Update type-only import semantics to allow type queries

src/compiler/commandLineParser.ts

@@ -475,9 +475,9 @@ namespace ts {
         {
             name: "importsNotUsedAsValues",
             type: createMapFromTemplate({
-                remove: importsNotUsedAsValues.Remove,
-                preserve: importsNotUsedAsValues.Preserve,
-                error: importsNotUsedAsValues.Error
+                remove: ImportsNotUsedAsValues.Remove,
+                preserve: ImportsNotUsedAsValues.Preserve,
+                error: ImportsNotUsedAsValues.Error
             }),
             affectsEmit: true,
             affectsSemanticDiagnostics: true,

src/compiler/diagnosticMessages.json

@@ -1055,11 +1055,15 @@
         "category": "Error",
         "code": 1359
     },
-    "Type-only {0} must reference a type, but '{1}' is a value.": {
+    "Did you mean to parenthesize this function type?": {
+        "category": "Error",
+        "code": 1360
+    },
+    "'{0}' cannot be used as a value because it was imported using 'import type'.": {
         "category": "Error",
         "code": 1361
     },
-    "Enum '{0}' cannot be used as a value because only its type has been imported.": {
+    "'{0}' cannot be used as a value because it was exported using 'export type'.": {
         "category": "Error",
         "code": 1362
     },
@@ -1099,10 +1103,6 @@
         "category": "Error",
         "code": 1371
     },
-    "This import may be converted to a type-only import.": {
-        "category": "Suggestion",
-        "code": 1372
-    },
     "Convert to type-only import": {
         "category": "Message",
         "code": 1373
@@ -1115,9 +1115,17 @@
         "category": "Error",
         "code": 1375
     },
+    "'{0}' was imported here.": {
+        "category": "Message",
+        "code": 1376
+    },
+    "'{0}' was exported here.": {
+        "category": "Message",
+        "code": 1377
+    },
     "Top-level 'await' expressions are only allowed when the 'module' option is set to 'esnext' or 'system', and the 'target' option is set to 'es2017' or higher.": {
         "category": "Error",
-        "code": 1376
+        "code": 1378
     },
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",

src/compiler/transformers/ts.ts

@@ -2778,8 +2778,8 @@ namespace ts {
             // Elide the declaration if the import clause was elided.
             const importClause = visitNode(node.importClause, visitImportClause, isImportClause);
             return importClause ||
-                compilerOptions.importsNotUsedAsValues === importsNotUsedAsValues.Preserve ||
-                compilerOptions.importsNotUsedAsValues === importsNotUsedAsValues.Error
+                compilerOptions.importsNotUsedAsValues === ImportsNotUsedAsValues.Preserve ||
+                compilerOptions.importsNotUsedAsValues === ImportsNotUsedAsValues.Error
                 ? updateImportDeclaration(
                     node,
                     /*decorators*/ undefined,
@@ -2931,7 +2931,7 @@ namespace ts {
             if (isExternalModuleImportEqualsDeclaration(node)) {
                 const isReferenced = resolver.isReferencedAliasDeclaration(node);
                 // If the alias is unreferenced but we want to keep the import, replace with 'import "mod"'.
-                if (!isReferenced && compilerOptions.importsNotUsedAsValues === importsNotUsedAsValues.Preserve) {
+                if (!isReferenced && compilerOptions.importsNotUsedAsValues === ImportsNotUsedAsValues.Preserve) {
                     return setOriginalNode(
                         setTextRange(
                             createImportDeclaration(

src/compiler/types.ts

@@ -2538,6 +2538,7 @@ namespace ts {
     }
 
     export type ImportOrExportSpecifier = ImportSpecifier | ExportSpecifier;
+    export type TypeOnlyCompatibleAliasDeclaration = ImportClause | NamespaceImport | ImportOrExportSpecifier;
 
     /**
      * This is either an `export =` or an `export default` declaration.
@@ -4062,7 +4063,8 @@ namespace ts {
         instantiations?: Map<Type>;                 // Instantiations of generic type alias (undefined if non-generic)
         inferredClassSymbol?: Map<TransientSymbol>; // Symbol of an inferred ES5 constructor function
         mapper?: TypeMapper;                        // Type mapper for instantiation alias
-        referenced?: boolean;                       // True if alias symbol has been referenced as a value
+        referenced?: boolean;                       // True if alias symbol has been referenced as a value that can be emitted
+        constEnumReferenced?: boolean;              // True if alias symbol resolves to a const enum and is referenced as a value ('referenced' will be false)
         containingType?: UnionOrIntersectionType;   // Containing union or intersection type for synthetic property
         leftSpread?: Symbol;                        // Left source for synthetic spread property
         rightSpread?: Symbol;                       // Right source for synthetic spread property
@@ -4085,6 +4087,7 @@ namespace ts {
         deferralConstituents?: Type[];      // Calculated list of constituents for a deferred type
         deferralParent?: Type;              // Source union/intersection of a deferred type
         cjsExportMerged?: Symbol;           // Version of the symbol with all non export= exports merged with the export= target
+        typeOnlyDeclaration?: TypeOnlyCompatibleAliasDeclaration | false; // First resolved alias declaration that makes the symbol only usable in type constructs
     }
 
     /* @internal */
@@ -5046,7 +5049,7 @@ namespace ts {
         /*@internal*/generateCpuProfile?: string;
         /*@internal*/help?: boolean;
         importHelpers?: boolean;
-        importsNotUsedAsValues?: importsNotUsedAsValues;
+        importsNotUsedAsValues?: ImportsNotUsedAsValues;
         /*@internal*/init?: boolean;
         inlineSourceMap?: boolean;
         inlineSources?: boolean;
@@ -5168,7 +5171,7 @@ namespace ts {
         ReactNative = 3
     }
 
-    export const enum importsNotUsedAsValues {
+    export const enum ImportsNotUsedAsValues {
         Remove,
         Preserve,
         Error

src/compiler/utilities.ts

@@ -44,14 +44,6 @@ namespace ts {
         return (symbol.flags & SymbolFlags.Transient) !== 0;
     }
 
-    export function isTypeOnlyAlias(symbol: Symbol): symbol is TransientSymbol & { immediateTarget: Symbol } {
-        return isTransientSymbol(symbol) && !!symbol.immediateTarget;
-    }
-
-    export function isTypeOnlyEnumAlias(symbol: Symbol): ReturnType<typeof isTypeOnlyAlias> {
-        return isTypeOnlyAlias(symbol) && !!(symbol.immediateTarget.flags & SymbolFlags.Enum);
-    }
-
     const stringWriter = createSingleLineStringWriter();
 
     function createSingleLineStringWriter(): EmitTextWriter {
@@ -1779,6 +1771,27 @@ namespace ts {
         }
     }
 
+    export function isPartOfTypeQuery(node: Node) {
+        while (node.kind === SyntaxKind.QualifiedName || node.kind === SyntaxKind.Identifier) {
+            node = node.parent;
+        }
+        return node.kind === SyntaxKind.TypeQuery;
+    }
+
+    export function isPartOfPossiblyValidTypeOrAbstractComputedPropertyName(node: Node) {
+        while (node.kind === SyntaxKind.Identifier || node.kind === SyntaxKind.PropertyAccessExpression) {
+            node = node.parent;
+        }
+        if (node.kind !== SyntaxKind.ComputedPropertyName) {
+            return false;
+        }
+        if (hasModifier(node.parent, ModifierFlags.Abstract)) {
+            return true;
+        }
+        const containerKind = node.parent.parent.kind;
+        return containerKind === SyntaxKind.InterfaceDeclaration || containerKind === SyntaxKind.TypeLiteral;
+    }
+
     export function isExternalModuleImportEqualsDeclaration(node: Node): node is ImportEqualsDeclaration & { moduleReference: ExternalModuleReference } {
         return node.kind === SyntaxKind.ImportEqualsDeclaration && (<ImportEqualsDeclaration>node).moduleReference.kind === SyntaxKind.ExternalModuleReference;
     }
@@ -2285,6 +2298,19 @@ namespace ts {
         return node.kind === SyntaxKind.ImportDeclaration && !!node.importClause && !!node.importClause.name;
     }
 
+    export function forEachImportClauseDeclaration<T>(node: ImportClause, action: (declaration: ImportClause | NamespaceImport | ImportSpecifier) => T | undefined): T | undefined {
+        if (node.name) {
+            const result = action(node);
+            if (result) return result;
+        }
+        if (node.namedBindings) {
+            const result = isNamespaceImport(node.namedBindings)
+                ? action(node.namedBindings)
+                : forEach(node.namedBindings.elements, action);
+            if (result) return result;
+        }
+    }
+
     export function hasQuestionToken(node: Node) {
         if (node) {
             switch (node.kind) {
@@ -2734,6 +2760,16 @@ namespace ts {
             node.kind === SyntaxKind.PropertyAssignment && isAliasableExpression((node as PropertyAssignment).initializer);
     }
 
+    export function getTypeOnlyCompatibleAliasDeclarationFromName(node: Identifier): TypeOnlyCompatibleAliasDeclaration | undefined {
+        switch (node.parent.kind) {
+            case SyntaxKind.ImportClause:
+            case SyntaxKind.ImportSpecifier:
+            case SyntaxKind.NamespaceImport:
+            case SyntaxKind.ExportSpecifier:
+                return node.parent as TypeOnlyCompatibleAliasDeclaration;
+        }
+    }
+
     function isAliasableExpression(e: Expression) {
         return isEntityNameExpression(e) || isClassExpression(e);
     }

src/compiler/utilitiesPublic.ts

@@ -1721,16 +1721,15 @@ namespace ts {
         return isImportSpecifier(node) || isExportSpecifier(node);
     }
 
-    export function isTypeOnlyImportOrExportName(node: Node): boolean {
-        if (node.kind !== SyntaxKind.Identifier) {
-            return false;
-        }
-        switch (node.parent.kind) {
+    export function isTypeOnlyImportOrExportDeclaration(node: Node): node is TypeOnlyCompatibleAliasDeclaration {
+        switch (node.kind) {
             case SyntaxKind.ImportSpecifier:
             case SyntaxKind.ExportSpecifier:
-                return (node.parent as ImportSpecifier | ExportSpecifier).parent.parent.isTypeOnly;
+                return (node as ImportOrExportSpecifier).parent.parent.isTypeOnly;
+            case SyntaxKind.NamespaceImport:
+                return (node as NamespaceImport).parent.isTypeOnly;
             case SyntaxKind.ImportClause:
-                return (node.parent as ImportClause).isTypeOnly;
+                return (node as ImportClause).isTypeOnly;
             default:
                 return false;
         }

src/services/symbolDisplay.ts

@@ -2,10 +2,6 @@
 namespace ts.SymbolDisplay {
     // TODO(drosen): use contextual SemanticMeaning.
     export function getSymbolKind(typeChecker: TypeChecker, symbol: Symbol, location: Node): ScriptElementKind {
-        while (isTypeOnlyAlias(symbol)) {
-            symbol = symbol.immediateTarget;
-        }
-
         const result = getSymbolKindOfConstructorPropertyMethodAccessorFunctionOrVar(typeChecker, symbol, location);
         if (result !== ScriptElementKind.unknown) {
             return result;
@@ -125,11 +121,6 @@ namespace ts.SymbolDisplay {
     // TODO(drosen): Currently completion entry details passes the SemanticMeaning.All instead of using semanticMeaning of location
     export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: TypeChecker, symbol: Symbol, sourceFile: SourceFile, enclosingDeclaration: Node | undefined,
         location: Node, semanticMeaning = getMeaningFromLocation(location), alias?: Symbol): SymbolDisplayPartsDocumentationAndSymbolKind {
-
-        while (isTypeOnlyAlias(symbol)) {
-            symbol = symbol.immediateTarget;
-        }
-
         const displayParts: SymbolDisplayPart[] = [];
         let documentation: SymbolDisplayPart[] = [];
         let tags: JSDocTagInfo[] = [];

tests/baselines/reference/ambient.js

@@ -0,0 +1,25 @@
+//// [tests/cases/conformance/externalModules/typeOnly/ambient.ts] ////
+
+//// [a.ts]
+export class A { a!: string }
+
+//// [b.ts]
+import type { A } from './a';
+declare class B extends A {}
+declare namespace ns {
+  class C extends A {}
+}
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;
+var A = /** @class */ (function () {
+    function A() {
+    }
+    return A;
+}());
+exports.A = A;
+//// [b.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/ambient.symbols

@@ -0,0 +1,21 @@
+=== /a.ts ===
+export class A { a!: string }
+>A : Symbol(A, Decl(a.ts, 0, 0))
+>a : Symbol(A.a, Decl(a.ts, 0, 16))
+
+=== /b.ts ===
+import type { A } from './a';
+>A : Symbol(A, Decl(b.ts, 0, 13))
+
+declare class B extends A {}
+>B : Symbol(B, Decl(b.ts, 0, 29))
+>A : Symbol(A, Decl(b.ts, 0, 13))
+
+declare namespace ns {
+>ns : Symbol(ns, Decl(b.ts, 1, 28))
+
+  class C extends A {}
+>C : Symbol(C, Decl(b.ts, 2, 22))
+>A : Symbol(A, Decl(b.ts, 0, 13))
+}
+

tests/baselines/reference/ambient.types

@@ -0,0 +1,21 @@
+=== /a.ts ===
+export class A { a!: string }
+>A : A
+>a : string
+
+=== /b.ts ===
+import type { A } from './a';
+>A : A
+
+declare class B extends A {}
+>B : B
+>A : A
+
+declare namespace ns {
+>ns : typeof ns
+
+  class C extends A {}
+>C : C
+>A : A
+}
+

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -1547,6 +1547,7 @@ declare namespace ts {
         name: Identifier;
     }
     export type ImportOrExportSpecifier = ImportSpecifier | ExportSpecifier;
+    export type TypeOnlyCompatibleAliasDeclaration = ImportClause | NamespaceImport | ImportOrExportSpecifier;
     /**
      * This is either an `export =` or an `export default` declaration.
      * Unless `isExportEquals` is set, this node was parsed as an `export default`.
@@ -2651,7 +2652,7 @@ declare namespace ts {
         experimentalDecorators?: boolean;
         forceConsistentCasingInFileNames?: boolean;
         importHelpers?: boolean;
-        importsNotUsedAsValues?: importsNotUsedAsValues;
+        importsNotUsedAsValues?: ImportsNotUsedAsValues;
         inlineSourceMap?: boolean;
         inlineSources?: boolean;
         isolatedModules?: boolean;
@@ -2750,7 +2751,7 @@ declare namespace ts {
         React = 2,
         ReactNative = 3
     }
-    export enum importsNotUsedAsValues {
+    export enum ImportsNotUsedAsValues {
         Remove = 0,
         Preserve = 1,
         Error = 2
@@ -3739,7 +3740,7 @@ declare namespace ts {
     function isTemplateLiteralToken(node: Node): node is TemplateLiteralToken;
     function isTemplateMiddleOrTemplateTail(node: Node): node is TemplateMiddle | TemplateTail;
     function isImportOrExportSpecifier(node: Node): node is ImportSpecifier | ExportSpecifier;
-    function isTypeOnlyImportOrExportName(node: Node): boolean;
+    function isTypeOnlyImportOrExportDeclaration(node: Node): node is TypeOnlyCompatibleAliasDeclaration;
     function isStringTextContainingNode(node: Node): node is StringLiteral | TemplateLiteralToken;
     function isModifier(node: Node): node is Modifier;
     function isEntityName(node: Node): node is EntityName;

tests/baselines/reference/api/typescript.d.ts

@@ -1547,6 +1547,7 @@ declare namespace ts {
         name: Identifier;
     }
     export type ImportOrExportSpecifier = ImportSpecifier | ExportSpecifier;
+    export type TypeOnlyCompatibleAliasDeclaration = ImportClause | NamespaceImport | ImportOrExportSpecifier;
     /**
      * This is either an `export =` or an `export default` declaration.
      * Unless `isExportEquals` is set, this node was parsed as an `export default`.
@@ -2651,7 +2652,7 @@ declare namespace ts {
         experimentalDecorators?: boolean;
         forceConsistentCasingInFileNames?: boolean;
         importHelpers?: boolean;
-        importsNotUsedAsValues?: importsNotUsedAsValues;
+        importsNotUsedAsValues?: ImportsNotUsedAsValues;
         inlineSourceMap?: boolean;
         inlineSources?: boolean;
         isolatedModules?: boolean;
@@ -2750,7 +2751,7 @@ declare namespace ts {
         React = 2,
         ReactNative = 3
     }
-    export enum importsNotUsedAsValues {
+    export enum ImportsNotUsedAsValues {
         Remove = 0,
         Preserve = 1,
         Error = 2
@@ -3739,7 +3740,7 @@ declare namespace ts {
     function isTemplateLiteralToken(node: Node): node is TemplateLiteralToken;
     function isTemplateMiddleOrTemplateTail(node: Node): node is TemplateMiddle | TemplateTail;
     function isImportOrExportSpecifier(node: Node): node is ImportSpecifier | ExportSpecifier;
-    function isTypeOnlyImportOrExportName(node: Node): boolean;
+    function isTypeOnlyImportOrExportDeclaration(node: Node): node is TypeOnlyCompatibleAliasDeclaration;
     function isStringTextContainingNode(node: Node): node is StringLiteral | TemplateLiteralToken;
     function isModifier(node: Node): node is Modifier;
     function isEntityName(node: Node): node is EntityName;