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Elide Unused Re-exports In TSServer #40966

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Elide Unused Re-exports In TSServer #40966

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94 changes: 89 additions & 5 deletions src/compiler/program.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2372,7 +2372,7 @@ namespace ts {
}

// Get source file from normalized fileName
function findSourceFile(fileName: string, path: Path, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, refFile: RefFile | undefined, packageId: PackageId | undefined): SourceFile | undefined {
function findSourceFile(fileName: string, path: Path, isDefaultLib: boolean, ignoreNoDefaultLib: boolean, refFile: RefFile | undefined, packageId: PackageId | undefined, identifersToImport?: ReadonlySet<__String>): SourceFile | undefined {
if (useSourceOfProjectReferenceRedirect) {
let source = getSourceOfProjectReferenceRedirect(fileName);
// If preserveSymlinks is true, module resolution wont jump the symlink
Expand All @@ -2389,7 +2389,7 @@ namespace ts {
}
if (source) {
const file = isString(source) ?
findSourceFile(source, toPath(source), isDefaultLib, ignoreNoDefaultLib, refFile, packageId) :
findSourceFile(source, toPath(source), isDefaultLib, ignoreNoDefaultLib, refFile, packageId, identifersToImport) :
undefined;
if (file) addFileToFilesByName(file, path, /*redirectedPath*/ undefined);
return file;
Expand Down Expand Up @@ -2526,7 +2526,7 @@ namespace ts {


// always process imported modules to record module name resolutions
processImportedModules(file);
processImportedModules(file, identifersToImport);

if (isDefaultLib) {
processingDefaultLibFiles!.push(file);
Expand Down Expand Up @@ -2853,13 +2853,15 @@ namespace ts {
return host.getCanonicalFileName(fileName);
}

function processImportedModules(file: SourceFile) {
function processImportedModules(file: SourceFile, identifiersToImport?: ReadonlySet<__String>) {
collectExternalModuleReferences(file);
if (file.imports.length || file.moduleAugmentations.length) {
// Because global augmentation doesn't have string literal name, we can check for global augmentation as such.
const moduleNames = getModuleNames(file);
const unusedModuleNames = getUnusedModuleNames(file, identifiersToImport);
const resolutions = resolveModuleNamesReusingOldState(moduleNames, file);
Debug.assert(resolutions.length === moduleNames.length);
const moduleNamesToImportSymbols = mapModuleNamesToImportSymbols(file);
for (let i = 0; i < moduleNames.length; i++) {
const resolution = resolutions[i];
setResolvedModule(file, moduleNames[i], resolution);
Expand All @@ -2877,6 +2879,8 @@ namespace ts {
currentNodeModulesDepth++;
}

const isModuleUnused = unusedModuleNames.has(moduleNames[i]);

// add file to program only if:
// - resolution was successful
// - noResolve is falsy
Expand All @@ -2890,6 +2894,7 @@ namespace ts {
&& !options.noResolve
&& i < file.imports.length
&& !elideImport
&& !isModuleUnused
&& !(isJsFile && !getAllowJSCompilerOption(options))
&& (isInJSFile(file.imports[i]) || !(file.imports[i].flags & NodeFlags.JSDoc));

Expand All @@ -2899,6 +2904,7 @@ namespace ts {
else if (shouldAddFile) {
const path = toPath(resolvedFileName);
const pos = skipTrivia(file.text, file.imports[i].pos);
const importSymbols = moduleNamesToImportSymbols.get(moduleNames[i]);
findSourceFile(
resolvedFileName,
path,
Expand All @@ -2911,7 +2917,10 @@ namespace ts {
pos,
end: file.imports[i].end
},
resolution.packageId
resolution.packageId,
importSymbols && identifiersToImport
? intersect(importSymbols, identifiersToImport)
: (importSymbols || identifiersToImport)
);
}

Expand Down Expand Up @@ -3857,4 +3866,79 @@ namespace ts {
}
return res;
}

function getUnusedModuleNames(file: SourceFile, identifiersToImport?: ReadonlySet<__String>): Set<string> {
if (identifiersToImport === undefined) {
return new Set();
}

const unusedModuleNames: Set<string> = new Set();

for (const statement of file.statements) {
if (!isExportDeclaration(statement)) {
break;
}

if (statement.moduleSpecifier?.kind !== SyntaxKind.StringLiteral) {
break;
}
const moduleSpecifier = statement.moduleSpecifier as StringLiteral;

const exportClause = statement.exportClause;
if (!exportClause) {
break;
}

if (!isNamedExports(exportClause)) {
break;
}

const isExportClauseUsed = exportClause.elements.some(element => {
const identifier = element.propertyName ?? element.name;
return identifiersToImport.has(identifier.escapedText);
});

if (!isExportClauseUsed) {
unusedModuleNames.add(moduleSpecifier.text);
}
}

return unusedModuleNames;
}

function mapModuleNamesToImportSymbols(file: SourceFile): Map<Set<__String>> {
const moduleNamesToImportSymbols = new Map<string, Set<__String>>();
for (const statement of file.statements) {
if (statement.kind !== SyntaxKind.ImportDeclaration) {
break;
}

const importDeclaration = statement as ImportDeclaration;
if (importDeclaration.moduleSpecifier.kind !== SyntaxKind.StringLiteral) {
break;
}
const moduleSpecifier = importDeclaration.moduleSpecifier as StringLiteral;

const importSymbols = moduleNamesToImportSymbols.get(moduleSpecifier.text) ?? new Set();
const namedBindings = importDeclaration.importClause?.namedBindings;

if (namedBindings?.kind !== SyntaxKind.NamedImports) {
break;
}
const namedImports = namedBindings.elements;

for (const binding of namedImports) {
const identifier = binding.propertyName ?? binding.name;
importSymbols.add(identifier.escapedText);
}

moduleNamesToImportSymbols.set(moduleSpecifier.text, importSymbols);
}

return moduleNamesToImportSymbols;
}

function intersect<T>(a: ReadonlySet<T>, b: ReadonlySet<T>): ReadonlySet<T> {
return new Set(Array.from(a as unknown as Iterable<T>).filter(el => b.has(el)));
}
}