fix53287 mergeSymbol checks if the resolved target can merge with t…

…he source (#58326)

src/compiler/checker.ts

@@ -2621,7 +2621,16 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (resolvedTarget === unknownSymbol) {
                     return source;
                 }
-                target = cloneSymbol(resolvedTarget);
+                if (
+                    !(resolvedTarget.flags & getExcludedSymbolFlags(source.flags)) ||
+                    (source.flags | resolvedTarget.flags) & SymbolFlags.Assignment
+                ) {
+                    target = cloneSymbol(resolvedTarget);
+                }
+                else {
+                    reportMergeSymbolError(target, source);
+                    return source;
+                }
             }
             // Javascript static-property-assignment declarations always merge, even though they are also values
             if (source.flags & SymbolFlags.ValueModule && target.flags & SymbolFlags.ValueModule && target.constEnumOnlyModule && !source.constEnumOnlyModule) {
@@ -2657,7 +2666,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 );
             }
         }
-        else { // error
+        else {
+            reportMergeSymbolError(target, source);
+        }
+        return target;
+
+        function reportMergeSymbolError(target: Symbol, source: Symbol) {
             const isEitherEnum = !!(target.flags & SymbolFlags.Enum || source.flags & SymbolFlags.Enum);
             const isEitherBlockScoped = !!(target.flags & SymbolFlags.BlockScopedVariable || source.flags & SymbolFlags.BlockScopedVariable);
             const message = isEitherEnum ? Diagnostics.Enum_declarations_can_only_merge_with_namespace_or_other_enum_declarations
@@ -2684,7 +2698,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (!isTargetPlainJs) addDuplicateDeclarationErrorsForSymbols(target, message, symbolName, source);
             }
         }
-        return target;
 
         function addDuplicateLocations(locs: Declaration[], symbol: Symbol): void {
             if (symbol.declarations) {

tests/baselines/reference/checkMergedGlobalUMDSymbol.errors.txt

@@ -1,21 +1,25 @@
-global.d.ts(6,16): error TS2403: Subsequent variable declarations must have the same type.  Variable 'THREE' must be of type 'typeof import("global")', but here has type 'typeof import("three")'.
+global.d.ts(3,21): error TS2451: Cannot redeclare block-scoped variable 'THREE'.
+global.d.ts(6,16): error TS2451: Cannot redeclare block-scoped variable 'THREE'.
 
 
 ==== three.d.ts (0 errors) ====
     export namespace THREE {
       export class Vector2 {}
     }
 
-==== global.d.ts (1 errors) ====
+==== global.d.ts (2 errors) ====
     import * as _three from './three';
 
     export as namespace THREE;
+                        ~~~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'THREE'.
+!!! related TS6203 global.d.ts:6:16: 'THREE' was also declared here.
 
     declare global {
       export const THREE: typeof _three;
                    ~~~~~
-!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'THREE' must be of type 'typeof import("global")', but here has type 'typeof import("three")'.
-!!! related TS6203 global.d.ts:1:1: 'THREE' was also declared here.
+!!! error TS2451: Cannot redeclare block-scoped variable 'THREE'.
+!!! related TS6203 global.d.ts:3:21: 'THREE' was also declared here.
     }
 
 ==== test.ts (0 errors) ====

tests/baselines/reference/checkMergedGlobalUMDSymbol.symbols

@@ -19,12 +19,12 @@ declare global {
 >global : Symbol(global, Decl(global.d.ts, 2, 26))
 
   export const THREE: typeof _three;
->THREE : Symbol(THREE, Decl(global.d.ts, 0, 0), Decl(global.d.ts, 5, 14))
+>THREE : Symbol(THREE, Decl(global.d.ts, 5, 14))
 >_three : Symbol(_three, Decl(global.d.ts, 0, 6))
 }
 
 === test.ts ===
 const m = THREE
 >m : Symbol(m, Decl(test.ts, 0, 5))
->THREE : Symbol(THREE, Decl(global.d.ts, 0, 0), Decl(global.d.ts, 5, 14))
+>THREE : Symbol(THREE, Decl(global.d.ts, 5, 14))
 

tests/baselines/reference/checkMergedGlobalUMDSymbol.types

@@ -24,16 +24,16 @@ declare global {
 >       : ^^^^^^^^^^^^^
 
   export const THREE: typeof _three;
->THREE : typeof import("global")
->      : ^^^^^^^^^^^^^^^^^^^^^^^
+>THREE : typeof _three
+>      : ^^^^^^^^^^^^^
 >_three : typeof _three
 >       : ^^^^^^^^^^^^^
 }
 
 === test.ts ===
 const m = THREE
->m : typeof import("global")
->  : ^^^^^^^^^^^^^^^^^^^^^^^
->THREE : typeof import("global")
->      : ^^^^^^^^^^^^^^^^^^^^^^^
+>m : typeof import("three")
+>  : ^^^^^^^^^^^^^^^^^^^^^^
+>THREE : typeof import("three")
+>      : ^^^^^^^^^^^^^^^^^^^^^^
 

tests/baselines/reference/checkerInitializationCrash.errors.txt

@@ -0,0 +1,47 @@
+/node_modules/@fullcalendar/core/index.d.ts(4,10): error TS2300: Duplicate identifier 'VNode'.
+/node_modules/@fullcalendar/react/index.d.ts(4,19): error TS2300: Duplicate identifier 'VNode'.
+
+
+==== /node_modules/@fullcalendar/react/index.d.ts (1 errors) ====
+    import * as react from 'react';
+    declare global {
+      namespace FullCalendarVDom {
+        export import VNode = react.ReactNode;
+                      ~~~~~
+!!! error TS2300: Duplicate identifier 'VNode'.
+!!! related TS6203 /node_modules/@fullcalendar/core/index.d.ts:4:10: 'VNode' was also declared here.
+      }
+    }
+
+    export default class FullCalendar {
+    }
+
+==== /node_modules/@fullcalendar/core/index.d.ts (1 errors) ====
+    import * as preact from 'preact';
+    declare global {
+      namespace FullCalendarVDom {
+        type VNode = preact.VNode<any>;
+             ~~~~~
+!!! error TS2300: Duplicate identifier 'VNode'.
+!!! related TS6203 /node_modules/@fullcalendar/react/index.d.ts:4:19: 'VNode' was also declared here.
+      }
+    }
+
+    export type EventInput = any;
+
+==== /node_modules/@types/react/index.d.ts (0 errors) ====
+    export = React;
+    export as namespace React;
+    declare namespace React {
+        type ReactNode = any;
+        function useMemo<T>(factory: () => T, deps: undefined): T;
+    }
+
+==== /node_modules/preact/index.d.ts (0 errors) ====
+    export as namespace preact;
+    export interface VNode<P = {}> {}
+
+==== /index.tsx (0 errors) ====
+    import FullCalendar from "@fullcalendar/react";
+    import { EventInput } from "@fullcalendar/core";
+

tests/baselines/reference/checkerInitializationCrash.symbols

@@ -13,7 +13,7 @@ declare global {
     export import VNode = react.ReactNode;
 >VNode : Symbol(FullCalendarVDom.VNode, Decl(index.d.ts, 2, 30))
 >react : Symbol(react, Decl(index.d.ts, 0, 6))
->ReactNode : Symbol(react.ReactNode, Decl(index.d.ts, 2, 25), Decl(index.d.ts, 2, 30))
+>ReactNode : Symbol(react.ReactNode, Decl(index.d.ts, 2, 25))
   }
 }
 
@@ -32,7 +32,7 @@ declare global {
 >FullCalendarVDom : Symbol(FullCalendarVDom, Decl(index.d.ts, 1, 16), Decl(index.d.ts, 1, 16))
 
     type VNode = preact.VNode<any>;
->VNode : Symbol(React.ReactNode, Decl(index.d.ts, 2, 25), Decl(index.d.ts, 2, 30))
+>VNode : Symbol(VNode, Decl(index.d.ts, 2, 30))
 >preact : Symbol(preact, Decl(index.d.ts, 0, 6))
 >VNode : Symbol(preact.VNode, Decl(index.d.ts, 0, 27))
   }
@@ -52,7 +52,7 @@ declare namespace React {
 >React : Symbol(React, Decl(index.d.ts, 1, 26))
 
     type ReactNode = any;
->ReactNode : Symbol(ReactNode, Decl(index.d.ts, 2, 25), Decl(index.d.ts, 2, 30))
+>ReactNode : Symbol(ReactNode, Decl(index.d.ts, 2, 25))
 
     function useMemo<T>(factory: () => T, deps: undefined): T;
 >useMemo : Symbol(useMemo, Decl(index.d.ts, 3, 25))

tests/baselines/reference/checkerInitializationCrash.types

@@ -39,14 +39,16 @@ declare global {
 
   namespace FullCalendarVDom {
     type VNode = preact.VNode<any>;
->VNode : any
+>VNode : VNode
+>      : ^^^^^
 >preact : any
 >       : ^^^
   }
 }
 
 export type EventInput = any;
 >EventInput : any
+>           : ^^^
 
 === /node_modules/@types/react/index.d.ts ===
 export = React;
@@ -63,6 +65,7 @@ declare namespace React {
 
     type ReactNode = any;
 >ReactNode : any
+>          : ^^^
 
     function useMemo<T>(factory: () => T, deps: undefined): T;
 >useMemo : <T>(factory: () => T, deps: undefined) => T

tests/baselines/reference/crashDeclareGlobalTypeofExport.errors.txt

@@ -0,0 +1,33 @@
+bar.d.ts(2,21): error TS2451: Cannot redeclare block-scoped variable 'foo'.
+bar.d.ts(6,11): error TS2451: Cannot redeclare block-scoped variable 'foo'.
+bar.d.ts(6,11): error TS2502: 'foo' is referenced directly or indirectly in its own type annotation.
+
+
+==== bar.d.ts (3 errors) ====
+    import * as foo from './foo'
+    export as namespace foo
+                        ~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'foo'.
+!!! related TS6203 bar.d.ts:6:11: 'foo' was also declared here.
+    export = foo;
+
+    declare global {
+        const foo: typeof foo;
+              ~~~
+!!! error TS2451: Cannot redeclare block-scoped variable 'foo'.
+!!! related TS6203 bar.d.ts:2:21: 'foo' was also declared here.
+              ~~~
+!!! error TS2502: 'foo' is referenced directly or indirectly in its own type annotation.
+    }
+
+==== foo.d.ts (0 errors) ====
+    interface Root {
+        /**
+         * A .default property for ES6 default import compatibility
+         */
+        default: Root;
+    }
+
+    declare const root: Root;
+    export = root;
+

tests/baselines/reference/crashDeclareGlobalTypeofExport.symbols

@@ -14,8 +14,8 @@ declare global {
 >global : Symbol(global, Decl(bar.d.ts, 2, 13))
 
     const foo: typeof foo;
->foo : Symbol(foo, Decl(foo.d.ts, 7, 13), Decl(bar.d.ts, 5, 9))
->foo : Symbol(foo, Decl(foo.d.ts, 7, 13), Decl(bar.d.ts, 5, 9))
+>foo : Symbol(foo, Decl(bar.d.ts, 5, 9))
+>foo : Symbol(foo, Decl(bar.d.ts, 5, 9))
 }
 
 === foo.d.ts ===

tests/baselines/reference/crashDeclareGlobalTypeofExport.types

@@ -18,10 +18,10 @@ declare global {
 >       : ^^^^^^^^^^^^^
 
     const foo: typeof foo;
->foo : Root
->    : ^^^^
->foo : Root
->    : ^^^^
+>foo : any
+>    : ^^^
+>foo : any
+>    : ^^^
 }
 
 === foo.d.ts ===

tests/baselines/reference/declarationFileNoCrashOnExtraExportModifier.errors.txt

@@ -1,8 +1,9 @@
 input.ts(1,1): error TS2309: An export assignment cannot be used in a module with other exported elements.
-input.ts(6,14): error TS2323: Cannot redeclare exported variable 'Sub'.
+input.ts(6,14): error TS2300: Duplicate identifier 'Sub'.
+input.ts(12,14): error TS2300: Duplicate identifier 'Sub'.
 
 
-==== input.ts (2 errors) ====
+==== input.ts (3 errors) ====
     export = exports;
     ~~~~~~~~~~~~~~~~~
 !!! error TS2309: An export assignment cannot be used in a module with other exported elements.
@@ -12,11 +13,15 @@ input.ts(6,14): error TS2323: Cannot redeclare exported variable 'Sub'.
     }
     export class Sub {
                  ~~~
-!!! error TS2323: Cannot redeclare exported variable 'Sub'.
+!!! error TS2300: Duplicate identifier 'Sub'.
+!!! related TS6203 input.ts:12:14: 'Sub' was also declared here.
         instance!: {
             t: number;
         };
     }
     declare namespace exports {
         export { Sub };
+                 ~~~
+!!! error TS2300: Duplicate identifier 'Sub'.
+!!! related TS6203 input.ts:6:14: 'Sub' was also declared here.
     }

tests/baselines/reference/declarationFileNoCrashOnExtraExportModifier.symbols

@@ -14,7 +14,7 @@ declare class exports {
 >t : Symbol(exports.t, Decl(input.ts, 2, 27))
 }
 export class Sub {
->Sub : Symbol(Sub, Decl(input.ts, 4, 1), Decl(input.ts, 4, 1))
+>Sub : Symbol(Sub, Decl(input.ts, 4, 1))
 
     instance!: {
 >instance : Symbol(Sub.instance, Decl(input.ts, 5, 18))

tests/baselines/reference/declarationFileNoCrashOnExtraExportModifier.types

@@ -36,6 +36,6 @@ declare namespace exports {
 >        : ^^^^^^^^^^^^^^
 
     export { Sub };
->Sub : typeof import("input").Sub
->    : ^^^^^^^^^^^^^^^^^^^^^^^^^^
+>Sub : typeof Sub
+>    : ^^^^^^^^^^
 }