Emit source positions for open/close braces (#47924)

src/compiler/emitter.ts

@@ -927,6 +927,7 @@ export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFi
             inlineSourceMap: compilerOptions.inlineSourceMap,
             extendedDiagnostics: compilerOptions.extendedDiagnostics,
             onlyPrintJsDocStyle: true,
+            omitBraceSourceMapPositions: true,
             writeBundleFileInfo: !!bundleBuildInfo,
             recordInternalSection: !!bundleBuildInfo,
             relativeToBuildInfo,
@@ -1391,6 +1392,7 @@ export function createPrinter(printerOptions: PrinterOptions = {}, handlers: Pri
     } = handlers;
 
     var extendedDiagnostics = !!printerOptions.extendedDiagnostics;
+    var omitBraceSourcePositions = !!printerOptions.omitBraceSourceMapPositions;
     var newLine = getNewLineCharacter(printerOptions);
     var moduleKind = getEmitModuleKind(printerOptions);
     var bundledHelpers = new Map<string, boolean>();
@@ -3578,7 +3580,18 @@ export function createPrinter(printerOptions: PrinterOptions = {}, handlers: Pri
                 decreaseIndent();
             }
         }
-        pos = writeTokenText(token, writer, pos);
+
+        // We don't emit source positions for most tokens as it tends to be quite noisy, however
+        // we need to emit source positions for open and close braces so that tools like istanbul
+        // can map branches for code coverage. However, we still omit brace source positions when
+        // the output is a declaration file.
+        if (!omitBraceSourcePositions && (token === SyntaxKind.OpenBraceToken || token === SyntaxKind.CloseBraceToken)) {
+            pos = writeToken(token, pos, writer, contextNode);
+        }
+        else {
+            pos = writeTokenText(token, writer, pos);
+        }
+
         if (isSimilarNode && contextNode.end !== pos) {
             const isJsxExprContext = contextNode.kind === SyntaxKind.JsxExpression;
             emitTrailingCommentsOfPosition(pos, /*prefixSpace*/ !isJsxExprContext, /*forceNoNewline*/ isJsxExprContext);

src/compiler/types.ts

@@ -9476,6 +9476,7 @@ export interface PrinterOptions {
     /** @internal */ sourceMap?: boolean;
     /** @internal */ inlineSourceMap?: boolean;
     /** @internal */ inlineSources?: boolean;
+    /** @internal*/ omitBraceSourceMapPositions?: boolean;
     /** @internal */ extendedDiagnostics?: boolean;
     /** @internal */ onlyPrintJsDocStyle?: boolean;
     /** @internal */ neverAsciiEscape?: boolean;