Merge pull request #23956 from Kingwl/emit-var-at-top

emit temporary vars at the top of the scope

src/compiler/core.ts

@@ -951,6 +951,21 @@ namespace ts {
         return to;
     }
 
+    /**
+     * Appends a range of value to begin of an array, returning the array.
+     *
+     * @param to The array to which `value` is to be appended. If `to` is `undefined`, a new array
+     * is created if `value` was appended.
+     * @param from The values to append to the array. If `from` is `undefined`, nothing is
+     * appended. If an element of `from` is `undefined`, that element is not appended.
+     */
+    export function prependRange<T>(to: T[], from: ReadonlyArray<T> | undefined): T[] | undefined {
+        if (from === undefined || from.length === 0) return to;
+        if (to === undefined) return from.slice();
+        to.unshift(...from);
+        return to;
+    }
+
     /**
      * @return Whether the value was added.
      */

src/compiler/transformers/es2015.ts

@@ -529,7 +529,7 @@ namespace ts {
                     createVariableStatement(/*modifiers*/ undefined,
                         createVariableDeclarationList(taggedTemplateStringDeclarations)));
             }
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
             exitSubtree(ancestorFacts, HierarchyFacts.None, HierarchyFacts.None);
             return updateSourceFileNode(
                 node,
@@ -836,7 +836,7 @@ namespace ts {
             setEmitFlags(statement, EmitFlags.NoComments | EmitFlags.NoTokenSourceMaps);
             statements.push(statement);
 
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
 
             const block = createBlock(setTextRange(createNodeArray(statements), /*location*/ node.members), /*multiLine*/ true);
             setEmitFlags(block, EmitFlags.NoComments);
@@ -979,7 +979,7 @@ namespace ts {
                 );
             }
 
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
 
             if (constructor) {
                 prependCaptureNewTargetIfNeeded(statements, constructor, /*copyOnWrite*/ false);
@@ -1894,7 +1894,7 @@ namespace ts {
             }
 
             const lexicalEnvironment = context.endLexicalEnvironment();
-            addRange(statements, lexicalEnvironment);
+            prependRange(statements, lexicalEnvironment);
 
             prependCaptureNewTargetIfNeeded(statements, node, /*copyOnWrite*/ false);
 
@@ -2712,7 +2712,7 @@ namespace ts {
                 if (loopOutParameters.length) {
                     copyOutParameters(loopOutParameters, CopyDirection.ToOutParameter, statements);
                 }
-                addRange(statements, lexicalEnvironment);
+                prependRange(statements, lexicalEnvironment);
                 loopBody = createBlock(statements, /*multiline*/ true);
             }
 
@@ -3309,10 +3309,12 @@ namespace ts {
             // expression, but we will restore them later to preserve comments and source maps.
             const body = cast(cast(skipOuterExpressions(node.expression), isArrowFunction).body, isBlock);
 
-            // The class statements are the statements generated by visiting the first statement of the
+            // The class statements are the statements generated by visiting the first statement with initializer of the
             // body (1), while all other statements are added to remainingStatements (2)
-            const classStatements = visitNodes(body.statements, visitor, isStatement, 0, 1);
-            const remainingStatements = visitNodes(body.statements, visitor, isStatement, 1, body.statements.length - 1);
+            const isVariableStatementWithInitializer = (stmt: Statement) => isVariableStatement(stmt) && !!firstOrUndefined(stmt.declarationList.declarations).initializer;
+            const bodyStatements = visitNodes(body.statements, visitor, isStatement);
+            const classStatements = filter(bodyStatements, isVariableStatementWithInitializer);
+            const remainingStatements = filter(bodyStatements, stmt => !isVariableStatementWithInitializer(stmt));
             const varStatement = cast(firstOrUndefined(classStatements), isVariableStatement);
 
             // We know there is only one variable declaration here as we verified this in an
@@ -3324,6 +3326,7 @@ namespace ts {
             // we see as an assignment, for example:
             //
             //  (function () {
+            //      var C_1;
             //      var C = C_1 = (function () {
             //          function C() {
             //          }
@@ -3332,7 +3335,6 @@ namespace ts {
             //      }());
             //      C = C_1 = __decorate([dec], C);
             //      return C;
-            //      var C_1;
             //  }())
             //
             const aliasAssignment = tryCast(initializer, isAssignmentExpression);

src/compiler/transformers/es2017.ts

@@ -412,7 +412,7 @@ namespace ts {
                     )
                 );
 
-                addRange(statements, endLexicalEnvironment());
+                prependRange(statements, endLexicalEnvironment());
 
                 const block = createBlock(statements, /*multiLine*/ true);
                 setTextRange(block, node.body);
@@ -443,7 +443,7 @@ namespace ts {
                 const declarations = endLexicalEnvironment();
                 if (some(declarations)) {
                     const block = convertToFunctionBody(expression);
-                    result = updateBlock(block, setTextRange(createNodeArray(concatenate(block.statements, declarations)), block.statements));
+                    result = updateBlock(block, setTextRange(createNodeArray(concatenate(declarations, block.statements)), block.statements));
                 }
                 else {
                     result = expression;

src/compiler/transformers/esnext.ts

@@ -663,7 +663,7 @@ namespace ts {
                 )
             );
 
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
             const block = updateBlock(node.body, statements);
 
             // Minor optimization, emit `_super` helper to capture `super` access in an arrow.
@@ -692,11 +692,11 @@ namespace ts {
                 statementOffset = addPrologue(statements, body.statements, /*ensureUseStrict*/ false, visitor);
             }
             addRange(statements, appendObjectRestAssignmentsIfNeeded(/*statements*/ undefined, node));
-            const trailingStatements = endLexicalEnvironment();
-            if (statementOffset > 0 || some(statements) || some(trailingStatements)) {
+            const leadingStatements = endLexicalEnvironment();
+            if (statementOffset > 0 || some(statements) || some(leadingStatements)) {
                 const block = convertToFunctionBody(body, /*multiLine*/ true);
+                prependRange(statements, leadingStatements);
                 addRange(statements, block.statements.slice(statementOffset));
-                addRange(statements, trailingStatements);
                 return updateBlock(block, setTextRange(createNodeArray(statements), block.statements));
             }
             return body;

src/compiler/transformers/generators.ts

@@ -586,7 +586,7 @@ namespace ts {
             transformAndEmitStatements(body.statements, statementOffset);
 
             const buildResult = build();
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
             statements.push(createReturn(buildResult));
 
             // Restore previous generator state

src/compiler/transformers/module/module.ts

@@ -97,7 +97,7 @@ namespace ts {
             append(statements, visitNode(currentModuleInfo.externalHelpersImportDeclaration, sourceElementVisitor, isStatement));
             addRange(statements, visitNodes(node.statements, sourceElementVisitor, isStatement, statementOffset));
             addExportEqualsIfNeeded(statements, /*emitAsReturn*/ false);
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
 
             const updated = updateSourceFileNode(node, setTextRange(createNodeArray(statements), node.statements));
             if (currentModuleInfo.hasExportStarsToExportValues && !compilerOptions.importHelpers) {
@@ -426,7 +426,7 @@ namespace ts {
 
             // End the lexical environment for the module body
             // and merge any new lexical declarations.
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
 
             const body = createBlock(statements, /*multiLine*/ true);
             if (currentModuleInfo.hasExportStarsToExportValues && !compilerOptions.importHelpers) {

src/compiler/transformers/module/system.ts

@@ -257,7 +257,7 @@ namespace ts {
             // We emit hoisted variables early to align roughly with our previous emit output.
             // Two key differences in this approach are:
             // - Temporary variables will appear at the top rather than at the bottom of the file
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
 
             const exportStarFunction = addExportStarIfNeeded(statements);
             const moduleObject = createObjectLiteral([

src/compiler/transformers/ts.ts

@@ -669,7 +669,7 @@ namespace ts {
                 setEmitFlags(statement, EmitFlags.NoComments | EmitFlags.NoTokenSourceMaps);
                 statements.push(statement);
 
-                addRange(statements, context.endLexicalEnvironment());
+                prependRange(statements, context.endLexicalEnvironment());
 
                 const iife = createImmediatelyInvokedArrowFunction(statements);
                 setEmitFlags(iife, EmitFlags.TypeScriptClassWrapper);
@@ -2685,8 +2685,9 @@ namespace ts {
 
             const statements: Statement[] = [];
             startLexicalEnvironment();
-            addRange(statements, map(node.members, transformEnumMember));
-            addRange(statements, endLexicalEnvironment());
+            const members = map(node.members, transformEnumMember);
+            prependRange(statements, endLexicalEnvironment());
+            addRange(statements, members);
 
             currentNamespaceContainerName = savedCurrentNamespaceLocalName;
             return createBlock(
@@ -3000,7 +3001,7 @@ namespace ts {
                 statementsLocation = moveRangePos(moduleBlock.statements, -1);
             }
 
-            addRange(statements, endLexicalEnvironment());
+            prependRange(statements, endLexicalEnvironment());
             currentNamespaceContainerName = savedCurrentNamespaceContainerName;
             currentNamespace = savedCurrentNamespace;
             currentScopeFirstDeclarationsOfName = savedCurrentScopeFirstDeclarationsOfName;

src/compiler/visitor.ts

@@ -145,7 +145,7 @@ namespace ts {
             statements = setTextRange(createNodeArray([createStatement(createLiteral("use strict")), ...statements]), statements);
         }
         const declarations = context.endLexicalEnvironment();
-        return setTextRange(createNodeArray(concatenate(statements, declarations)), statements);
+        return setTextRange(createNodeArray(concatenate(declarations, statements)), statements);
     }
 
     /**
@@ -1468,8 +1468,8 @@ namespace ts {
         }
 
         return isNodeArray(statements)
-            ? setTextRange(createNodeArray(concatenate(statements, declarations)), statements)
-            : addRange(statements, declarations);
+            ? setTextRange(createNodeArray(concatenate(declarations, statements)), statements)
+            : prependRange(statements, declarations);
     }
 
     /**