microsoft · DanielRosenwasser · Aug 23, 2017 · Aug 18, 2017 · Aug 18, 2017 · Aug 18, 2017
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -9077,11 +9077,26 @@ namespace ts {
                                 else {
                                     // use the property's value declaration if the property is assigned inside the literal itself
                                     const objectLiteralDeclaration = source.symbol && firstOrUndefined(source.symbol.declarations);
+                                    let suggestion;
                                     if (prop.valueDeclaration && findAncestor(prop.valueDeclaration, d => d === objectLiteralDeclaration)) {
-                                        errorNode = prop.valueDeclaration;
+                                        const propDeclaration = prop.valueDeclaration as ObjectLiteralElementLike;
+                                        Debug.assertNode(propDeclaration, isObjectLiteralElementLike);
+
+                                        errorNode = propDeclaration;
+
+                                        if (isIdentifier(propDeclaration.name)) {
+                                            suggestion = getSuggestionForNonexistentProperty(propDeclaration.name, target);
+                                        }
+                                    }
+
+                                    if (suggestion !== undefined) {
+                                        reportError(Diagnostics.Object_literal_may_only_specify_known_properties_but_0_does_not_exist_in_type_1_Did_you_mean_to_write_2,
+                                            symbolToString(prop), typeToString(target), unescapeLeadingUnderscores(suggestion));
+                                    }
+                                    else {
+                                        reportError(Diagnostics.Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1,
+                                            symbolToString(prop), typeToString(target));
                                     }
-                                    reportError(Diagnostics.Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1,
-                                        symbolToString(prop), typeToString(target));
                                 }
                             }
                             return true;
@@ -14686,8 +14701,8 @@ namespace ts {
                 }
             }
             const suggestion = getSuggestionForNonexistentProperty(propNode, containingType);
-            if (suggestion) {
-                errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1_Did_you_mean_2, declarationNameToString(propNode), typeToString(containingType), suggestion);
+            if (suggestion !== undefined) {
+                errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1_Did_you_mean_2, declarationNameToString(propNode), typeToString(containingType), unescapeLeadingUnderscores(suggestion));
             }
             else {
                 errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1, declarationNameToString(propNode), typeToString(containingType));

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
@@ -1359,7 +1359,7 @@ namespace ts {
         };
     }
 
-    export function chainDiagnosticMessages(details: DiagnosticMessageChain, message: DiagnosticMessage, ...args: any[]): DiagnosticMessageChain;
+    export function chainDiagnosticMessages(details: DiagnosticMessageChain, message: DiagnosticMessage, ...args: string[]): DiagnosticMessageChain;
     export function chainDiagnosticMessages(details: DiagnosticMessageChain, message: DiagnosticMessage): DiagnosticMessageChain {
         let text = getLocaleSpecificMessage(message);
 

diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
@@ -1912,10 +1912,14 @@
         "category": "Error",
         "code": 2560
     },
-    "Base class expressions cannot reference class type parameters.": {
+    "Object literal may only specify known properties, but '{0}' does not exist in type '{1}'. Did you mean to write '{2}'?": {
         "category": "Error",
         "code": 2561
     },
+    "Base class expressions cannot reference class type parameters.": {
+        "category": "Error",
+        "code": 2562
+    },
     "JSX element attributes type '{0}' may not be a union type.": {
         "category": "Error",
         "code": 2600

diff --git a/tests/baselines/reference/baseExpressionTypeParameters.errors.txt b/tests/baselines/reference/baseExpressionTypeParameters.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/compiler/baseExpressionTypeParameters.ts(10,27): error TS2561: Base class expressions cannot reference class type parameters.
+tests/cases/compiler/baseExpressionTypeParameters.ts(10,27): error TS2562: Base class expressions cannot reference class type parameters.
 
 
 ==== tests/cases/compiler/baseExpressionTypeParameters.ts (1 errors) ====
@@ -13,7 +13,7 @@ tests/cases/compiler/baseExpressionTypeParameters.ts(10,27): error TS2561: Base
 
     class Gen<T> extends base<T>() {}  // Error, T not in scope
                               ~
-!!! error TS2561: Base class expressions cannot reference class type parameters.
+!!! error TS2562: Base class expressions cannot reference class type parameters.
     class Spec extends Gen<string> {}
 
     <string>Spec.prop;
diff --git a/tests/baselines/reference/nestedFreshLiteral.errors.txt b/tests/baselines/reference/nestedFreshLiteral.errors.txt
@@ -4,7 +4,7 @@ tests/cases/compiler/nestedFreshLiteral.ts(12,21): error TS2322: Type '{ nested:
       Type '{ prop: { colour: string; }; }' is not assignable to type 'NestedSelector'.
         Types of property 'prop' are incompatible.
           Type '{ colour: string; }' is not assignable to type 'CSSProps'.
-            Object literal may only specify known properties, and 'colour' does not exist in type 'CSSProps'.
+            Object literal may only specify known properties, but 'colour' does not exist in type 'CSSProps'. Did you mean to write 'color'?
 
 
 ==== tests/cases/compiler/nestedFreshLiteral.ts (1 errors) ====
@@ -27,5 +27,5 @@ tests/cases/compiler/nestedFreshLiteral.ts(12,21): error TS2322: Type '{ nested:
 !!! error TS2322:       Type '{ prop: { colour: string; }; }' is not assignable to type 'NestedSelector'.
 !!! error TS2322:         Types of property 'prop' are incompatible.
 !!! error TS2322:           Type '{ colour: string; }' is not assignable to type 'CSSProps'.
-!!! error TS2322:             Object literal may only specify known properties, and 'colour' does not exist in type 'CSSProps'.
+!!! error TS2322:             Object literal may only specify known properties, but 'colour' does not exist in type 'CSSProps'. Did you mean to write 'color'?
     }
diff --git a/tests/baselines/reference/objectLiteralExcessProperties.errors.txt b/tests/baselines/reference/objectLiteralExcessProperties.errors.txt
@@ -1,5 +1,5 @@
 tests/cases/compiler/objectLiteralExcessProperties.ts(9,18): error TS2322: Type '{ forword: string; }' is not assignable to type 'Book'.
-  Object literal may only specify known properties, and 'forword' does not exist in type 'Book'.
+  Object literal may only specify known properties, but 'forword' does not exist in type 'Book'. Did you mean to write 'foreword'?
 tests/cases/compiler/objectLiteralExcessProperties.ts(11,27): error TS2322: Type '{ foreward: string; }' is not assignable to type 'string | Book'.
   Object literal may only specify known properties, and 'foreward' does not exist in type 'string | Book'.
 tests/cases/compiler/objectLiteralExcessProperties.ts(13,53): error TS2322: Type '({ foreword: string; } | { forwards: string; })[]' is not assignable to type 'Book | Book[]'.
@@ -8,9 +8,9 @@ tests/cases/compiler/objectLiteralExcessProperties.ts(13,53): error TS2322: Type
       Type '{ forwards: string; }' is not assignable to type 'Book'.
         Object literal may only specify known properties, and 'forwards' does not exist in type 'Book'.
 tests/cases/compiler/objectLiteralExcessProperties.ts(15,42): error TS2322: Type '{ foreword: string; colour: string; }' is not assignable to type 'Book & Cover'.
-  Object literal may only specify known properties, and 'colour' does not exist in type 'Book & Cover'.
+  Object literal may only specify known properties, but 'colour' does not exist in type 'Book & Cover'. Did you mean to write 'color'?
 tests/cases/compiler/objectLiteralExcessProperties.ts(17,26): error TS2322: Type '{ foreward: string; color: string; }' is not assignable to type 'Book & Cover'.
-  Object literal may only specify known properties, and 'foreward' does not exist in type 'Book & Cover'.
+  Object literal may only specify known properties, but 'foreward' does not exist in type 'Book & Cover'. Did you mean to write 'foreword'?
 tests/cases/compiler/objectLiteralExcessProperties.ts(19,57): error TS2322: Type '{ foreword: string; color: string; price: number; }' is not assignable to type 'Book & Cover'.
   Object literal may only specify known properties, and 'price' does not exist in type 'Book & Cover'.
 tests/cases/compiler/objectLiteralExcessProperties.ts(21,43): error TS2322: Type '{ foreword: string; price: number; }' is not assignable to type 'Book & number'.
@@ -22,7 +22,7 @@ tests/cases/compiler/objectLiteralExcessProperties.ts(25,27): error TS2322: Type
 tests/cases/compiler/objectLiteralExcessProperties.ts(33,27): error TS2322: Type '{ 0: { colour: string; }; }' is not assignable to type 'Indexed'.
   Property '0' is incompatible with index signature.
     Type '{ colour: string; }' is not assignable to type 'Cover'.
-      Object literal may only specify known properties, and 'colour' does not exist in type 'Cover'.
+      Object literal may only specify known properties, but 'colour' does not exist in type 'Cover'. Did you mean to write 'color'?
 
 
 ==== tests/cases/compiler/objectLiteralExcessProperties.ts (10 errors) ====
@@ -37,7 +37,7 @@ tests/cases/compiler/objectLiteralExcessProperties.ts(33,27): error TS2322: Type
     var b1: Book = { forword: "oops" };
                      ~~~~~~~~~~~~~~~
 !!! error TS2322: Type '{ forword: string; }' is not assignable to type 'Book'.
-!!! error TS2322:   Object literal may only specify known properties, and 'forword' does not exist in type 'Book'.
+!!! error TS2322:   Object literal may only specify known properties, but 'forword' does not exist in type 'Book'. Did you mean to write 'foreword'?
 
     var b2: Book | string = { foreward: "nope" };
                               ~~~~~~~~~~~~~~~~
@@ -55,12 +55,12 @@ tests/cases/compiler/objectLiteralExcessProperties.ts(33,27): error TS2322: Type
     var b4: Book & Cover = { foreword: "hi", colour: "blue" };
                                              ~~~~~~~~~~~~~~
 !!! error TS2322: Type '{ foreword: string; colour: string; }' is not assignable to type 'Book & Cover'.
-!!! error TS2322:   Object literal may only specify known properties, and 'colour' does not exist in type 'Book & Cover'.
+!!! error TS2322:   Object literal may only specify known properties, but 'colour' does not exist in type 'Book & Cover'. Did you mean to write 'color'?
 
     var b5: Book & Cover = { foreward: "hi", color: "blue" };
                              ~~~~~~~~~~~~~~
 !!! error TS2322: Type '{ foreward: string; color: string; }' is not assignable to type 'Book & Cover'.
-!!! error TS2322:   Object literal may only specify known properties, and 'foreward' does not exist in type 'Book & Cover'.
+!!! error TS2322:   Object literal may only specify known properties, but 'foreward' does not exist in type 'Book & Cover'. Did you mean to write 'foreword'?
 
     var b6: Book & Cover = { foreword: "hi", color: "blue", price: 10.99 };
                                                             ~~~~~~~~~~~~
@@ -93,5 +93,5 @@ tests/cases/compiler/objectLiteralExcessProperties.ts(33,27): error TS2322: Type
 !!! error TS2322: Type '{ 0: { colour: string; }; }' is not assignable to type 'Indexed'.
 !!! error TS2322:   Property '0' is incompatible with index signature.
 !!! error TS2322:     Type '{ colour: string; }' is not assignable to type 'Cover'.
-!!! error TS2322:       Object literal may only specify known properties, and 'colour' does not exist in type 'Cover'.
+!!! error TS2322:       Object literal may only specify known properties, but 'colour' does not exist in type 'Cover'. Did you mean to write 'color'?
 
diff --git a/tests/baselines/reference/spellingSuggestionLeadingUnderscores01.errors.txt b/tests/baselines/reference/spellingSuggestionLeadingUnderscores01.errors.txt
@@ -0,0 +1,28 @@
+tests/cases/compiler/spellingSuggestionLeadingUnderscores01.ts(6,3): error TS2551: Property '___foo' does not exist on type '{ __foo: 10; }'. Did you mean '__foo'?
+tests/cases/compiler/spellingSuggestionLeadingUnderscores01.ts(14,5): error TS2322: Type '{ ___foo: number; }' is not assignable to type '{ __foo: number; }'.
+  Object literal may only specify known properties, but '___foo' does not exist in type '{ __foo: number; }'. Did you mean to write '__foo'?
+
+
+==== tests/cases/compiler/spellingSuggestionLeadingUnderscores01.ts (2 errors) ====
+    // @filename abc.ts
+    export declare let a: {
+        __foo: 10,
+    }
+
+    a.___foo
+      ~~~~~~
+!!! error TS2551: Property '___foo' does not exist on type '{ __foo: 10; }'. Did you mean '__foo'?
+
+    // @filename def.ts
+    export let b: {
+        __foo: number
+    }
+
+    b = {
+        ___foo: 100,
+        ~~~~~~~~~~~
+!!! error TS2322: Type '{ ___foo: number; }' is not assignable to type '{ __foo: number; }'.
+!!! error TS2322:   Object literal may only specify known properties, but '___foo' does not exist in type '{ __foo: number; }'. Did you mean to write '__foo'?
+    }
+
+
diff --git a/tests/baselines/reference/spellingSuggestionLeadingUnderscores01.js b/tests/baselines/reference/spellingSuggestionLeadingUnderscores01.js
@@ -0,0 +1,26 @@
+//// [spellingSuggestionLeadingUnderscores01.ts]
+// @filename abc.ts
+export declare let a: {
+    __foo: 10,
+}
+
+a.___foo
+
+// @filename def.ts
+export let b: {
+    __foo: number
+}
+
+b = {
+    ___foo: 100,
+}
+
+
+
+//// [spellingSuggestionLeadingUnderscores01.js]
+"use strict";
+exports.__esModule = true;
+exports.a.___foo;
+exports.b = {
+    ___foo: 100
+};
diff --git a/tests/cases/compiler/spellingSuggestionLeadingUnderscores01.ts b/tests/cases/compiler/spellingSuggestionLeadingUnderscores01.ts
@@ -0,0 +1,17 @@
+// @module: commonjs
+// @filename abc.ts
+export declare let a: {
+    __foo: 10,
+}
+
+a.___foo
+
+// @filename def.ts
+export let b: {
+    __foo: number
+}
+
+b = {
+    ___foo: 100,
+}
+