If import is used in the file, prefer that import specifier over calculating new one

Fixes #38111

Author: sheetalkamat

src/compiler/checker.ts

@@ -4378,7 +4378,8 @@ namespace ts {
                         getProjectReferenceRedirect: fileName => host.getProjectReferenceRedirect(fileName),
                         isSourceOfProjectReferenceRedirect: fileName => host.isSourceOfProjectReferenceRedirect(fileName),
                         fileExists: fileName => host.fileExists(fileName),
-                        getCompilerOptions: () => host.getCompilerOptions()
+                        getCompilerOptions: () => host.getCompilerOptions(),
+                        getFileIncludeReasons: () => host.getFileIncludeReasons(),
                     } : undefined },
                     encounteredError: false,
                     visitedTypes: undefined,

src/compiler/emitter.ts

@@ -849,7 +849,8 @@ namespace ts {
             useCaseSensitiveFileNames: () => host.useCaseSensitiveFileNames(),
             getProgramBuildInfo: returnUndefined,
             getSourceFileFromReference: returnUndefined,
-            redirectTargetsMap: createMultiMap()
+            redirectTargetsMap: createMultiMap(),
+            getFileIncludeReasons: notImplemented,
         };
         emitFiles(
             notImplementedResolver,

src/compiler/moduleSpecifiers.ts

@@ -105,6 +105,14 @@ namespace ts.moduleSpecifiers {
         const moduleSourceFile = getSourceFileOfNode(moduleSymbol.valueDeclaration || getNonAugmentationDeclaration(moduleSymbol));
         const modulePaths = getAllModulePaths(importingSourceFile.path, moduleSourceFile.originalFileName, host);
 
+        const existingSpecifier = forEach(modulePaths, modulePath => forEach(
+            host.getFileIncludeReasons().get(toPath(modulePath.path, host.getCurrentDirectory(), info.getCanonicalFileName)),
+            reason => reason.kind === FileIncludeKind.Import && reason.file === importingSourceFile.path ?
+                getModuleNameStringLiteralAt(importingSourceFile, reason.index).text :
+                undefined
+        ));
+        if (existingSpecifier) return [existingSpecifier];
+
         const preferences = getPreferences(userPreferences, compilerOptions, importingSourceFile);
         const importedFileIsInNodeModules = some(modulePaths, p => p.isInNodeModules);
 

src/compiler/program.ts

@@ -1649,6 +1649,7 @@ namespace ts {
                 getProgramBuildInfo: () => program.getProgramBuildInfo && program.getProgramBuildInfo(),
                 getSourceFileFromReference: (file, ref) => program.getSourceFileFromReference(file, ref),
                 redirectTargetsMap,
+                getFileIncludeReasons: program.getFileIncludeReasons,
             };
         }
 
@@ -3973,7 +3974,8 @@ namespace ts {
         return res;
     }
 
-    function getModuleNameStringLiteralAt({ imports, moduleAugmentations }: SourceFile, index: number): StringLiteralLike {
+    /* @internal */
+    export function getModuleNameStringLiteralAt({ imports, moduleAugmentations }: SourceFile, index: number): StringLiteralLike {
         if (index < imports.length) return imports[index];
         let augIndex = imports.length;
         for (const aug of moduleAugmentations) {

src/compiler/types.ts

@@ -7947,6 +7947,7 @@ namespace ts {
         getProjectReferenceRedirect(fileName: string): string | undefined;
         isSourceOfProjectReferenceRedirect(fileName: string): boolean;
         getCompilerOptions(): CompilerOptions;
+        getFileIncludeReasons(): MultiMap<Path, FileIncludeReason>;
     }
 
     // Note: this used to be deprecated in our public API, but is still used internally

src/services/utilities.ts

@@ -1836,6 +1836,7 @@ namespace ts {
             isSourceOfProjectReferenceRedirect: fileName => program.isSourceOfProjectReferenceRedirect(fileName),
             getCompilerOptions: () => program.getCompilerOptions(),
             getNearestAncestorDirectoryWithPackageJson: maybeBind(host, host.getNearestAncestorDirectoryWithPackageJson),
+            getFileIncludeReasons: () => program.getFileIncludeReasons(),
         };
     }
 

tests/baselines/reference/tsbuild/declarationEmit/initial-build/when-declaration-file-used-inferred-type-from-referenced-project.js

@@ -109,7 +109,7 @@ exports.__esModule = true;
 }
 
 //// [/src/packages/pkg2/lib/src/index.d.ts]
-export declare function fn4(): import("../../pkg1/src").IThing;
+export declare function fn4(): import("@fluentui/pkg1").IThing;
 
 
 //// [/src/packages/pkg2/lib/src/index.js]
@@ -139,7 +139,7 @@ exports.fn4 = fn4;
       },
       "../src/index.ts": {
         "version": "8515046367-import { IThings } from '@fluentui/pkg1';\nexport function fn4() {\n  const a: IThings = { thing1: { a: 'b' } };\n  return a.thing1;\n}",
-        "signature": "-10018297277-export declare function fn4(): import(\"../../pkg1/src\").IThing;\r\n",
+        "signature": "-9447422063-export declare function fn4(): import(\"@fluentui/pkg1\").IThing;\r\n",
         "affectsGlobalScope": false
       }
     },