Specific diagnostic suggestions for unexpected keyword or identifier

src/compiler/diagnosticMessages.json

@@ -1360,6 +1360,50 @@
         "category": "Error",
         "code": 1432
     },
+    "Unexpected keyword or identifier.": {
+        "category": "Error",
+        "code": 1433
+    },
+    "Unknown keyword or identifier. Did you mean '{0}'?": {
+        "category": "Error",
+        "code": 1434
+    },
+    "Decorators must precede all other keywords for property declarations.": {
+        "category": "Error",
+        "code": 1435
+    },
+    "Namespace must be given a name.": {
+        "category": "Error",
+        "code": 1436
+    },
+    "Interface must be given a name.": {
+        "category": "Error",
+        "code": 1437
+    },
+    "Type alias must be given a name.": {
+        "category": "Error",
+        "code": 1438
+    },
+    "Variable declaration not allowed at this location.": {
+        "category": "Error",
+        "code": 1439
+    },
+    "Function call not allowed at this location.": {
+        "category": "Error",
+        "code": 1440
+    },
+    "Missing '=' before default property value.": {
+        "category": "Error",
+        "code": 1441
+    },
+    "Template literal not allowed as a string at this position.": {
+        "category": "Error",
+        "code": 1442
+    },
+    "Template literal not allowed as a string at this position. Did you mean '{0}'?": {
+        "category": "Error",
+        "code": 1443
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",
@@ -3264,6 +3308,10 @@
         "category": "Error",
         "code": 2802
     },
+    "Namespace name cannot be '{0}'.": {
+        "category": "Error",
+        "code": 2803
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

src/compiler/parser.ts

@@ -1518,6 +1518,138 @@ namespace ts {
             return false;
         }
 
+        const commonKeywords = [
+            "async",
+            "class",
+            "const",
+            "declare",
+            "export",
+            "function",
+            "interface",
+            "let",
+            "type",
+            "var",
+        ];
+
+        function parseSemicolonAfter(expression: Expression | PropertyName, initializer?: Node) {
+            // Consume the semicolon if it was explicitly provided.
+            if (canParseSemicolon()) {
+                if (token() === SyntaxKind.SemicolonToken) {
+                    nextToken();
+                }
+
+                return;
+            }
+
+            // The only way not having a semicolon after an expression when expected shouldn't create an error
+            // would be if we've there's an initializer, which would indicate the initializer already has an error
+            if (initializer) {
+                return;
+            }
+
+            // Tagged template literals are sometimes used in places where only simple strings are allowed, e.g.:
+            //   module `M1` {
+            //   ^^^^^^^^^^^ This block is parsed as a template literal as with module`M1`.
+            if (isTaggedTemplateExpression(expression)) {
+                parseErrorAt(skipTrivia(sourceText, expression.template.pos), expression.template.end, Diagnostics.Template_literal_not_allowed_as_a_string_at_this_position);
+                return;
+            }
+
+            // Otherwise, if this isn't a well-known keyword-like identifier, give the generic fallback message.
+            const expressionText = getExpressionText(expression);
+            if (!expressionText || !isIdentifierText(expressionText, languageVersion)) {
+                parseErrorAtCurrentToken(Diagnostics._0_expected, tokenToString(SyntaxKind.SemicolonToken));
+                return;
+            }
+
+            const pos = skipTrivia(sourceText, expression.pos);
+
+            // Some known keywords are likely signs of syntax being used improperly.
+            switch (expressionText) {
+                case "const":
+                case "let":
+                case "var":
+                    parseErrorAt(pos, expression.end, Diagnostics.Variable_declaration_not_allowed_at_this_location);
+                    return;
+
+                case "interface":
+                    parseErrorForExpectedName(scanner.getTokenText(), "{", Diagnostics.Interface_must_be_given_a_name, Diagnostics.Interface_name_cannot_be_0);
+                    return;
+
+                case "is":
+                    parseErrorAt(pos, scanner.getTextPos(), Diagnostics.A_type_predicate_is_only_allowed_in_return_type_position_for_functions_and_methods);
+                    return;
+
+                case "module":
+                case "namespace":
+                    parseErrorForExpectedName(scanner.getTokenText(), "{", Diagnostics.Namespace_must_be_given_a_name, Diagnostics.Namespace_name_cannot_be_0);
+                    return;
+
+                case "type":
+                    parseErrorForExpectedName(scanner.getTokenText(), "=", Diagnostics.Type_alias_must_be_given_a_name, Diagnostics.Type_alias_name_cannot_be_0);
+                    return;
+            }
+
+            // The user alternately might have misspelled or forgotten to add a space after a common keyword.
+            const suggestion = getSpellingSuggestion(expressionText, commonKeywords, n => n) || getSpaceSuggestion(expressionText);
+            if (suggestion) {
+                parseErrorAt(pos, expression.end, Diagnostics.Unknown_keyword_or_identifier_Did_you_mean_0, suggestion);
+            }
+
+            // We know this is a slightly more precise case than a missing expected semicolon.
+            parseErrorAt(pos, expression.end, Diagnostics.Unexpected_keyword_or_identifier);
+        }
+
+        function parseErrorForExpectedName(name: string, normalToken: string, blankDiagnostic: DiagnosticMessage, nameDiagnostic: DiagnosticMessage) {
+            if (name === normalToken) {
+                parseErrorAtCurrentToken(blankDiagnostic);
+            }
+            else {
+                parseErrorAtCurrentToken(nameDiagnostic, name);
+            }
+        }
+
+        function getSpaceSuggestion(expressionText: string) {
+            for (const keyword of commonKeywords) {
+                if (expressionText.length > keyword.length + 2 && startsWith(expressionText, keyword)) {
+                    return `${keyword} ${expressionText.slice(keyword.length)}`;
+                }
+            }
+
+            return undefined;
+        }
+
+        function parseSemicolonAfterPropertyName(name: PropertyName, type: TypeNode | undefined, initializer: Expression | undefined) {
+            switch (scanner.getTokenText()) {
+                case "@":
+                    parseErrorAtCurrentToken(Diagnostics.Decorators_must_precede_all_other_keywords_for_property_declarations);
+                    return;
+
+                case "(":
+                    parseErrorAtCurrentToken(Diagnostics.Function_call_not_allowed_at_this_location);
+                    nextToken();
+                    return;
+            }
+
+            if (type && !canParseSemicolon()) {
+                if (initializer) {
+                    parseErrorAtCurrentToken(Diagnostics._0_expected, tokenToString(SyntaxKind.SemicolonToken));
+                }
+                else {
+                    parseErrorAtCurrentToken(Diagnostics.Missing_before_default_property_value);
+                }
+                return;
+            }
+
+            return parseSemicolonAfter(name, initializer);
+        }
+
+        function getExpressionText(expression: Expression | PropertyName) {
+            return expression && ts.isIdentifier(expression)
+                ? expression.escapedText.toString()
+                : undefined;
+        }
+
         function parseExpectedJSDoc(kind: JSDocSyntaxKind) {
             if (token() === kind) {
                 nextTokenJSDoc();
@@ -5786,7 +5918,7 @@ namespace ts {
                 identifierCount++;
                 expression = finishNode(factory.createIdentifier(""), getNodePos());
             }
-            parseSemicolon();
+            parseSemicolonAfter(expression);
             return finishNode(factory.createThrowStatement(expression), pos);
         }
 
@@ -5847,7 +5979,7 @@ namespace ts {
                 node = factory.createLabeledStatement(expression, parseStatement());
             }
             else {
-                parseSemicolon();
+                parseSemicolonAfter(expression);
                 node = factory.createExpressionStatement(expression);
                 if (hasParen) {
                     // do not parse the same jsdoc twice
@@ -6440,7 +6572,7 @@ namespace ts {
             const exclamationToken = !questionToken && !scanner.hasPrecedingLineBreak() ? parseOptionalToken(SyntaxKind.ExclamationToken) : undefined;
             const type = parseTypeAnnotation();
             const initializer = doOutsideOfContext(NodeFlags.YieldContext | NodeFlags.AwaitContext | NodeFlags.DisallowInContext, parseInitializer);
-            parseSemicolon();
+            parseSemicolonAfterPropertyName(name, type, initializer);
             const node = factory.createPropertyDeclaration(decorators, modifiers, name, questionToken || exclamationToken, type, initializer);
             return withJSDoc(finishNode(node, pos), hasJSDoc);
         }

tests/baselines/reference/ClassDeclaration26.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/compiler/ClassDeclaration26.ts(2,22): error TS1005: ';' expected.
+tests/cases/compiler/ClassDeclaration26.ts(2,18): error TS1439: Variable declaration not allowed at this location.
 tests/cases/compiler/ClassDeclaration26.ts(4,5): error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
 tests/cases/compiler/ClassDeclaration26.ts(4,20): error TS1005: ',' expected.
 tests/cases/compiler/ClassDeclaration26.ts(4,23): error TS1005: '=>' expected.
@@ -8,8 +8,8 @@ tests/cases/compiler/ClassDeclaration26.ts(5,1): error TS1128: Declaration or st
 ==== tests/cases/compiler/ClassDeclaration26.ts (5 errors) ====
     class C {
         public const var export foo = 10;
-                         ~~~~~~
-!!! error TS1005: ';' expected.
+                     ~~~
+!!! error TS1439: Variable declaration not allowed at this location.
 
         var constructor() { }
         ~~~

tests/baselines/reference/anonymousModules.errors.txt

@@ -1,24 +1,24 @@
 tests/cases/compiler/anonymousModules.ts(1,1): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
-tests/cases/compiler/anonymousModules.ts(1,8): error TS1005: ';' expected.
+tests/cases/compiler/anonymousModules.ts(1,8): error TS1436: Namespace must be given a name.
 tests/cases/compiler/anonymousModules.ts(4,2): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
-tests/cases/compiler/anonymousModules.ts(4,9): error TS1005: ';' expected.
+tests/cases/compiler/anonymousModules.ts(4,9): error TS1436: Namespace must be given a name.
 tests/cases/compiler/anonymousModules.ts(10,2): error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
-tests/cases/compiler/anonymousModules.ts(10,9): error TS1005: ';' expected.
+tests/cases/compiler/anonymousModules.ts(10,9): error TS1436: Namespace must be given a name.
 
 
 ==== tests/cases/compiler/anonymousModules.ts (6 errors) ====
     module {
     ~~~~~~
 !!! error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
            ~
-!!! error TS1005: ';' expected.
+!!! error TS1436: Namespace must be given a name.
     	export var foo = 1;
 
     	module {
     	~~~~~~
 !!! error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
     	       ~
-!!! error TS1005: ';' expected.
+!!! error TS1436: Namespace must be given a name.
     		export var bar = 1;
     	}
 
@@ -28,7 +28,7 @@ tests/cases/compiler/anonymousModules.ts(10,9): error TS1005: ';' expected.
     	~~~~~~
 !!! error TS2580: Cannot find name 'module'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
     	       ~
-!!! error TS1005: ';' expected.
+!!! error TS1436: Namespace must be given a name.
     		var x = bar;
     	}
     }

tests/baselines/reference/classUpdateTests.errors.txt

@@ -11,14 +11,16 @@ tests/cases/compiler/classUpdateTests.ts(95,1): error TS1128: Declaration or sta
 tests/cases/compiler/classUpdateTests.ts(99,3): error TS1128: Declaration or statement expected.
 tests/cases/compiler/classUpdateTests.ts(101,1): error TS1128: Declaration or statement expected.
 tests/cases/compiler/classUpdateTests.ts(105,3): error TS1128: Declaration or statement expected.
-tests/cases/compiler/classUpdateTests.ts(105,14): error TS1005: ';' expected.
+tests/cases/compiler/classUpdateTests.ts(105,10): error TS1433: Unexpected keyword or identifier.
+tests/cases/compiler/classUpdateTests.ts(105,14): error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
 tests/cases/compiler/classUpdateTests.ts(107,1): error TS1128: Declaration or statement expected.
 tests/cases/compiler/classUpdateTests.ts(111,3): error TS1128: Declaration or statement expected.
-tests/cases/compiler/classUpdateTests.ts(111,15): error TS1005: ';' expected.
+tests/cases/compiler/classUpdateTests.ts(111,11): error TS1433: Unexpected keyword or identifier.
+tests/cases/compiler/classUpdateTests.ts(111,15): error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
 tests/cases/compiler/classUpdateTests.ts(113,1): error TS1128: Declaration or statement expected.
 
 
-==== tests/cases/compiler/classUpdateTests.ts (16 errors) ====
+==== tests/cases/compiler/classUpdateTests.ts (18 errors) ====
     //
     // test codegen for instance properties
     //
@@ -154,8 +156,10 @@ tests/cases/compiler/classUpdateTests.ts(113,1): error TS1128: Declaration or st
     		public this.p1 = 0; // ERROR
     		~~~~~~
 !!! error TS1128: Declaration or statement expected.
+    		       ~~~~
+!!! error TS1433: Unexpected keyword or identifier.
     		           ~
-!!! error TS1005: ';' expected.
+!!! error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
     	}
     }
     ~
@@ -166,8 +170,10 @@ tests/cases/compiler/classUpdateTests.ts(113,1): error TS1128: Declaration or st
     		private this.p1 = 0; // ERROR
     		~~~~~~~
 !!! error TS1128: Declaration or statement expected.
+    		        ~~~~
+!!! error TS1433: Unexpected keyword or identifier.
     		            ~
-!!! error TS1005: ';' expected.
+!!! error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
     	}
     }
     ~