Fix type-only imports in interface 'extends' and import=/export=

src/compiler/checker.ts

@@ -2182,9 +2182,32 @@ namespace ts {
 
         function getTargetOfImportEqualsDeclaration(node: ImportEqualsDeclaration, dontResolveAlias: boolean): Symbol | undefined {
             if (node.moduleReference.kind === SyntaxKind.ExternalModuleReference) {
-                return resolveExternalModuleSymbol(resolveExternalModuleName(node, getExternalModuleImportEqualsDeclarationExpression(node)));
+                const immediate = resolveExternalModuleName(node, getExternalModuleImportEqualsDeclarationExpression(node));
+                const resolved = resolveExternalModuleSymbol(immediate);
+                if (!markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, immediate)) {
+                    markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved);
+                }
+                return resolved;
+            }
+            const resolved = getSymbolOfPartOfRightHandSideOfImportEquals(node.moduleReference, dontResolveAlias);
+            checkAndReportErrorForResolvingImportAliasToTypeOnlySymbol(node, resolved);
+            return resolved;
+        }
+
+        function checkAndReportErrorForResolvingImportAliasToTypeOnlySymbol(node: ImportEqualsDeclaration, resolved: Symbol | undefined) {
+            if (markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved)) {
+                const typeOnlyDeclaration = getTypeOnlyAliasDeclaration(getSymbolOfNode(node))!;
+                const message = typeOnlyDeclaration.kind === SyntaxKind.ExportSpecifier
+                    ? Diagnostics.An_import_alias_cannot_reference_a_declaration_that_was_exported_using_export_type
+                    : Diagnostics.An_import_alias_cannot_reference_a_declaration_that_was_imported_using_import_type;
+                const relatedMessage = typeOnlyDeclaration.kind === SyntaxKind.ExportSpecifier
+                    ? Diagnostics._0_was_exported_here
+                    : Diagnostics._0_was_imported_here;
+                // Non-null assertion is safe because the optionality comes from ImportClause,
+                // but if an ImportClause was the typeOnlyDeclaration, it had to have a `name`.
+                const name = unescapeLeadingUnderscores(typeOnlyDeclaration.name!.escapedText);
+                addRelatedInfo(error(node.moduleReference, message), createDiagnosticForNode(typeOnlyDeclaration, relatedMessage, name));
             }
-            return getSymbolOfPartOfRightHandSideOfImportEquals(node.moduleReference, dontResolveAlias);
         }
 
         function resolveExportByName(moduleSymbol: Symbol, name: __String, sourceNode: TypeOnlyCompatibleAliasDeclaration | undefined, dontResolveAlias: boolean) {
@@ -2193,8 +2216,11 @@ namespace ts {
                 return getPropertyOfType(getTypeOfSymbol(exportValue), name);
             }
             const exportSymbol = moduleSymbol.exports!.get(name);
-            markSymbolOfAliasDeclarationIfResolvesToTypeOnly(sourceNode, exportSymbol);
-            return resolveSymbol(exportSymbol, dontResolveAlias);
+            const resolved = resolveSymbol(exportSymbol, dontResolveAlias);
+            if (!markSymbolOfAliasDeclarationIfResolvesToTypeOnly(sourceNode, exportSymbol)) {
+                markSymbolOfAliasDeclarationIfResolvesToTypeOnly(sourceNode, resolved);
+            }
+            return resolved;
         }
 
         function isSyntacticDefault(node: Node) {
@@ -2234,7 +2260,7 @@ namespace ts {
 
         function getTargetOfImportClause(node: ImportClause, dontResolveAlias: boolean): Symbol | undefined {
             const moduleSymbol = resolveExternalModuleName(node, node.parent.moduleSpecifier);
-            markSymbolOfAliasDeclarationIfTypeOnly(node);
+            const isTypeOnly = markSymbolOfAliasDeclarationIfTypeOnly(node);
 
             if (moduleSymbol) {
                 let exportDefaultSymbol: Symbol | undefined;
@@ -2277,16 +2303,26 @@ namespace ts {
                 }
                 else if (hasSyntheticDefault) {
                     // per emit behavior, a synthetic default overrides a "real" .default member if `__esModule` is not present
-                    return resolveExternalModuleSymbol(moduleSymbol, dontResolveAlias) || resolveSymbol(moduleSymbol, dontResolveAlias);
+                    const resolved = resolveExternalModuleSymbol(moduleSymbol, dontResolveAlias) || resolveSymbol(moduleSymbol, dontResolveAlias);
+                    if (!isTypeOnly && !markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, moduleSymbol)) {
+                        markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved);
+                    }
+                    return resolved;
                 }
+                if (!isTypeOnly) markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, exportDefaultSymbol);
                 return exportDefaultSymbol;
             }
         }
 
         function getTargetOfNamespaceImport(node: NamespaceImport, dontResolveAlias: boolean): Symbol | undefined {
             const moduleSpecifier = node.parent.parent.moduleSpecifier;
-            markSymbolOfAliasDeclarationIfTypeOnly(node);
-            return resolveESModuleSymbol(resolveExternalModuleName(node, moduleSpecifier), moduleSpecifier, dontResolveAlias, /*suppressUsageError*/ false);
+            const isTypeOnly = markSymbolOfAliasDeclarationIfTypeOnly(node);
+            const immediate = resolveExternalModuleName(node, moduleSpecifier);
+            const resolved = resolveESModuleSymbol(immediate, moduleSpecifier, dontResolveAlias, /*suppressUsageError*/ false);
+            if (!isTypeOnly && !markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, immediate)) {
+                markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved);
+            }
+            return resolved;
         }
 
         function getTargetOfNamespaceExport(node: NamespaceExport, dontResolveAlias: boolean): Symbol | undefined {
@@ -2332,8 +2368,11 @@ namespace ts {
             if (symbol.flags & SymbolFlags.Module) {
                 const name = (specifier.propertyName ?? specifier.name).escapedText;
                 const exportSymbol = getExportsOfSymbol(symbol).get(name);
-                markSymbolOfAliasDeclarationIfResolvesToTypeOnly(specifier, exportSymbol);
-                return resolveSymbol(exportSymbol, dontResolveAlias);
+                const resolved = resolveSymbol(exportSymbol, dontResolveAlias);
+                if (!markSymbolOfAliasDeclarationIfResolvesToTypeOnly(specifier, exportSymbol)) {
+                    markSymbolOfAliasDeclarationIfResolvesToTypeOnly(specifier, resolved);
+                }
+                return resolved;
             }
         }
 
@@ -2433,24 +2472,30 @@ namespace ts {
         }
 
         function getTargetOfImportSpecifier(node: ImportSpecifier, dontResolveAlias: boolean): Symbol | undefined {
-            markSymbolOfAliasDeclarationIfTypeOnly(node);
-            return getExternalModuleMember(node.parent.parent.parent, node, dontResolveAlias);
+            const isTypeOnly = markSymbolOfAliasDeclarationIfTypeOnly(node);
+            const resolved = getExternalModuleMember(node.parent.parent.parent, node, dontResolveAlias);
+            if (!isTypeOnly) markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved);
+            return resolved;
         }
 
         function getTargetOfNamespaceExportDeclaration(node: NamespaceExportDeclaration, dontResolveAlias: boolean): Symbol {
             return resolveExternalModuleSymbol(node.parent.symbol, dontResolveAlias);
         }
 
         function getTargetOfExportSpecifier(node: ExportSpecifier, meaning: SymbolFlags, dontResolveAlias?: boolean) {
-            markSymbolOfAliasDeclarationIfTypeOnly(node);
-            return node.parent.parent.moduleSpecifier ?
+            const isTypeOnly = markSymbolOfAliasDeclarationIfTypeOnly(node);
+            const resolved = node.parent.parent.moduleSpecifier ?
                 getExternalModuleMember(node.parent.parent, node, dontResolveAlias) :
                 resolveEntityName(node.propertyName || node.name, meaning, /*ignoreErrors*/ false, dontResolveAlias);
+            if (!isTypeOnly) markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved);
+            return resolved;
         }
 
         function getTargetOfExportAssignment(node: ExportAssignment | BinaryExpression, dontResolveAlias: boolean): Symbol | undefined {
             const expression = (isExportAssignment(node) ? node.expression : node.right) as EntityNameExpression | ClassExpression;
-            return getTargetOfAliasLikeExpression(expression, dontResolveAlias);
+            const resolved = getTargetOfAliasLikeExpression(expression, dontResolveAlias);
+            markSymbolOfAliasDeclarationIfResolvesToTypeOnly(node, resolved);
+            return resolved;
         }
 
         function getTargetOfAliasLikeExpression(expression: Expression, dontResolveAlias: boolean) {
@@ -2547,22 +2592,38 @@ namespace ts {
             return links.target;
         }
 
-        function markSymbolOfAliasDeclarationIfResolvesToTypeOnly(aliasDeclaration: TypeOnlyCompatibleAliasDeclaration | undefined, resolvesToSymbol: Symbol | undefined) {
-            if (!aliasDeclaration || !resolvesToSymbol) return;
+        /**
+         * If an alias symbol is not itself marked type-only, but resolves to a type-only alias
+         * somewhere in its resolution chain, save a reference to the type-only alias declaration
+         * so the alias _not_ marked type-only can be identified as _transitively_ type-only.
+         * @param aliasDeclaration The alias declaration not marked as type-only
+         * @param resolvesToSymbol A symbol somewhere in the resolution chain of the alias symbol
+         * @param overwriteEmpty Checks `resolvesToSymbol` for type-only declarations even if `aliasDeclaration`
+         * has already been marked as not resolving to a type-only alias. Used when recursively resolving qualified
+         * names of import aliases, e.g. `import C = a.b.C`. If namespace `a` is not found to be type-only, the
+         * import declaration will initially be marked as not resolving to a type-only symbol. But, namespace `b`
+         * must still be checked for a type-only marker, overwriting the previous negative result if found.
+         */
+        function markSymbolOfAliasDeclarationIfResolvesToTypeOnly(aliasDeclaration: Declaration | undefined, resolvesToSymbol: Symbol | undefined, overwriteEmpty?: boolean): boolean {
+            if (!aliasDeclaration || !resolvesToSymbol) return false;
             const sourceSymbol = getSymbolOfNode(aliasDeclaration);
             const links = getSymbolLinks(sourceSymbol);
-            if (links.typeOnlyDeclaration === undefined) {
-                const typeOnly = find(resolvesToSymbol.declarations, isTypeOnlyImportOrExportDeclaration);
+            if (links.typeOnlyDeclaration === undefined || overwriteEmpty && links.typeOnlyDeclaration === false) {
+                resolvesToSymbol = resolvesToSymbol.exports?.get(InternalSymbolName.ExportEquals) ?? resolvesToSymbol;
+                const typeOnly = resolvesToSymbol.declarations && find(resolvesToSymbol.declarations, isTypeOnlyImportOrExportDeclaration);
                 links.typeOnlyDeclaration = typeOnly ?? getSymbolLinks(resolvesToSymbol).typeOnlyDeclaration ?? false;
             }
+            return !!links.typeOnlyDeclaration;
         }
 
-        function markSymbolOfAliasDeclarationIfTypeOnly(aliasDeclaration: TypeOnlyCompatibleAliasDeclaration) {
+        function markSymbolOfAliasDeclarationIfTypeOnly(aliasDeclaration: TypeOnlyCompatibleAliasDeclaration): boolean {
             if (isTypeOnlyImportOrExportDeclaration(aliasDeclaration)) {
                 const symbol = getSymbolOfNode(aliasDeclaration);
                 const links = getSymbolLinks(symbol);
                 links.typeOnlyDeclaration = aliasDeclaration;
+                return true;
             }
+            return false;
         }
 
         /** Indicates that a symbol directly or indirectly resolves to a type-only import or export. */
@@ -2700,8 +2761,8 @@ namespace ts {
                 throw Debug.assertNever(name, "Unknown entity name kind.");
             }
             Debug.assert((getCheckFlags(symbol) & CheckFlags.Instantiated) === 0, "Should never get an instantiated symbol here.");
-            if (isIdentifier(name) && symbol.flags & SymbolFlags.Alias) {
-                markSymbolOfAliasDeclarationIfResolvesToTypeOnly(getTypeOnlyCompatibleAliasDeclarationFromName(name), symbol);
+            if (isEntityName(name) && (symbol.flags & SymbolFlags.Alias || name.parent.kind === SyntaxKind.ExportAssignment)) {
+                markSymbolOfAliasDeclarationIfResolvesToTypeOnly(getAliasDeclarationFromName(name), symbol, /*overwriteEmpty*/ true);
             }
             return (symbol.flags & meaning) || dontResolveAlias ? symbol : resolveAlias(symbol);
         }

src/compiler/core.ts

@@ -2011,4 +2011,4 @@ namespace ts {
             }
         }
     }
-}
+}

src/compiler/diagnosticMessages.json

@@ -1127,6 +1127,14 @@
         "category": "Error",
         "code": 1378
     },
+    "An import alias cannot reference a declaration that was exported using 'export type'.": {
+        "category": "Error",
+        "code": 1379
+    },
+    "An import alias cannot reference a declaration that was imported using 'import type'.": {
+        "category": "Error",
+        "code": 1380
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",

src/compiler/utilities.ts

@@ -1792,9 +1792,10 @@ namespace ts {
         return containerKind === SyntaxKind.InterfaceDeclaration || containerKind === SyntaxKind.TypeLiteral;
     }
 
-    export function isFirstIdentifierOfImplementsClause(node: Node) {
-        return node.parent?.parent?.parent?.kind === SyntaxKind.HeritageClause
-            && (node.parent.parent.parent as HeritageClause).token === SyntaxKind.ImplementsKeyword;
+    export function isFirstIdentifierOfNonEmittingHeritageClause(node: Node): boolean {
+        // Number of parents to climb from identifier is 2 for `implements I`, 3 for `implements x.I`
+        const heritageClause = tryCast(node.parent.parent, isHeritageClause) ?? tryCast(node.parent.parent?.parent, isHeritageClause);
+        return heritageClause?.token === SyntaxKind.ImplementsKeyword || heritageClause?.parent.kind === SyntaxKind.InterfaceDeclaration;
     }
 
     export function isExternalModuleImportEqualsDeclaration(node: Node): node is ImportEqualsDeclaration & { moduleReference: ExternalModuleReference } {
@@ -2765,13 +2766,20 @@ namespace ts {
             node.kind === SyntaxKind.PropertyAssignment && isAliasableExpression((node as PropertyAssignment).initializer);
     }
 
-    export function getTypeOnlyCompatibleAliasDeclarationFromName(node: Identifier): TypeOnlyCompatibleAliasDeclaration | undefined {
+    export function getAliasDeclarationFromName(node: EntityName): Declaration | undefined {
         switch (node.parent.kind) {
             case SyntaxKind.ImportClause:
             case SyntaxKind.ImportSpecifier:
             case SyntaxKind.NamespaceImport:
             case SyntaxKind.ExportSpecifier:
-                return node.parent as TypeOnlyCompatibleAliasDeclaration;
+            case SyntaxKind.ExportAssignment:
+            case SyntaxKind.ImportEqualsDeclaration:
+                return node.parent as Declaration;
+            case SyntaxKind.QualifiedName:
+                do {
+                    node = node.parent as QualifiedName;
+                } while (node.parent.kind === SyntaxKind.QualifiedName);
+                return getAliasDeclarationFromName(node);
         }
     }
 
@@ -6143,7 +6151,7 @@ namespace ts {
     export function isValidTypeOnlyAliasUseSite(useSite: Node): boolean {
         return !!(useSite.flags & NodeFlags.Ambient)
             || isPartOfTypeQuery(useSite)
-            || isFirstIdentifierOfImplementsClause(useSite)
+            || isFirstIdentifierOfNonEmittingHeritageClause(useSite)
             || isPartOfPossiblyValidTypeOrAbstractComputedPropertyName(useSite)
             || !isExpressionNode(useSite);
     }

src/testRunner/tsconfig.json

@@ -185,6 +185,7 @@
         "unittests/tsserver/textStorage.ts",
         "unittests/tsserver/telemetry.ts",
         "unittests/tsserver/typeAquisition.ts",
+        "unittests/tsserver/typeOnlyImportChains.ts",
         "unittests/tsserver/typeReferenceDirectives.ts",
         "unittests/tsserver/typingsInstaller.ts",
         "unittests/tsserver/untitledFiles.ts",