Don’t create expando declarations on alias symbols

src/compiler/binder.ts

@@ -2980,6 +2980,9 @@ namespace ts {
         }
 
         function bindPotentiallyMissingNamespaces(namespaceSymbol: Symbol | undefined, entityName: BindableStaticNameExpression, isToplevel: boolean, isPrototypeProperty: boolean, containerIsClass: boolean) {
+            if (namespaceSymbol?.flags! & SymbolFlags.Alias) {
+                return namespaceSymbol;
+            }
             if (isToplevel && !isPrototypeProperty) {
                 // make symbols or add declarations for intermediate containers
                 const flags = SymbolFlags.Module | SymbolFlags.Assignment;

src/compiler/checker.ts

@@ -35217,39 +35217,36 @@ namespace ts {
             const target = resolveAlias(symbol);
 
             if (target !== unknownSymbol) {
-                const shouldSkipWithJSExpandoTargets = symbol.flags & SymbolFlags.Assignment;
-                if (!shouldSkipWithJSExpandoTargets) {
-                    // For external modules symbol represents local symbol for an alias.
-                    // This local symbol will merge any other local declarations (excluding other aliases)
-                    // and symbol.flags will contains combined representation for all merged declaration.
-                    // Based on symbol.flags we can compute a set of excluded meanings (meaning that resolved alias should not have,
-                    // otherwise it will conflict with some local declaration). Note that in addition to normal flags we include matching SymbolFlags.Export*
-                    // in order to prevent collisions with declarations that were exported from the current module (they still contribute to local names).
-                    symbol = getMergedSymbol(symbol.exportSymbol || symbol);
-                    const excludedMeanings =
-                        (symbol.flags & (SymbolFlags.Value | SymbolFlags.ExportValue) ? SymbolFlags.Value : 0) |
-                        (symbol.flags & SymbolFlags.Type ? SymbolFlags.Type : 0) |
-                        (symbol.flags & SymbolFlags.Namespace ? SymbolFlags.Namespace : 0);
-                    if (target.flags & excludedMeanings) {
-                        const message = node.kind === SyntaxKind.ExportSpecifier ?
-                            Diagnostics.Export_declaration_conflicts_with_exported_declaration_of_0 :
-                            Diagnostics.Import_declaration_conflicts_with_local_declaration_of_0;
-                        error(node, message, symbolToString(symbol));
-                    }
-
-                    // Don't allow to re-export something with no value side when `--isolatedModules` is set.
-                    if (compilerOptions.isolatedModules
-                        && node.kind === SyntaxKind.ExportSpecifier
-                        && !node.parent.parent.isTypeOnly
-                        && !(target.flags & SymbolFlags.Value)
-                        && !(node.flags & NodeFlags.Ambient)) {
-                        error(node, Diagnostics.Re_exporting_a_type_when_the_isolatedModules_flag_is_provided_requires_using_export_type);
-                    }
+                // For external modules, `symbol` represents the local symbol for an alias.
+                // This local symbol will merge any other local declarations (excluding other aliases)
+                // and symbol.flags will contains combined representation for all merged declaration.
+                // Based on symbol.flags we can compute a set of excluded meanings (meaning that resolved alias should not have,
+                // otherwise it will conflict with some local declaration). Note that in addition to normal flags we include matching SymbolFlags.Export*
+                // in order to prevent collisions with declarations that were exported from the current module (they still contribute to local names).
+                symbol = getMergedSymbol(symbol.exportSymbol || symbol);
+                const excludedMeanings =
+                    (symbol.flags & (SymbolFlags.Value | SymbolFlags.ExportValue) ? SymbolFlags.Value : 0) |
+                    (symbol.flags & SymbolFlags.Type ? SymbolFlags.Type : 0) |
+                    (symbol.flags & SymbolFlags.Namespace ? SymbolFlags.Namespace : 0);
+                if (target.flags & excludedMeanings) {
+                    const message = node.kind === SyntaxKind.ExportSpecifier ?
+                        Diagnostics.Export_declaration_conflicts_with_exported_declaration_of_0 :
+                        Diagnostics.Import_declaration_conflicts_with_local_declaration_of_0;
+                    error(node, message, symbolToString(symbol));
+                }
+
+                // Don't allow to re-export something with no value side when `--isolatedModules` is set.
+                if (compilerOptions.isolatedModules
+                    && node.kind === SyntaxKind.ExportSpecifier
+                    && !node.parent.parent.isTypeOnly
+                    && !(target.flags & SymbolFlags.Value)
+                    && !(node.flags & NodeFlags.Ambient)) {
+                    error(node, Diagnostics.Re_exporting_a_type_when_the_isolatedModules_flag_is_provided_requires_using_export_type);
                 }
 
                 if (isImportSpecifier(node) &&
                     (target.valueDeclaration && target.valueDeclaration.flags & NodeFlags.Deprecated
-                     || every(target.declarations, d => !!(d.flags & NodeFlags.Deprecated)))) {
+                        || every(target.declarations, d => !!(d.flags & NodeFlags.Deprecated)))) {
                     errorOrSuggestion(/* isError */ false, node.name, Diagnostics._0_is_deprecated, symbol.escapedName as string);
                 }
             }

tests/baselines/reference/expandoOnAlias.errors.txt

@@ -0,0 +1,25 @@
+tests/cases/conformance/salsa/test.js(4,5): error TS2339: Property 'config' does not exist on type 'typeof Vue'.
+
+
+==== tests/cases/conformance/salsa/vue.js (0 errors) ====
+    export class Vue {}
+    export const config = { x: 0 };
+
+==== tests/cases/conformance/salsa/test.js (1 errors) ====
+    import { Vue, config } from "./vue";
+
+    // Expando declarations aren't allowed on aliases.
+    Vue.config = {};
+        ~~~~~~
+!!! error TS2339: Property 'config' does not exist on type 'typeof Vue'.
+    new Vue();
+
+    // This is not an expando declaration; it's just a plain property assignment.
+    config.x = 1;
+
+    // This is not an expando declaration; it works because non-strict JS allows
+    // loosey goosey assignment on objects.
+    config.y = {};
+    config.x;
+    config.y;
+

tests/baselines/reference/expandoOnAlias.js

@@ -0,0 +1,33 @@
+//// [tests/cases/conformance/salsa/expandoOnAlias.ts] ////
+
+//// [vue.js]
+export class Vue {}
+export const config = { x: 0 };
+
+//// [test.js]
+import { Vue, config } from "./vue";
+
+// Expando declarations aren't allowed on aliases.
+Vue.config = {};
+new Vue();
+
+// This is not an expando declaration; it's just a plain property assignment.
+config.x = 1;
+
+// This is not an expando declaration; it works because non-strict JS allows
+// loosey goosey assignment on objects.
+config.y = {};
+config.x;
+config.y;
+
+
+
+
+//// [vue.d.ts]
+export class Vue {
+}
+export namespace config {
+    const x: number;
+}
+//// [test.d.ts]
+export {};

tests/baselines/reference/expandoOnAlias.symbols

@@ -0,0 +1,39 @@
+=== tests/cases/conformance/salsa/vue.js ===
+export class Vue {}
+>Vue : Symbol(Vue, Decl(vue.js, 0, 0))
+
+export const config = { x: 0 };
+>config : Symbol(config, Decl(vue.js, 1, 12))
+>x : Symbol(x, Decl(vue.js, 1, 23))
+
+=== tests/cases/conformance/salsa/test.js ===
+import { Vue, config } from "./vue";
+>Vue : Symbol(Vue, Decl(test.js, 0, 8))
+>config : Symbol(config, Decl(test.js, 0, 13))
+
+// Expando declarations aren't allowed on aliases.
+Vue.config = {};
+>Vue : Symbol(Vue, Decl(test.js, 0, 8))
+
+new Vue();
+>Vue : Symbol(Vue, Decl(test.js, 0, 8))
+
+// This is not an expando declaration; it's just a plain property assignment.
+config.x = 1;
+>config.x : Symbol(x, Decl(vue.js, 1, 23))
+>config : Symbol(config, Decl(test.js, 0, 13))
+>x : Symbol(x, Decl(vue.js, 1, 23))
+
+// This is not an expando declaration; it works because non-strict JS allows
+// loosey goosey assignment on objects.
+config.y = {};
+>config : Symbol(config, Decl(test.js, 0, 13))
+
+config.x;
+>config.x : Symbol(x, Decl(vue.js, 1, 23))
+>config : Symbol(config, Decl(test.js, 0, 13))
+>x : Symbol(x, Decl(vue.js, 1, 23))
+
+config.y;
+>config : Symbol(config, Decl(test.js, 0, 13))
+

tests/baselines/reference/expandoOnAlias.types

@@ -0,0 +1,54 @@
+=== tests/cases/conformance/salsa/vue.js ===
+export class Vue {}
+>Vue : Vue
+
+export const config = { x: 0 };
+>config : { x: number; }
+>{ x: 0 } : { x: number; }
+>x : number
+>0 : 0
+
+=== tests/cases/conformance/salsa/test.js ===
+import { Vue, config } from "./vue";
+>Vue : typeof Vue
+>config : { x: number; }
+
+// Expando declarations aren't allowed on aliases.
+Vue.config = {};
+>Vue.config = {} : {}
+>Vue.config : any
+>Vue : typeof Vue
+>config : any
+>{} : {}
+
+new Vue();
+>new Vue() : Vue
+>Vue : typeof Vue
+
+// This is not an expando declaration; it's just a plain property assignment.
+config.x = 1;
+>config.x = 1 : 1
+>config.x : number
+>config : { x: number; }
+>x : number
+>1 : 1
+
+// This is not an expando declaration; it works because non-strict JS allows
+// loosey goosey assignment on objects.
+config.y = {};
+>config.y = {} : {}
+>config.y : any
+>config : { x: number; }
+>y : any
+>{} : {}
+
+config.x;
+>config.x : number
+>config : { x: number; }
+>x : number
+
+config.y;
+>config.y : any
+>config : { x: number; }
+>y : any
+

tests/baselines/reference/exportDefaultMarksIdentifierAsUsed.symbols

@@ -7,10 +7,8 @@ export default Obj;
 
 === tests/cases/compiler/b.js ===
 import Obj from './a';
->Obj : Symbol(Obj, Decl(b.js, 0, 6), Decl(b.js, 0, 22))
+>Obj : Symbol(Obj, Decl(b.js, 0, 6))
 
 Obj.fn = function() {};
->Obj.fn : Symbol(Obj.fn, Decl(b.js, 0, 22))
->Obj : Symbol(Obj, Decl(b.js, 0, 6), Decl(b.js, 0, 22))
->fn : Symbol(Obj.fn, Decl(b.js, 0, 22))
+>Obj : Symbol(Obj, Decl(b.js, 0, 6))
 

tests/baselines/reference/exportDefaultMarksIdentifierAsUsed.types

@@ -8,12 +8,12 @@ export default Obj;
 
 === tests/cases/compiler/b.js ===
 import Obj from './a';
->Obj : typeof Obj
+>Obj : {}
 
 Obj.fn = function() {};
 >Obj.fn = function() {} : () => void
->Obj.fn : () => void
->Obj : typeof Obj
->fn : () => void
+>Obj.fn : error
+>Obj : {}
+>fn : any
 >function() {} : () => void
 

tests/baselines/reference/propertyAssignmentOnImportedSymbol.symbols

@@ -4,10 +4,8 @@ export var hurk = {}
 
 === tests/cases/conformance/salsa/bug24658.js ===
 import { hurk } from './mod1'
->hurk : Symbol(hurk, Decl(bug24658.js, 0, 8), Decl(bug24658.js, 0, 29))
+>hurk : Symbol(hurk, Decl(bug24658.js, 0, 8))
 
 hurk.expando = 4
->hurk.expando : Symbol(hurk.expando, Decl(bug24658.js, 0, 29))
->hurk : Symbol(hurk, Decl(bug24658.js, 0, 8), Decl(bug24658.js, 0, 29))
->expando : Symbol(hurk.expando, Decl(bug24658.js, 0, 29))
+>hurk : Symbol(hurk, Decl(bug24658.js, 0, 8))
 

tests/baselines/reference/propertyAssignmentOnImportedSymbol.types

@@ -5,12 +5,12 @@ export var hurk = {}
 
 === tests/cases/conformance/salsa/bug24658.js ===
 import { hurk } from './mod1'
->hurk : typeof hurk
+>hurk : {}
 
 hurk.expando = 4
 >hurk.expando = 4 : 4
->hurk.expando : number
->hurk : typeof hurk
->expando : number
+>hurk.expando : any
+>hurk : {}
+>expando : any
 >4 : 4
 

tests/cases/conformance/salsa/expandoOnAlias.ts

@@ -0,0 +1,24 @@
+// @allowJs: true
+// @checkJs: true
+// @declaration: true
+// @emitDeclarationOnly: true
+
+// @Filename: vue.js
+export class Vue {}
+export const config = { x: 0 };
+
+// @Filename: test.js
+import { Vue, config } from "./vue";
+
+// Expando declarations aren't allowed on aliases.
+Vue.config = {};
+new Vue();
+
+// This is not an expando declaration; it's just a plain property assignment.
+config.x = 1;
+
+// This is not an expando declaration; it works because non-strict JS allows
+// loosey goosey assignment on objects.
+config.y = {};
+config.x;
+config.y;