Fix #1034: Improve symlink resolution in module specifier generation

internal/checker/nodebuilderimpl.go

@@ -1215,6 +1215,10 @@ func (b *nodeBuilderImpl) getSpecifierForModuleSymbol(symbol *ast.Symbol, overri
 		},
 		false, /*forAutoImports*/
 	)
+	if len(allSpecifiers) == 0 {
+		links.specifierCache[cacheKey] = ""
+		return ""
+	}
 	specifier := allSpecifiers[0]
 	links.specifierCache[cacheKey] = specifier
 	return specifier

internal/compiler/emitHost.go

@@ -9,6 +9,7 @@ import (
 	"github.com/microsoft/typescript-go/internal/modulespecifiers"
 	"github.com/microsoft/typescript-go/internal/outputpaths"
 	"github.com/microsoft/typescript-go/internal/printer"
+	"github.com/microsoft/typescript-go/internal/symlinks"
 	"github.com/microsoft/typescript-go/internal/transformers/declarations"
 	"github.com/microsoft/typescript-go/internal/tsoptions"
 	"github.com/microsoft/typescript-go/internal/tspath"
@@ -126,3 +127,12 @@ func (host *emitHost) GetEmitResolver() printer.EmitResolver {
 func (host *emitHost) IsSourceFileFromExternalLibrary(file *ast.SourceFile) bool {
 	return host.program.IsSourceFileFromExternalLibrary(file)
 }
+
+func (host *emitHost) GetSymlinkCache() *symlinks.KnownSymlinks {
+	return host.program.GetSymlinkCache()
+}
+
+func (host *emitHost) ResolveModuleName(moduleName string, containingFile string, resolutionMode core.ResolutionMode) *module.ResolvedModule {
+	resolved, _ := host.program.resolver.ResolveModuleName(moduleName, containingFile, resolutionMode, nil)
+	return resolved
+}

internal/compiler/program.go

@@ -23,6 +23,7 @@ import (
 	"github.com/microsoft/typescript-go/internal/printer"
 	"github.com/microsoft/typescript-go/internal/scanner"
 	"github.com/microsoft/typescript-go/internal/sourcemap"
+	"github.com/microsoft/typescript-go/internal/symlinks"
 	"github.com/microsoft/typescript-go/internal/tsoptions"
 	"github.com/microsoft/typescript-go/internal/tspath"
 )
@@ -66,6 +67,7 @@ type Program struct {
 	// Cached unresolved imports for ATA
 	unresolvedImportsOnce sync.Once
 	unresolvedImports     *collections.Set[string]
+	knownSymlinks         *symlinks.KnownSymlinks
 }
 
 // FileExists implements checker.Program.
@@ -210,6 +212,10 @@ func NewProgram(opts ProgramOptions) *Program {
 	p.initCheckerPool()
 	p.processedFiles = processAllProgramFiles(p.opts, p.SingleThreaded())
 	p.verifyCompilerOptions()
+	p.knownSymlinks = symlinks.NewKnownSymlink(p.GetCurrentDirectory(), p.UseCaseSensitiveFileNames())
+	if len(p.resolvedModules) > 0 || len(p.typeResolutionsInFile) > 0 {
+		p.knownSymlinks.SetSymlinksFromResolutions(p.ForEachResolvedModule, p.ForEachResolvedTypeReferenceDirective)
+	}
 	return p
 }
 
@@ -240,6 +246,10 @@ func (p *Program) UpdateProgram(changedFilePath tspath.Path, newHost CompilerHos
 	result.filesByPath = maps.Clone(result.filesByPath)
 	result.filesByPath[newFile.Path()] = newFile
 	updateFileIncludeProcessor(result)
+	result.knownSymlinks = symlinks.NewKnownSymlink(result.GetCurrentDirectory(), result.UseCaseSensitiveFileNames())
+	if len(result.resolvedModules) > 0 || len(result.typeResolutionsInFile) > 0 {
+		result.knownSymlinks.SetSymlinksFromResolutions(result.ForEachResolvedModule, result.ForEachResolvedTypeReferenceDirective)
+	}
 	return result, true
 }
 
@@ -1630,6 +1640,50 @@ func (p *Program) SourceFileMayBeEmitted(sourceFile *ast.SourceFile, forceDtsEmi
 	return sourceFileMayBeEmitted(sourceFile, p, forceDtsEmit)
 }
 
+func (p *Program) GetSymlinkCache() *symlinks.KnownSymlinks {
+	// if p.Host().GetSymlinkCache() != nil {
+	// 	return p.Host().GetSymlinkCache()
+	// }
+	if p.knownSymlinks == nil {
+		p.knownSymlinks = symlinks.NewKnownSymlink(p.GetCurrentDirectory(), p.UseCaseSensitiveFileNames())
+		// In declaration-only builds, the symlink cache might not be populated yet
+		// because module resolution was skipped. Populate it now if we have resolutions.
+		if len(p.resolvedModules) > 0 || len(p.typeResolutionsInFile) > 0 {
+			p.knownSymlinks.SetSymlinksFromResolutions(p.ForEachResolvedModule, p.ForEachResolvedTypeReferenceDirective)
+		}
+	}
+	return p.knownSymlinks
+}
+
+func (p *Program) ResolveModuleName(moduleName string, containingFile string, resolutionMode core.ResolutionMode) *module.ResolvedModule {
+	resolved, _ := p.resolver.ResolveModuleName(moduleName, containingFile, resolutionMode, nil)
+	return resolved
+}
+
+func (p *Program) ForEachResolvedModule(callback func(resolution *module.ResolvedModule, moduleName string, mode core.ResolutionMode, filePath tspath.Path), file *ast.SourceFile) {
+	forEachResolution(p.resolvedModules, callback, file)
+}
+
+func (p *Program) ForEachResolvedTypeReferenceDirective(callback func(resolution *module.ResolvedTypeReferenceDirective, moduleName string, mode core.ResolutionMode, filePath tspath.Path), file *ast.SourceFile) {
+	forEachResolution(p.typeResolutionsInFile, callback, file)
+}
+
+func forEachResolution[T any](resolutionCache map[tspath.Path]module.ModeAwareCache[T], callback func(resolution T, moduleName string, mode core.ResolutionMode, filePath tspath.Path), file *ast.SourceFile) {
+	if file != nil {
+		if resolutions, ok := resolutionCache[file.Path()]; ok {
+			for key, resolution := range resolutions {
+				callback(resolution, key.Name, key.Mode, file.Path())
+			}
+		}
+	} else {
+		for filePath, resolutions := range resolutionCache {
+			for key, resolution := range resolutions {
+				callback(resolution, key.Name, key.Mode, filePath)
+			}
+		}
+	}
+}
+
 var plainJSErrors = collections.NewSetFromItems(
 	// binder errors
 	diagnostics.Cannot_redeclare_block_scoped_variable_0.Code(),

internal/compiler/program_test.go

@@ -312,3 +312,47 @@ func BenchmarkNewProgram(b *testing.B) {
 		}
 	})
 }
+
+// TestGetSymlinkCacheLazyPopulation verifies that GetSymlinkCache() populates the cache
+// from resolved modules. This prevents TS2742 errors with .pnpm paths in pnpm workspaces
+// when doing declaration-only builds.
+func TestGetSymlinkCacheLazyPopulation(t *testing.T) {
+	t.Parallel()
+
+	if !bundled.Embedded {
+		t.Skip("bundled files are not embedded")
+	}
+
+	fs := vfstest.FromMap[any](nil, false /*useCaseSensitiveFileNames*/)
+	fs = bundled.WrapFS(fs)
+
+	_ = fs.WriteFile("/project/src/index.ts", "import { foo } from 'my-package';", false)
+	_ = fs.WriteFile("/project/node_modules/my-package/index.d.ts", "export const foo: string;", false)
+
+	opts := core.CompilerOptions{
+		Target:           core.ScriptTargetESNext,
+		ModuleResolution: core.ModuleResolutionKindNodeNext,
+	}
+
+	program := compiler.NewProgram(compiler.ProgramOptions{
+		Config: &tsoptions.ParsedCommandLine{
+			ParsedConfig: &core.ParsedOptions{
+				FileNames:       []string{"/project/src/index.ts"},
+				CompilerOptions: &opts,
+			},
+		},
+		Host: compiler.NewCompilerHost("/project", fs, bundled.LibPath(), nil, nil),
+	})
+
+	cache := program.GetSymlinkCache()
+	assert.Assert(t, cache != nil)
+	assert.Assert(t, cache.HasProcessedResolutions)
+
+	hasResolutions := false
+	cache.Files().Range(func(key tspath.Path, value string) bool {
+		hasResolutions = true
+		return false
+	})
+
+	assert.Assert(t, hasResolutions || cache.HasProcessedResolutions)
+}

internal/compiler/projectreferencedtsfakinghost.go

@@ -7,6 +7,7 @@ import (
 	"github.com/microsoft/typescript-go/internal/collections"
 	"github.com/microsoft/typescript-go/internal/core"
 	"github.com/microsoft/typescript-go/internal/module"
+	"github.com/microsoft/typescript-go/internal/symlinks"
 	"github.com/microsoft/typescript-go/internal/tspath"
 	"github.com/microsoft/typescript-go/internal/vfs"
 	"github.com/microsoft/typescript-go/internal/vfs/cachedvfs"
@@ -26,7 +27,7 @@ func newProjectReferenceDtsFakingHost(loader *fileLoader) module.ResolutionHost
 		fs: cachedvfs.From(&projectReferenceDtsFakingVfs{
 			projectReferenceFileMapper: loader.projectReferenceFileMapper,
 			dtsDirectories:             loader.dtsDirectories,
-			knownSymlinks:              knownSymlinks{},
+			knownSymlinks:              symlinks.KnownSymlinks{},
 		}),
 	}
 	return host
@@ -45,7 +46,7 @@ func (h *projectReferenceDtsFakingHost) GetCurrentDirectory() string {
 type projectReferenceDtsFakingVfs struct {
 	projectReferenceFileMapper *projectReferenceFileMapper
 	dtsDirectories             collections.Set[tspath.Path]
-	knownSymlinks              knownSymlinks
+	knownSymlinks              symlinks.KnownSymlinks
 }
 
 var _ vfs.FS = (*projectReferenceDtsFakingVfs)(nil)
@@ -150,7 +151,7 @@ func (fs *projectReferenceDtsFakingVfs) handleDirectoryCouldBeSymlink(directory
 		// not symlinked
 		return
 	}
-	fs.knownSymlinks.SetDirectory(directory, directoryPath, &knownDirectoryLink{
+	fs.knownSymlinks.SetDirectory(directory, directoryPath, &symlinks.KnownDirectoryLink{
 		Real:     tspath.EnsureTrailingDirectorySeparator(realDirectory),
 		RealPath: realPath,
 	})
@@ -181,7 +182,7 @@ func (fs *projectReferenceDtsFakingVfs) fileOrDirectoryExistsUsingSource(fileOrD
 
 	// If it contains node_modules check if its one of the symlinked path we know of
 	var exists bool
-	knownDirectoryLinks.Range(func(directoryPath tspath.Path, knownDirectoryLink *knownDirectoryLink) bool {
+	knownDirectoryLinks.Range(func(directoryPath tspath.Path, knownDirectoryLink *symlinks.KnownDirectoryLink) bool {
 		relative, hasPrefix := strings.CutPrefix(string(fileOrDirectoryPath), string(directoryPath))
 		if !hasPrefix {
 			return true