feat(server): Definitions for sources compiled with declarationMap go to original source

The TypeScript language service has the ability to map definitions back
to their original source when the library code was compiled with
`declarationMap`. However, this functionality is not exposed as public
API. As a result, these methods could change in the future without our knowledge.

resolves #1588

Author: atscott

server/src/session.ts

@@ -20,7 +20,7 @@ import {readNgCompletionData, tsCompletionEntryToLspCompletionItem} from './comp
 import {tsDiagnosticToLspDiagnostic} from './diagnostic';
 import {resolveAndRunNgcc} from './ngcc';
 import {ServerHost} from './server_host';
-import {filePathToUri, isConfiguredProject, isDebugMode, lspPositionToTsPosition, lspRangeToTsPositions, MruTracker, tsDisplayPartsToText, tsTextSpanToLspRange, uriToFilePath} from './utils';
+import {filePathToUri, getMappedDefinitionInfo, isConfiguredProject, isDebugMode, lspPositionToTsPosition, lspRangeToTsPositions, MruTracker, tsDisplayPartsToText, tsTextSpanToLspRange, uriToFilePath} from './utils';
 
 export interface SessionOptions {
   host: ServerHost;
@@ -924,9 +924,16 @@ export class Session {
       if (!scriptInfo && d.textSpan.length > 0) {
         continue;
       }
-      const range = scriptInfo ? tsTextSpanToLspRange(scriptInfo, d.textSpan) : EMPTY_RANGE;
 
-      const targetUri = filePathToUri(d.fileName);
+      let mappedInfo = d;
+      let range = EMPTY_RANGE;
+      if (scriptInfo) {
+        const project = this.getDefaultProjectForScriptInfo(scriptInfo);
+        mappedInfo = project ? getMappedDefinitionInfo(d, project) : mappedInfo;
+        range = tsTextSpanToLspRange(scriptInfo, mappedInfo.textSpan);
+      }
+
+      const targetUri = filePathToUri(mappedInfo.fileName);
       results.push({
         originSelectionRange,
         targetUri,

server/src/utils.ts

@@ -143,3 +143,69 @@ export class MruTracker {
 export function tsDisplayPartsToText(parts: ts.SymbolDisplayPart[]): string {
   return parts.map(dp => dp.text).join('');
 }
+
+interface DocumentPosition {
+  fileName: string;
+  pos: number;
+}
+
+/**
+ *
+ * This function attempts to use *internal* TypeScript APIs to find the original source spans for
+ * the `ts.DefinitionInfo` using source maps. If it fails, this function returns the same
+ * `ts.DefinitionInfo` that was passed in.
+ *
+ * @see https://github.com/angular/vscode-ng-language-service/issues/1588
+ */
+export function getMappedDefinitionInfo(
+    info: ts.DefinitionInfo, project: ts.server.Project): ts.DefinitionInfo {
+  try {
+    const mappedDocumentSpan = getMappedDocumentSpan(info, project);
+    return {...info, ...mappedDocumentSpan};
+  } catch {
+    return info;
+  }
+}
+
+function getMappedDocumentSpan(
+    documentSpan: ts.DocumentSpan, project: ts.server.Project): ts.DocumentSpan|undefined {
+  const newPosition = getMappedLocation(documentSpanLocation(documentSpan), project);
+  if (!newPosition) return undefined;
+  return {
+    fileName: newPosition.fileName,
+    textSpan: {start: newPosition.pos, length: documentSpan.textSpan.length},
+    originalFileName: documentSpan.fileName,
+    originalTextSpan: documentSpan.textSpan,
+    contextSpan: getMappedContextSpan(documentSpan, project),
+    originalContextSpan: documentSpan.contextSpan
+  };
+}
+
+function getMappedLocation(
+    location: DocumentPosition, project: ts.server.Project): DocumentPosition|undefined {
+  const mapsTo = (project as any).getSourceMapper().tryGetSourcePosition(location);
+  return mapsTo &&
+          (project.projectService as any).fileExists(ts.server.toNormalizedPath(mapsTo.fileName)) ?
+      mapsTo :
+      undefined;
+}
+
+function documentSpanLocation({fileName, textSpan}: ts.DocumentSpan): DocumentPosition {
+  return {fileName, pos: textSpan.start};
+}
+
+function getMappedContextSpan(
+    documentSpan: ts.DocumentSpan, project: ts.server.Project): ts.TextSpan|undefined {
+  const contextSpanStart = documentSpan.contextSpan &&
+      getMappedLocation({fileName: documentSpan.fileName, pos: documentSpan.contextSpan.start},
+                        project);
+  const contextSpanEnd = documentSpan.contextSpan &&
+      getMappedLocation({
+                          fileName: documentSpan.fileName,
+                          pos: documentSpan.contextSpan.start + documentSpan.contextSpan.length
+                         },
+                        project);
+  return contextSpanStart && contextSpanEnd ?
+      {start: contextSpanStart.pos, length: contextSpanEnd.pos - contextSpanStart.pos} :
+      undefined;
+}