From 2e4f1297109f60d7a416116098ec5eb448c5253b Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Tue, 2 Aug 2022 15:50:31 -0700
Subject: [PATCH 1/2] Fix up code so we don't crash when TS itself is emitted
 with let/const

---
 src/compiler/checker.ts  | 6 +++---
 src/services/services.ts | 6 +++++-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 7ac4bb7d5a52b..aa0d50dcfbf9d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -27022,10 +27022,10 @@ namespace ts {
                 case AssignmentDeclarationKind.ExportsProperty:
                 case AssignmentDeclarationKind.Prototype:
                 case AssignmentDeclarationKind.PrototypeProperty:
-                    let valueDeclaration = binaryExpression.left.symbol?.valueDeclaration;
-                    // falls through
                 case AssignmentDeclarationKind.ModuleExports:
-                    valueDeclaration ||= binaryExpression.symbol?.valueDeclaration;
+                    const valueDeclaration = kind !== AssignmentDeclarationKind.ModuleExports
+                        ? binaryExpression.left.symbol?.valueDeclaration
+                        : binaryExpression.symbol?.valueDeclaration;
                     const annotated = valueDeclaration && getEffectiveTypeAnnotationNode(valueDeclaration);
                     return annotated ? getTypeFromTypeNode(annotated) : undefined;
                 case AssignmentDeclarationKind.ObjectDefinePropertyValue:
diff --git a/src/services/services.ts b/src/services/services.ts
index ecd7eae9530c9..15540e28acf99 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1363,6 +1363,11 @@ namespace ts {
                 onUnRecoverableConfigFileDiagnostic: noop,
             };
 
+            // The call to isProgramUptoDate below may refer back to documentRegistryBucketKey;
+            // calculate this early so it's not undefined if downleveled to a var (or, if emitted
+            // as a const variable without downleveling, doesn't crash).
+            const documentRegistryBucketKey = documentRegistry.getKeyForCompilationSettings(newSettings);
+
             // If the program is already up-to-date, we can reuse it
             if (isProgramUptoDate(program, rootFileNames, newSettings, (_path, fileName) => host.getScriptVersion(fileName), fileName => compilerHost!.fileExists(fileName), hasInvalidatedResolution, hasChangedAutomaticTypeDirectiveNames, getParsedCommandLine, projectReferences)) {
                 return;
@@ -1374,7 +1379,6 @@ namespace ts {
             // the program points to old source files that have been invalidated because of
             // incremental parsing.
 
-            const documentRegistryBucketKey = documentRegistry.getKeyForCompilationSettings(newSettings);
             const options: CreateProgramOptions = {
                 rootNames: rootFileNames,
                 options: newSettings,

From e53273d131b3c2cec0dab1495fcd80aa1c3315ce Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Thu, 4 Aug 2022 09:28:55 -0700
Subject: [PATCH 2/2] Make switch case code equivalent

---
 src/compiler/checker.ts | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index aa0d50dcfbf9d..a364e7d63ad5e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -27023,9 +27023,11 @@ namespace ts {
                 case AssignmentDeclarationKind.Prototype:
                 case AssignmentDeclarationKind.PrototypeProperty:
                 case AssignmentDeclarationKind.ModuleExports:
-                    const valueDeclaration = kind !== AssignmentDeclarationKind.ModuleExports
-                        ? binaryExpression.left.symbol?.valueDeclaration
-                        : binaryExpression.symbol?.valueDeclaration;
+                    let valueDeclaration: Declaration | undefined;
+                    if (kind !== AssignmentDeclarationKind.ModuleExports) {
+                        valueDeclaration = binaryExpression.left.symbol?.valueDeclaration;
+                    }
+                    valueDeclaration ||= binaryExpression.symbol?.valueDeclaration;
                     const annotated = valueDeclaration && getEffectiveTypeAnnotationNode(valueDeclaration);
                     return annotated ? getTypeFromTypeNode(annotated) : undefined;
                 case AssignmentDeclarationKind.ObjectDefinePropertyValue: