Emit grammar error on quoted constructors and class fields named “constructor”

src/compiler/checker.ts

@@ -31468,6 +31468,9 @@ namespace ts {
                         return grammarErrorAtPos(node, node.end - 1, ";".length, Diagnostics._0_expected, "{");
                     }
                 }
+                else if (isClassLike(node.parent) && isStringLiteral(node.name) && node.name.text === "constructor" && (!compilerOptions.target || compilerOptions.target < ScriptTarget.ES5)) {
+                    return grammarErrorOnNode(node.name, Diagnostics.Quoted_constructors_have_previously_been_interpreted_as_methods_which_is_incorrect_In_TypeScript_3_6_they_will_be_correctly_parsed_as_constructors_In_the_meantime_consider_using_constructor_to_write_a_constructor_or_constructor_to_write_a_method);
+                }
                 if (checkGrammarForGenerator(node)) {
                     return true;
                 }

src/compiler/diagnosticMessages.json

@@ -2959,7 +2959,7 @@
         "category": "Error",
         "code": 4104
     },
-    
+
     "The current host does not support the '{0}' option.": {
         "category": "Error",
         "code": 5001
@@ -4954,5 +4954,9 @@
     "No value exists in scope for the shorthand property '{0}'. Either declare one or provide an initializer." :{
         "category": "Error",
         "code": 18004
+    },
+    "Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '[\"constructor\"]()' to write a method.": {
+        "category": "Error",
+        "code": 96000
     }
 }

tests/baselines/reference/quotedConstructors.errors.txt

@@ -0,0 +1,30 @@
+tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts(2,5): error TS96000: Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '["constructor"]()' to write a method.
+tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts(6,5): error TS96000: Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '["constructor"]()' to write a method.
+tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts(14,5): error TS96000: Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '["constructor"]()' to write a method.
+
+
+==== tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts (3 errors) ====
+    class C {
+        "constructor"() {} // Error in 3.5
+        ~~~~~~~~~~~~~
+!!! error TS96000: Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '["constructor"]()' to write a method.
+    }
+
+    class D {
+        'constructor'() {} // Error in 3.5
+        ~~~~~~~~~~~~~
+!!! error TS96000: Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '["constructor"]()' to write a method.
+    }
+
+    class E {
+        ['constructor']() {}
+    }
+
+    new class {
+        "constructor"() {} // Error in 3.5
+        ~~~~~~~~~~~~~
+!!! error TS96000: Quoted constructors have previously been interpreted as methods, which is incorrect. In TypeScript 3.6, they will be correctly parsed as constructors. In the meantime, consider using 'constructor()' to write a constructor, or '["constructor"]()' to write a method.
+    };
+
+    var o = { "constructor"() {} };
+

tests/baselines/reference/quotedConstructors.js

@@ -0,0 +1,46 @@
+//// [quotedConstructors.ts]
+class C {
+    "constructor"() {} // Error in 3.5
+}
+
+class D {
+    'constructor'() {} // Error in 3.5
+}
+
+class E {
+    ['constructor']() {}
+}
+
+new class {
+    "constructor"() {} // Error in 3.5
+};
+
+var o = { "constructor"() {} };
+
+
+//// [quotedConstructors.js]
+var C = /** @class */ (function () {
+    function C() {
+    }
+    C.prototype["constructor"] = function () { }; // Error in 3.5
+    return C;
+}());
+var D = /** @class */ (function () {
+    function D() {
+    }
+    D.prototype['constructor'] = function () { }; // Error in 3.5
+    return D;
+}());
+var E = /** @class */ (function () {
+    function E() {
+    }
+    E.prototype['constructor'] = function () { };
+    return E;
+}());
+new /** @class */ (function () {
+    function class_1() {
+    }
+    class_1.prototype["constructor"] = function () { }; // Error in 3.5
+    return class_1;
+}());
+var o = { "constructor": function () { } };

tests/baselines/reference/quotedConstructors.symbols

@@ -0,0 +1,33 @@
+=== tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts ===
+class C {
+>C : Symbol(C, Decl(quotedConstructors.ts, 0, 0))
+
+    "constructor"() {} // Error in 3.5
+>"constructor" : Symbol(C["constructor"], Decl(quotedConstructors.ts, 0, 9))
+}
+
+class D {
+>D : Symbol(D, Decl(quotedConstructors.ts, 2, 1))
+
+    'constructor'() {} // Error in 3.5
+>'constructor' : Symbol(D['constructor'], Decl(quotedConstructors.ts, 4, 9))
+}
+
+class E {
+>E : Symbol(E, Decl(quotedConstructors.ts, 6, 1))
+
+    ['constructor']() {}
+>['constructor'] : Symbol(E['constructor'], Decl(quotedConstructors.ts, 8, 9))
+>'constructor' : Symbol(E['constructor'], Decl(quotedConstructors.ts, 8, 9))
+}
+
+new class {
+    "constructor"() {} // Error in 3.5
+>"constructor" : Symbol((Anonymous class)["constructor"], Decl(quotedConstructors.ts, 12, 11))
+
+};
+
+var o = { "constructor"() {} };
+>o : Symbol(o, Decl(quotedConstructors.ts, 16, 3))
+>"constructor" : Symbol("constructor", Decl(quotedConstructors.ts, 16, 9))
+

tests/baselines/reference/quotedConstructors.types

@@ -0,0 +1,37 @@
+=== tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts ===
+class C {
+>C : C
+
+    "constructor"() {} // Error in 3.5
+>"constructor" : () => void
+}
+
+class D {
+>D : D
+
+    'constructor'() {} // Error in 3.5
+>'constructor' : () => void
+}
+
+class E {
+>E : E
+
+    ['constructor']() {}
+>['constructor'] : () => void
+>'constructor' : "constructor"
+}
+
+new class {
+>new class {    "constructor"() {} // Error in 3.5} : (Anonymous class)
+>class {    "constructor"() {} // Error in 3.5} : typeof (Anonymous class)
+
+    "constructor"() {} // Error in 3.5
+>"constructor" : () => void
+
+};
+
+var o = { "constructor"() {} };
+>o : { "constructor"(): void; }
+>{ "constructor"() {} } : { "constructor"(): void; }
+>"constructor" : () => void
+

tests/cases/conformance/classes/constructorDeclarations/quotedConstructors.ts

@@ -0,0 +1,17 @@
+class C {
+    "constructor"() {} // Error in 3.5
+}
+
+class D {
+    'constructor'() {} // Error in 3.5
+}
+
+class E {
+    ['constructor']() {}
+}
+
+new class {
+    "constructor"() {} // Error in 3.5
+};
+
+var o = { "constructor"() {} };