diff --git a/src/services/codefixes/fixForgottenThisPropertyAccess.ts b/src/services/codefixes/fixForgottenThisPropertyAccess.ts
index 31c6128d003f4..ce066277a27e2 100644
--- a/src/services/codefixes/fixForgottenThisPropertyAccess.ts
+++ b/src/services/codefixes/fixForgottenThisPropertyAccess.ts
@@ -19,7 +19,7 @@ namespace ts.codefix {
         },
         fixIds: [fixId],
         getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
-            doChange(changes, context.sourceFile, getInfo(diag.file, diag.start!, diag.code));
+            doChange(changes, context.sourceFile, getInfo(diag.file, diag.start, diag.code));
         }),
     });
 
diff --git a/src/services/codefixes/fixSpelling.ts b/src/services/codefixes/fixSpelling.ts
index 252b08b356af1..dbb23c3ac09dd 100644
--- a/src/services/codefixes/fixSpelling.ts
+++ b/src/services/codefixes/fixSpelling.ts
@@ -19,7 +19,7 @@ namespace ts.codefix {
         },
         fixIds: [fixId],
         getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
-            const info = getInfo(diag.file!, diag.start!, context);
+            const info = getInfo(diag.file, diag.start, context);
             const { target } = context.host.getCompilationSettings();
             if (info) doChange(changes, context.sourceFile, info.node, info.suggestion, target);
         }),
diff --git a/src/services/codefixes/fixUnusedIdentifier.ts b/src/services/codefixes/fixUnusedIdentifier.ts
index 148b42b1c7e61..6ba592ca2b8b5 100644
--- a/src/services/codefixes/fixUnusedIdentifier.ts
+++ b/src/services/codefixes/fixUnusedIdentifier.ts
@@ -53,7 +53,7 @@ namespace ts.codefix {
             return codeFixAll(context, errorCodes, (changes, diag) => {
                 const { sourceFile } = context;
                 const startToken = getTokenAtPosition(sourceFile, diag.start, /*includeJsDocComment*/ false);
-                const token = findPrecedingToken(textSpanEnd(diag), diag.file!);
+                const token = findPrecedingToken(textSpanEnd(diag), diag.file);
                 switch (context.fixId) {
                     case fixIdPrefix:
                         if (isIdentifier(token) && canPrefix(token)) {
@@ -62,7 +62,7 @@ namespace ts.codefix {
                         break;
                     case fixIdDelete:
                         // Ignore if this range was already deleted.
-                        if (deleted.some(d => rangeContainsPosition(d, diag.start!))) break;
+                        if (deleted.some(d => rangeContainsPosition(d, diag.start))) break;
 
                         const importDecl = tryGetFullImport(startToken);
                         if (importDecl) {
diff --git a/src/services/codefixes/useDefaultImport.ts b/src/services/codefixes/useDefaultImport.ts
index 99fc145b5630a..3fe451c41fb2a 100644
--- a/src/services/codefixes/useDefaultImport.ts
+++ b/src/services/codefixes/useDefaultImport.ts
@@ -13,8 +13,8 @@ namespace ts.codefix {
         },
         fixIds: [fixId],
         getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
-            const info = getInfo(diag.file!, diag.start!);
-            if (info) doChange(changes, diag.file!, info);
+            const info = getInfo(diag.file, diag.start);
+            if (info) doChange(changes, diag.file, info);
         }),
     });
 
diff --git a/src/services/formatting/formatting.ts b/src/services/formatting/formatting.ts
index 494a811c238de..b0273cc18e7a4 100644
--- a/src/services/formatting/formatting.ts
+++ b/src/services/formatting/formatting.ts
@@ -228,7 +228,7 @@ namespace ts.formatting {
      * This function will return a predicate that for a given text range will tell
      * if there are any parse errors that overlap with the range.
      */
-    function prepareRangeContainsErrorFunction(errors: Diagnostic[], originalRange: TextRange): (r: TextRange) => boolean {
+    function prepareRangeContainsErrorFunction(errors: ReadonlyArray<Diagnostic>, originalRange: TextRange): (r: TextRange) => boolean {
         if (!errors.length) {
             return rangeHasNoErrors;
         }
diff --git a/src/services/services.ts b/src/services/services.ts
index 9b8d0e0464899..0375f6fcf38f7 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -545,10 +545,10 @@ namespace ts {
         public referencedFiles: FileReference[];
         public typeReferenceDirectives: FileReference[];
 
-        public syntacticDiagnostics: Diagnostic[];
-        public parseDiagnostics: Diagnostic[];
-        public bindDiagnostics: Diagnostic[];
-        public bindSuggestionDiagnostics?: Diagnostic[];
+        public syntacticDiagnostics: DiagnosticWithLocation[];
+        public parseDiagnostics: DiagnosticWithLocation[];
+        public bindDiagnostics: DiagnosticWithLocation[];
+        public bindSuggestionDiagnostics?: DiagnosticWithLocation[];
 
         public isDeclarationFile: boolean;
         public isDefaultLib: boolean;
@@ -1377,7 +1377,7 @@ namespace ts {
         }
 
         /// Diagnostics
-        function getSyntacticDiagnostics(fileName: string): Diagnostic[] {
+        function getSyntacticDiagnostics(fileName: string): DiagnosticWithLocation[] {
             synchronizeHostData();
 
             return program.getSyntacticDiagnostics(getValidSourceFile(fileName), cancellationToken).slice();
@@ -1405,7 +1405,7 @@ namespace ts {
             return [...semanticDiagnostics, ...declarationDiagnostics];
         }
 
-        function getSuggestionDiagnostics(fileName: string): Diagnostic[] {
+        function getSuggestionDiagnostics(fileName: string): DiagnosticWithLocation[] {
             synchronizeHostData();
             return computeSuggestionDiagnostics(getValidSourceFile(fileName), program);
         }
diff --git a/src/services/shims.ts b/src/services/shims.ts
index c371533da0c1f..808da2eb1ec9c 100644
--- a/src/services/shims.ts
+++ b/src/services/shims.ts
@@ -1147,7 +1147,7 @@ namespace ts {
                         typeAcquisition: configFile.typeAcquisition,
                         files: configFile.fileNames,
                         raw: configFile.raw,
-                        errors: realizeDiagnostics(result.parseDiagnostics.concat(configFile.errors), "\r\n")
+                        errors: realizeDiagnostics([...result.parseDiagnostics, ...configFile.errors], "\r\n")
                     };
                 });
         }
diff --git a/src/services/suggestionDiagnostics.ts b/src/services/suggestionDiagnostics.ts
index 40ed7719c9fe4..c59c267d16448 100644
--- a/src/services/suggestionDiagnostics.ts
+++ b/src/services/suggestionDiagnostics.ts
@@ -1,9 +1,9 @@
 /* @internal */
 namespace ts {
-    export function computeSuggestionDiagnostics(sourceFile: SourceFile, program: Program): Diagnostic[] {
+    export function computeSuggestionDiagnostics(sourceFile: SourceFile, program: Program): DiagnosticWithLocation[] {
         program.getSemanticDiagnostics(sourceFile);
         const checker = program.getDiagnosticsProducingTypeChecker();
-        const diags: Diagnostic[] = [];
+        const diags: DiagnosticWithLocation[] = [];
 
         if (sourceFile.commonJsModuleIndicator &&
             (programContainsEs6Modules(program) || compilerOptionsIndicateEs6Modules(program.getCompilerOptions())) &&
diff --git a/src/services/transform.ts b/src/services/transform.ts
index 200fb9aacb249..b6b2a35708104 100644
--- a/src/services/transform.ts
+++ b/src/services/transform.ts
@@ -6,7 +6,7 @@ namespace ts {
      * @param compilerOptions Optional compiler options.
      */
     export function transform<T extends Node>(source: T | T[], transformers: TransformerFactory<T>[], compilerOptions?: CompilerOptions) {
-        const diagnostics: Diagnostic[] = [];
+        const diagnostics: DiagnosticWithLocation[] = [];
         compilerOptions = fixupCompilerOptions(compilerOptions, diagnostics);
         const nodes = isArray(source) ? source : [source];
         const result = transformNodes(/*resolver*/ undefined, /*emitHost*/ undefined, compilerOptions, nodes, transformers, /*allowDtsFiles*/ true);
diff --git a/src/services/types.ts b/src/services/types.ts
index b8e2c488b17cb..b1b0ccd6de885 100644
--- a/src/services/types.ts
+++ b/src/services/types.ts
@@ -249,9 +249,10 @@ namespace ts {
     export interface LanguageService {
         cleanupSemanticCache(): void;
 
-        getSyntacticDiagnostics(fileName: string): Diagnostic[];
+        getSyntacticDiagnostics(fileName: string): DiagnosticWithLocation[];
+        /** The first time this is called, it will return global diagnostics (no location). */
         getSemanticDiagnostics(fileName: string): Diagnostic[];
-        getSuggestionDiagnostics(fileName: string): Diagnostic[];
+        getSuggestionDiagnostics(fileName: string): DiagnosticWithLocation[];
 
         // TODO: Rename this to getProgramDiagnostics to better indicate that these are any
         // diagnostics present for the program level, and not just 'options' diagnostics.
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 40c3abdbb9e88..d2c66aede48d6 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -1734,9 +1734,10 @@ declare namespace ts {
         emit(targetSourceFile?: SourceFile, writeFile?: WriteFileCallback, cancellationToken?: CancellationToken, emitOnlyDtsFiles?: boolean, customTransformers?: CustomTransformers): EmitResult;
         getOptionsDiagnostics(cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
         getGlobalDiagnostics(cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
-        getSyntacticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
+        getSyntacticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<DiagnosticWithLocation>;
+        /** The first time this is called, it will return global diagnostics (no location). */
         getSemanticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
-        getDeclarationDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
+        getDeclarationDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<DiagnosticWithLocation>;
         getConfigFileParsingDiagnostics(): ReadonlyArray<Diagnostic>;
         /**
          * Gets a type checker that can be used to semantically analyze source files in the program.
@@ -2359,6 +2360,11 @@ declare namespace ts {
         code: number;
         source?: string;
     }
+    interface DiagnosticWithLocation extends Diagnostic {
+        file: SourceFile;
+        start: number;
+        length: number;
+    }
     enum DiagnosticCategory {
         Warning = 0,
         Error = 1,
@@ -2754,7 +2760,7 @@ declare namespace ts {
         /** Gets the transformed source files. */
         transformed: T[];
         /** Gets diagnostics for the transformation. */
-        diagnostics?: Diagnostic[];
+        diagnostics?: DiagnosticWithLocation[];
         /**
          * Gets a substitute for a node, if one is available; otherwise, returns the original node.
          *
@@ -2960,7 +2966,7 @@ declare namespace ts {
 }
 declare namespace ts {
     function isExternalModuleNameRelative(moduleName: string): boolean;
-    function sortAndDeduplicateDiagnostics(diagnostics: ReadonlyArray<Diagnostic>): Diagnostic[];
+    function sortAndDeduplicateDiagnostics<T extends Diagnostic>(diagnostics: ReadonlyArray<T>): T[];
 }
 declare function setTimeout(handler: (...args: any[]) => void, timeout: number): any;
 declare function clearTimeout(handle: any): void;
@@ -4497,9 +4503,10 @@ declare namespace ts {
     }
     interface LanguageService {
         cleanupSemanticCache(): void;
-        getSyntacticDiagnostics(fileName: string): Diagnostic[];
+        getSyntacticDiagnostics(fileName: string): DiagnosticWithLocation[];
+        /** The first time this is called, it will return global diagnostics (no location). */
         getSemanticDiagnostics(fileName: string): Diagnostic[];
-        getSuggestionDiagnostics(fileName: string): Diagnostic[];
+        getSuggestionDiagnostics(fileName: string): DiagnosticWithLocation[];
         getCompilerOptionsDiagnostics(): Diagnostic[];
         /**
          * @deprecated Use getEncodedSyntacticClassifications instead.
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 2324d24908bb1..71d598ca102e2 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -1734,9 +1734,10 @@ declare namespace ts {
         emit(targetSourceFile?: SourceFile, writeFile?: WriteFileCallback, cancellationToken?: CancellationToken, emitOnlyDtsFiles?: boolean, customTransformers?: CustomTransformers): EmitResult;
         getOptionsDiagnostics(cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
         getGlobalDiagnostics(cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
-        getSyntacticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
+        getSyntacticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<DiagnosticWithLocation>;
+        /** The first time this is called, it will return global diagnostics (no location). */
         getSemanticDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
-        getDeclarationDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
+        getDeclarationDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<DiagnosticWithLocation>;
         getConfigFileParsingDiagnostics(): ReadonlyArray<Diagnostic>;
         /**
          * Gets a type checker that can be used to semantically analyze source files in the program.
@@ -2359,6 +2360,11 @@ declare namespace ts {
         code: number;
         source?: string;
     }
+    interface DiagnosticWithLocation extends Diagnostic {
+        file: SourceFile;
+        start: number;
+        length: number;
+    }
     enum DiagnosticCategory {
         Warning = 0,
         Error = 1,
@@ -2754,7 +2760,7 @@ declare namespace ts {
         /** Gets the transformed source files. */
         transformed: T[];
         /** Gets diagnostics for the transformation. */
-        diagnostics?: Diagnostic[];
+        diagnostics?: DiagnosticWithLocation[];
         /**
          * Gets a substitute for a node, if one is available; otherwise, returns the original node.
          *
@@ -2960,7 +2966,7 @@ declare namespace ts {
 }
 declare namespace ts {
     function isExternalModuleNameRelative(moduleName: string): boolean;
-    function sortAndDeduplicateDiagnostics(diagnostics: ReadonlyArray<Diagnostic>): Diagnostic[];
+    function sortAndDeduplicateDiagnostics<T extends Diagnostic>(diagnostics: ReadonlyArray<T>): T[];
 }
 declare function setTimeout(handler: (...args: any[]) => void, timeout: number): any;
 declare function clearTimeout(handle: any): void;
@@ -4497,9 +4503,10 @@ declare namespace ts {
     }
     interface LanguageService {
         cleanupSemanticCache(): void;
-        getSyntacticDiagnostics(fileName: string): Diagnostic[];
+        getSyntacticDiagnostics(fileName: string): DiagnosticWithLocation[];
+        /** The first time this is called, it will return global diagnostics (no location). */
         getSemanticDiagnostics(fileName: string): Diagnostic[];
-        getSuggestionDiagnostics(fileName: string): Diagnostic[];
+        getSuggestionDiagnostics(fileName: string): DiagnosticWithLocation[];
         getCompilerOptionsDiagnostics(): Diagnostic[];
         /**
          * @deprecated Use getEncodedSyntacticClassifications instead.