Make bodiless declarations an error in JS (#54439)

src/compiler/diagnosticMessages.json

@@ -6556,6 +6556,10 @@
         "category": "Error",
         "code": 8016
     },
+    "Signature declarations can only be used in TypeScript files.": {
+        "category": "Error",
+        "code": 8017
+    },
     "Report errors in .js files.": {
         "category": "Message",
         "code": 8019

src/compiler/program.ts

@@ -3022,6 +3022,14 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
                     case SyntaxKind.TypeAliasDeclaration:
                         diagnostics.push(createDiagnosticForNode(node, Diagnostics.Type_aliases_can_only_be_used_in_TypeScript_files));
                         return "skip";
+                    case SyntaxKind.Constructor:
+                    case SyntaxKind.MethodDeclaration:
+                    case SyntaxKind.FunctionDeclaration:
+                        if (!(node as FunctionLikeDeclaration).body) {
+                            diagnostics.push(createDiagnosticForNode(node, Diagnostics.Signature_declarations_can_only_be_used_in_TypeScript_files));
+                            return "skip";
+                        }
+                        return;
                     case SyntaxKind.EnumDeclaration:
                         const enumKeyword = Debug.checkDefined(tokenToString(SyntaxKind.EnumKeyword));
                         diagnostics.push(createDiagnosticForNode(node, Diagnostics._0_declarations_can_only_be_used_in_TypeScript_files, enumKeyword));

tests/baselines/reference/jsFileCompilationConstructorOverloadSyntax.errors.txt

@@ -0,0 +1,10 @@
+a.js(2,3): error TS8017: Signature declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    class A {
+      constructor();
+      ~~~~~~~~~~~~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    }
+    

tests/baselines/reference/jsFileCompilationConstructorOverloadSyntax.symbols

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/jsFileCompilationConstructorOverloadSyntax.ts] ////
+
+=== a.js ===
+class A {
+>A : Symbol(A, Decl(a.js, 0, 0))
+
+  constructor();
+}
+

tests/baselines/reference/jsFileCompilationConstructorOverloadSyntax.types

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/jsFileCompilationConstructorOverloadSyntax.ts] ////
+
+=== a.js ===
+class A {
+>A : A
+
+  constructor();
+}
+

tests/baselines/reference/jsFileCompilationFunctionOverloadSyntax.errors.txt

@@ -0,0 +1,8 @@
+a.js(1,10): error TS8017: Signature declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    function foo();
+             ~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    

tests/baselines/reference/jsFileCompilationFunctionOverloadSyntax.symbols

@@ -0,0 +1,6 @@
+//// [tests/cases/compiler/jsFileCompilationFunctionOverloadSyntax.ts] ////
+
+=== a.js ===
+function foo();
+>foo : Symbol(foo, Decl(a.js, 0, 0))
+

tests/baselines/reference/jsFileCompilationFunctionOverloadSyntax.types

@@ -0,0 +1,6 @@
+//// [tests/cases/compiler/jsFileCompilationFunctionOverloadSyntax.ts] ////
+
+=== a.js ===
+function foo();
+>foo : () => any
+

tests/baselines/reference/jsFileCompilationMethodOverloadSyntax.errors.txt

@@ -0,0 +1,10 @@
+a.js(2,3): error TS8017: Signature declarations can only be used in TypeScript files.
+
+
+==== a.js (1 errors) ====
+    class A {
+      foo();
+      ~~~
+!!! error TS8017: Signature declarations can only be used in TypeScript files.
+    }
+    

tests/baselines/reference/jsFileCompilationMethodOverloadSyntax.symbols

@@ -0,0 +1,10 @@
+//// [tests/cases/compiler/jsFileCompilationMethodOverloadSyntax.ts] ////
+
+=== a.js ===
+class A {
+>A : Symbol(A, Decl(a.js, 0, 0))
+
+  foo();
+>foo : Symbol(A.foo, Decl(a.js, 0, 9))
+}
+

tests/baselines/reference/jsFileCompilationMethodOverloadSyntax.types

@@ -0,0 +1,10 @@
+//// [tests/cases/compiler/jsFileCompilationMethodOverloadSyntax.ts] ////
+
+=== a.js ===
+class A {
+>A : A
+
+  foo();
+>foo : () => any
+}
+

tests/cases/compiler/jsFileCompilationConstructorOverloadSyntax.ts

@@ -0,0 +1,6 @@
+// @allowJs: true
+// @noEmit: true
+// @filename: a.js
+class A {
+  constructor();
+}

tests/cases/compiler/jsFileCompilationFunctionOverloadSyntax.ts

@@ -0,0 +1,4 @@
+// @allowJs: true
+// @noEmit: true
+// @filename: a.js
+function foo();

tests/cases/compiler/jsFileCompilationMethodOverloadSyntax.ts

@@ -0,0 +1,6 @@
+// @allowJs: true
+// @noEmit: true
+// @filename: a.js
+class A {
+  foo();
+}