For duplicate source files of the same package, make one redirect to the other

src/compiler/program.ts

@@ -479,7 +479,7 @@ namespace ts {
         // Maps from a SourceFile's `.path` to the name of the package it was imported with.
         let sourceFileToPackageName = createMap<string>();
         // See `sourceFileIsRedirectedTo`.
-        let isSourceFileTargetOfRedirect = createMap<true>();
+        let redirectTargetsSet = createMap<true>();
 
         const filesByName = createMap<SourceFile | undefined>();
         // stores 'filename -> file association' ignoring case
@@ -558,7 +558,7 @@ namespace ts {
             dropDiagnosticsProducingTypeChecker,
             getSourceFileFromReference,
             sourceFileToPackageName,
-            isSourceFileTargetOfRedirect,
+            redirectTargetsSet,
         };
 
         verifyCompilerOptions();
@@ -797,12 +797,12 @@ namespace ts {
                 if (oldSourceFile.redirect) {
                     // We got `newSourceFile` by path, so it is actually for the underlying file.
                     // This lets us know if the underlying file has changed. If it has we should break the redirect.
-                    if (newSourceFile !== oldSourceFile.redirect.underlying) {
+                    if (newSourceFile !== oldSourceFile.redirect.unredirected) {
                         // Underlying file has changed. Might not redirect anymore. Must rebuild program.
                         return oldProgram.structureIsReused = StructureIsReused.Not;
                     }
                 }
-                else if (oldProgram.isSourceFileTargetOfRedirect.has(oldSourceFile.path)) {
+                else if (oldProgram.redirectTargetsSet.has(oldSourceFile.path)) {
                     // This is similar to the above case. If a redirected-to source file changes, the redirect may be broken.
                     if (newSourceFile !== oldSourceFile) {
                         return oldProgram.structureIsReused = StructureIsReused.Not;
@@ -941,7 +941,7 @@ namespace ts {
             resolvedTypeReferenceDirectives = oldProgram.getResolvedTypeReferenceDirectives();
 
             sourceFileToPackageName = oldProgram.sourceFileToPackageName;
-            isSourceFileTargetOfRedirect = oldProgram.isSourceFileTargetOfRedirect;
+            redirectTargetsSet = oldProgram.redirectTargetsSet;
 
             return oldProgram.structureIsReused = StructureIsReused.Completely;
         }
@@ -1597,19 +1597,19 @@ namespace ts {
             }
         }
 
-        function createRedirectSourceFile(redirectTo: SourceFile, underlying: SourceFile, fileName: string, path: Path): SourceFile {
-            const redirect: SourceFile = Object.create(redirectTo);
+        function createRedirectSourceFile(redirectTarget: SourceFile, unredirected: SourceFile, fileName: string, path: Path): SourceFile {
+            const redirect: SourceFile = Object.create(redirectTarget);
             redirect.fileName = fileName;
             redirect.path = path;
-            redirect.redirect = { redirectTo, underlying };
+            redirect.redirect = { redirectTarget, unredirected };
             Object.defineProperties(redirect, {
                 id: {
-                    get(this: SourceFile) { return this.redirect.redirectTo.id; },
-                    set(this: SourceFile, value: SourceFile["id"]) { this.redirect.redirectTo.id = value; },
+                    get(this: SourceFile) { return this.redirect.redirectTarget.id; },
+                    set(this: SourceFile, value: SourceFile["id"]) { this.redirect.redirectTarget.id = value; },
                 },
                 symbol: {
-                    get(this: SourceFile) { return this.redirect.redirectTo.symbol; },
-                    set(this: SourceFile, value: SourceFile["symbol"]) { this.redirect.redirectTo.symbol = value; },
+                    get(this: SourceFile) { return this.redirect.redirectTarget.symbol; },
+                    set(this: SourceFile, value: SourceFile["symbol"]) { this.redirect.redirectTarget.symbol = value; },
                 },
             });
             return redirect;
@@ -1666,7 +1666,7 @@ namespace ts {
                     // Some other SourceFile already exists with this package name and version.
                     // Instead of creating a duplicate, just redirect to the existing one.
                     const dupFile = createRedirectSourceFile(fileFromPackageId, file, fileName, path);
-                    isSourceFileTargetOfRedirect.set(fileFromPackageId.path, true);
+                    redirectTargetsSet.set(fileFromPackageId.path, true);
                     filesByName.set(path, dupFile);
                     sourceFileToPackageName.set(path, packageId.name);
                     files.push(dupFile);

src/compiler/types.ts

@@ -2330,12 +2330,12 @@ namespace ts {
          */
         /* @internal */ redirect?: {
             /** Source file this redirects to. */
-            readonly redirectTo: SourceFile,
+            readonly redirectTarget: SourceFile,
             /**
              * Source file for the duplicate package. This will not be used by the Program,
              * but we need to keep this around so we can watch for changes in underlying.
              */
-            readonly underlying: SourceFile,
+            readonly unredirected: SourceFile,
         } | undefined;
 
         amdDependencies: AmdDependency[];
@@ -2511,8 +2511,8 @@ namespace ts {
 
         /** Given a source file, get the name of the package it was imported from. */
         /* @internal */ sourceFileToPackageName: Map<string>;
-        /** True if some other source file redirects to this one. */
-        /* @internal */ isSourceFileTargetOfRedirect: Map<true>;
+        /** Set of all source files that some other source file redirects to. */
+        /* @internal */ redirectTargetsSet: Map<true>;
     }
 
     /* @internal */

src/harness/unittests/reuseProgramStructure.ts

@@ -110,7 +110,7 @@ namespace ts {
         const files = arrayToMap(texts, t => t.name, t => {
             if (oldProgram) {
                 let oldFile = <SourceFileWithText>oldProgram.getSourceFile(t.name);
-                if (oldFile && oldFile.redirect) oldFile = oldFile.redirect.underlying;
+                if (oldFile && oldFile.redirect) oldFile = oldFile.redirect.unredirected;
                 if (oldFile && oldFile.sourceText.getVersion() === t.text.getVersion()) {
                     return oldFile;
                 }