Adds a preview link to the baseline emits for sourcemaps (microsoft#37111)

Author: Orta

src/harness/harnessIO.ts

@@ -847,12 +847,28 @@ namespace Harness {
                     result.maps.forEach(sourceMap => {
                         if (sourceMapCode) sourceMapCode += "\r\n";
                         sourceMapCode += fileOutput(sourceMap, harnessSettings);
+                        if (!options.inlineSourceMap) {
+                            sourceMapCode += createSourceMapPreviewLink(sourceMap.text, result);
+                        }
                     });
                 }
                 Baseline.runBaseline(baselinePath.replace(/\.tsx?/, ".js.map"), sourceMapCode);
             }
         }
 
+        function createSourceMapPreviewLink(sourcemap: string, result: compiler.CompilationResult) {
+            const sourcemapJSON = JSON.parse(sourcemap);
+            const outputJSFile = result.outputs.find(td => td.file.endsWith(sourcemapJSON.file));
+            if (!outputJSFile) return "";
+
+            const sourceTDs = ts.map(sourcemapJSON.sources, (s: string) => result.inputs.find(td => td.file.endsWith(s)));
+            const anyUnfoundSources = ts.contains(sourceTDs, /*value*/ undefined);
+            if (anyUnfoundSources) return "";
+
+            const hash = "#base64," + ts.map([outputJSFile.text, sourcemap].concat(sourceTDs.map(td => td!.text)), (s) => ts.convertToBase64(decodeURIComponent(encodeURIComponent(s)))).join(",");
+            return "\n//// https://sokra.github.io/source-map-visualization" + hash + "\n";
+        }
+
         export function doJsEmitBaseline(baselinePath: string, header: string, options: ts.CompilerOptions, result: compiler.CompilationResult, tsConfigFiles: readonly TestFile[], toBeCompiled: readonly TestFile[], otherFiles: readonly TestFile[], harnessSettings: TestCaseParser.CompilerSettings) {
             if (!options.noEmit && !options.emitDeclarationOnly && result.js.size === 0 && result.diagnostics.length === 0) {
                 throw new Error("Expected at least one js file to be emitted or at least one error to be created.");