From 015a472a6e12639ab1f50074d2ccc5db14565ef2 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wewigham@microsoft.com>
Date: Tue, 11 Feb 2020 14:11:59 -0800
Subject: [PATCH 1/3] Fix getTypeAtLocation for `as const` to not issue a
 diagnostic

---
 src/compiler/checker.ts                |  5 +++++
 src/testRunner/unittests/programApi.ts | 15 +++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f7d72d3950e49..ecd185452ce0b 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11336,6 +11336,11 @@ namespace ts {
         function getTypeFromTypeReference(node: TypeReferenceType): Type {
             const links = getNodeLinks(node);
             if (!links.resolvedType) {
+                // handle LS queries on the `const` in `x as const` by resolving to the type of `x`
+                if (isTypeReferenceNode(node) && isIdentifier(node.typeName) && idText(node.typeName) === "const" && isAssertionExpression(node.parent)) {
+                    links.resolvedSymbol = unknownSymbol;
+                    return links.resolvedType = checkExpressionCached(node.parent.expression);
+                }
                 let symbol: Symbol | undefined;
                 let type: Type | undefined;
                 const meaning = SymbolFlags.Type;
diff --git a/src/testRunner/unittests/programApi.ts b/src/testRunner/unittests/programApi.ts
index 5f5251afaf253..9c65a54ab758d 100644
--- a/src/testRunner/unittests/programApi.ts
+++ b/src/testRunner/unittests/programApi.ts
@@ -178,4 +178,19 @@ namespace ts {
             assert.isNotNaN(program.getIdentifierCount());
         });
     });
+
+
+    describe("unittests:: programApi:: Program.getDiagnosticsProducingTypeChecker / Program.getSemanticDiagnostics", () => {
+        it("does not produce errors on `as const` it would not normally produce on the command line", () => {
+            const main = new documents.TextDocument("/main.ts", '0 as const');
+
+            const fs = vfs.createFromFileSystem(Harness.IO, /*ignoreCase*/ false, { documents: [main], cwd: "/" });
+            const program = createProgram(["/main.ts"], {}, new fakes.CompilerHost(fs, { newLine: NewLineKind.LineFeed }));
+            const typeChecker = program.getDiagnosticsProducingTypeChecker();
+            const sourceFile = program.getSourceFile("main.ts")!;
+            typeChecker.getTypeAtLocation(((sourceFile.statements[0] as ExpressionStatement).expression as AsExpression).type);
+            const diag = program.getSemanticDiagnostics();
+            assert.isEmpty(diag);
+        });
+    });
 }

From 6feb34997c3a26ac4576b813beefd719758c847d Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wewigham@microsoft.com>
Date: Tue, 11 Feb 2020 14:18:04 -0800
Subject: [PATCH 2/3] use existing helpers for checks

---
 src/compiler/checker.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ecd185452ce0b..e1a25d6b87140 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -11337,7 +11337,7 @@ namespace ts {
             const links = getNodeLinks(node);
             if (!links.resolvedType) {
                 // handle LS queries on the `const` in `x as const` by resolving to the type of `x`
-                if (isTypeReferenceNode(node) && isIdentifier(node.typeName) && idText(node.typeName) === "const" && isAssertionExpression(node.parent)) {
+                if (isConstTypeReference(node) && isAssertionExpression(node.parent)) {
                     links.resolvedSymbol = unknownSymbol;
                     return links.resolvedType = checkExpressionCached(node.parent.expression);
                 }

From 8bcd4f4c5ca528fd6ecef9419c92b00ef47d2bec Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wewigham@microsoft.com>
Date: Tue, 11 Feb 2020 14:32:21 -0800
Subject: [PATCH 3/3] Fix lint

---
 src/testRunner/unittests/programApi.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/testRunner/unittests/programApi.ts b/src/testRunner/unittests/programApi.ts
index 9c65a54ab758d..51405aece41a3 100644
--- a/src/testRunner/unittests/programApi.ts
+++ b/src/testRunner/unittests/programApi.ts
@@ -182,7 +182,7 @@ namespace ts {
 
     describe("unittests:: programApi:: Program.getDiagnosticsProducingTypeChecker / Program.getSemanticDiagnostics", () => {
         it("does not produce errors on `as const` it would not normally produce on the command line", () => {
-            const main = new documents.TextDocument("/main.ts", '0 as const');
+            const main = new documents.TextDocument("/main.ts", "0 as const");
 
             const fs = vfs.createFromFileSystem(Harness.IO, /*ignoreCase*/ false, { documents: [main], cwd: "/" });
             const program = createProgram(["/main.ts"], {}, new fakes.CompilerHost(fs, { newLine: NewLineKind.LineFeed }));