Disallow type and interface declarations in statements with blockless bodies (#60183)

src/compiler/checker.ts

@@ -46774,6 +46774,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     function checkInterfaceDeclaration(node: InterfaceDeclaration) {
         // Grammar checking
         if (!checkGrammarModifiers(node)) checkGrammarInterfaceDeclaration(node);
+        if (!allowBlockDeclarations(node.parent)) {
+            grammarErrorOnNode(node, Diagnostics._0_declarations_can_only_be_declared_inside_a_block, "interface");
+        }
 
         checkTypeParameters(node.typeParameters);
         addLazyDiagnostic(() => {
@@ -46817,6 +46820,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // Grammar checking
         checkGrammarModifiers(node);
         checkTypeNameIsReserved(node.name, Diagnostics.Type_alias_name_cannot_be_0);
+        if (!allowBlockDeclarations(node.parent)) {
+            grammarErrorOnNode(node, Diagnostics._0_declarations_can_only_be_declared_inside_a_block, "type");
+        }
         checkExportsOnMergedDeclarations(node);
         checkTypeParameters(node.typeParameters);
         if (node.type.kind === SyntaxKind.IntrinsicKeyword) {
@@ -52051,7 +52057,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return false;
     }
 
-    function allowLetAndConstDeclarations(parent: Node): boolean {
+    function allowBlockDeclarations(parent: Node): boolean {
         switch (parent.kind) {
             case SyntaxKind.IfStatement:
             case SyntaxKind.DoStatement:
@@ -52062,14 +52068,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             case SyntaxKind.ForOfStatement:
                 return false;
             case SyntaxKind.LabeledStatement:
-                return allowLetAndConstDeclarations(parent.parent);
+                return allowBlockDeclarations(parent.parent);
         }
 
         return true;
     }
 
     function checkGrammarForDisallowedBlockScopedVariableStatement(node: VariableStatement) {
-        if (!allowLetAndConstDeclarations(node.parent)) {
+        if (!allowBlockDeclarations(node.parent)) {
             const blockScopeKind = getCombinedNodeFlagsCached(node.declarationList) & NodeFlags.BlockScoped;
             if (blockScopeKind) {
                 const keyword = blockScopeKind === NodeFlags.Let ? "let" :

tests/baselines/reference/typeAliasDeclarationEmit3.errors.txt

@@ -0,0 +1,30 @@
+typeAliasDeclarationEmit3.ts(3,14): error TS1156: 'type' declarations can only be declared inside a block.
+typeAliasDeclarationEmit3.ts(9,14): error TS1156: 'type' declarations can only be declared inside a block.
+typeAliasDeclarationEmit3.ts(15,14): error TS1156: 'type' declarations can only be declared inside a block.
+
+
+==== typeAliasDeclarationEmit3.ts (3 errors) ====
+    function f1(): void {
+        for (let i = 0; i < 1; i++)
+            type foo = [];
+                 ~~~
+!!! error TS1156: 'type' declarations can only be declared inside a block.
+            console.log('f1');
+    }
+    
+    function f2(): void {
+        while (true)
+            type foo = [];
+                 ~~~
+!!! error TS1156: 'type' declarations can only be declared inside a block.
+            console.log('f2');
+    }
+    
+    function f3(): void {
+        if (true)
+            type foo = [];
+                 ~~~
+!!! error TS1156: 'type' declarations can only be declared inside a block.
+            console.log('f3');
+    }
+    

tests/baselines/reference/typeInterfaceDeclarationsInBlockStatements1.errors.txt

@@ -0,0 +1,46 @@
+typeInterfaceDeclarationsInBlockStatements1.ts(4,18): error TS1156: 'type' declarations can only be declared inside a block.
+typeInterfaceDeclarationsInBlockStatements1.ts(12,21): error TS2304: Cannot find name 's'.
+typeInterfaceDeclarationsInBlockStatements1.ts(17,15): error TS1156: 'interface' declarations can only be declared inside a block.
+typeInterfaceDeclarationsInBlockStatements1.ts(29,21): error TS2304: Cannot find name 's'.
+
+
+==== typeInterfaceDeclarationsInBlockStatements1.ts (4 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/60175
+    
+    function f1() {
+      if (true) type s = string;
+                     ~
+!!! error TS1156: 'type' declarations can only be declared inside a block.
+      console.log("" as s);
+    }
+    
+    function f2() {
+      if (true) {
+        type s = string;
+      }
+      console.log("" as s);
+                        ~
+!!! error TS2304: Cannot find name 's'.
+    }
+    
+    function f3() {
+      if (true)
+        interface s {
+                  ~
+!!! error TS1156: 'interface' declarations can only be declared inside a block.
+          length: number;
+        }
+      console.log("" as s);
+    }
+    
+    function f4() {
+      if (true) {
+        interface s {
+          length: number;
+        }
+      }
+      console.log("" as s);
+                        ~
+!!! error TS2304: Cannot find name 's'.
+    }
+    

tests/baselines/reference/typeInterfaceDeclarationsInBlockStatements1.js

@@ -0,0 +1,65 @@
+//// [tests/cases/compiler/typeInterfaceDeclarationsInBlockStatements1.ts] ////
+
+//// [typeInterfaceDeclarationsInBlockStatements1.ts]
+// https://github.com/microsoft/TypeScript/issues/60175
+
+function f1() {
+  if (true) type s = string;
+  console.log("" as s);
+}
+
+function f2() {
+  if (true) {
+    type s = string;
+  }
+  console.log("" as s);
+}
+
+function f3() {
+  if (true)
+    interface s {
+      length: number;
+    }
+  console.log("" as s);
+}
+
+function f4() {
+  if (true) {
+    interface s {
+      length: number;
+    }
+  }
+  console.log("" as s);
+}
+
+
+//// [typeInterfaceDeclarationsInBlockStatements1.js]
+"use strict";
+// https://github.com/microsoft/TypeScript/issues/60175
+function f1() {
+    if (true)
+        ;
+    console.log("");
+}
+function f2() {
+    if (true) {
+    }
+    console.log("");
+}
+function f3() {
+    if (true)
+        ;
+    console.log("");
+}
+function f4() {
+    if (true) {
+    }
+    console.log("");
+}
+
+
+//// [typeInterfaceDeclarationsInBlockStatements1.d.ts]
+declare function f1(): void;
+declare function f2(): void;
+declare function f3(): void;
+declare function f4(): void;

tests/baselines/reference/typeInterfaceDeclarationsInBlockStatements1.symbols

@@ -0,0 +1,67 @@
+//// [tests/cases/compiler/typeInterfaceDeclarationsInBlockStatements1.ts] ////
+
+=== typeInterfaceDeclarationsInBlockStatements1.ts ===
+// https://github.com/microsoft/TypeScript/issues/60175
+
+function f1() {
+>f1 : Symbol(f1, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 0, 0))
+
+  if (true) type s = string;
+>s : Symbol(s, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 3, 11))
+
+  console.log("" as s);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>s : Symbol(s, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 3, 11))
+}
+
+function f2() {
+>f2 : Symbol(f2, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 5, 1))
+
+  if (true) {
+    type s = string;
+>s : Symbol(s, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 8, 13))
+  }
+  console.log("" as s);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>s : Symbol(s)
+}
+
+function f3() {
+>f3 : Symbol(f3, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 12, 1))
+
+  if (true)
+    interface s {
+>s : Symbol(s, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 15, 11))
+
+      length: number;
+>length : Symbol(s.length, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 16, 17))
+    }
+  console.log("" as s);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>s : Symbol(s, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 15, 11))
+}
+
+function f4() {
+>f4 : Symbol(f4, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 20, 1))
+
+  if (true) {
+    interface s {
+>s : Symbol(s, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 23, 13))
+
+      length: number;
+>length : Symbol(s.length, Decl(typeInterfaceDeclarationsInBlockStatements1.ts, 24, 17))
+    }
+  }
+  console.log("" as s);
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>s : Symbol(s)
+}
+

tests/baselines/reference/typeInterfaceDeclarationsInBlockStatements1.types

@@ -0,0 +1,114 @@
+//// [tests/cases/compiler/typeInterfaceDeclarationsInBlockStatements1.ts] ////
+
+=== typeInterfaceDeclarationsInBlockStatements1.ts ===
+// https://github.com/microsoft/TypeScript/issues/60175
+
+function f1() {
+>f1 : () => void
+>   : ^^^^^^^^^^
+
+  if (true) type s = string;
+>true : true
+>     : ^^^^
+>s : string
+>  : ^^^^^^
+
+  console.log("" as s);
+>console.log("" as s) : void
+>                     : ^^^^
+>console.log : (...data: any[]) => void
+>            : ^^^^    ^^     ^^^^^    
+>console : Console
+>        : ^^^^^^^
+>log : (...data: any[]) => void
+>    : ^^^^    ^^     ^^^^^    
+>"" as s : string
+>        : ^^^^^^
+>"" : ""
+>   : ^^
+}
+
+function f2() {
+>f2 : () => void
+>   : ^^^^^^^^^^
+
+  if (true) {
+>true : true
+>     : ^^^^
+
+    type s = string;
+>s : string
+>  : ^^^^^^
+  }
+  console.log("" as s);
+>console.log("" as s) : void
+>                     : ^^^^
+>console.log : (...data: any[]) => void
+>            : ^^^^    ^^     ^^^^^    
+>console : Console
+>        : ^^^^^^^
+>log : (...data: any[]) => void
+>    : ^^^^    ^^     ^^^^^    
+>"" as s : s
+>        : ^
+>"" : ""
+>   : ^^
+}
+
+function f3() {
+>f3 : () => void
+>   : ^^^^^^^^^^
+
+  if (true)
+>true : true
+>     : ^^^^
+
+    interface s {
+      length: number;
+>length : number
+>       : ^^^^^^
+    }
+  console.log("" as s);
+>console.log("" as s) : void
+>                     : ^^^^
+>console.log : (...data: any[]) => void
+>            : ^^^^    ^^     ^^^^^    
+>console : Console
+>        : ^^^^^^^
+>log : (...data: any[]) => void
+>    : ^^^^    ^^     ^^^^^    
+>"" as s : s
+>        : ^
+>"" : ""
+>   : ^^
+}
+
+function f4() {
+>f4 : () => void
+>   : ^^^^^^^^^^
+
+  if (true) {
+>true : true
+>     : ^^^^
+
+    interface s {
+      length: number;
+>length : number
+>       : ^^^^^^
+    }
+  }
+  console.log("" as s);
+>console.log("" as s) : void
+>                     : ^^^^
+>console.log : (...data: any[]) => void
+>            : ^^^^    ^^     ^^^^^    
+>console : Console
+>        : ^^^^^^^
+>log : (...data: any[]) => void
+>    : ^^^^    ^^     ^^^^^    
+>"" as s : s
+>        : ^
+>"" : ""
+>   : ^^
+}
+

tests/cases/compiler/typeInterfaceDeclarationsInBlockStatements1.ts

@@ -0,0 +1,33 @@
+// @strict: true
+// @declaration: true
+
+// https://github.com/microsoft/TypeScript/issues/60175
+
+function f1() {
+  if (true) type s = string;
+  console.log("" as s);
+}
+
+function f2() {
+  if (true) {
+    type s = string;
+  }
+  console.log("" as s);
+}
+
+function f3() {
+  if (true)
+    interface s {
+      length: number;
+    }
+  console.log("" as s);
+}
+
+function f4() {
+  if (true) {
+    interface s {
+      length: number;
+    }
+  }
+  console.log("" as s);
+}