improve error message for using property of type as type

src/compiler/checker.ts

@@ -3148,6 +3148,30 @@ namespace ts {
             return symbol.parent ? getFullyQualifiedName(symbol.parent, containingLocation) + "." + symbolToString(symbol) : symbolToString(symbol, containingLocation, /*meaning*/ undefined, SymbolFormatFlags.DoNotIncludeSymbolChain | SymbolFormatFlags.AllowAnyNodeKind);
         }
 
+        function getFullQualifiedName(node: QualifiedName) {
+            while(isQualifiedName(node.parent)) {
+                node = node.parent;
+            }
+            return node;
+        }
+
+        function tryGetQualifiedNameAsValue(node: QualifiedName) {
+            let left: Identifier | QualifiedName = getFirstIdentifier(node);
+            let symbol = resolveName(left, left.escapedText, SymbolFlags.Value, undefined, left, /*isUse*/ true);
+            if (!symbol) {
+                return undefined;
+            }
+            while (isQualifiedName(left.parent)) {
+                const type = getTypeOfSymbol(symbol);
+                symbol = getPropertyOfType(type, left.parent.right.escapedText);
+                if (!symbol) {
+                    return undefined;
+                }
+                left = left.parent;
+            }
+            return symbol;
+        }
+
         /**
          * Resolves a qualified name and any involved aliases.
          */
@@ -3199,9 +3223,14 @@ namespace ts {
                         const declarationName = declarationNameToString(right);
                         const suggestionForNonexistentModule = getSuggestedSymbolForNonexistentModule(right, namespace);
                         const exportedTypeSymbol = getMergedSymbol(getSymbol(getExportsOfSymbol(namespace), right.escapedText, SymbolFlags.Type));
+                        const fullQualifiedName = isQualifiedName(name) && getFullQualifiedName(name);
+                        const canSuggestTypeof = fullQualifiedName && !isTypeOfExpression(fullQualifiedName.parent) && tryGetQualifiedNameAsValue(fullQualifiedName);
                         if (suggestionForNonexistentModule) {
                             error(right, Diagnostics._0_has_no_exported_member_named_1_Did_you_mean_2, namespaceName, declarationName, symbolToString(suggestionForNonexistentModule));
                         }
+                        else if (canSuggestTypeof) {
+                            error(name, Diagnostics._0_refers_to_a_value_but_is_being_used_as_a_type_here_Did_you_mean_typeof_0, entityNameToString(fullQualifiedName as QualifiedName));
+                        }
                         else if (meaning & SymbolFlags.Namespace && exportedTypeSymbol && isQualifiedName(name.parent)) {
                             error(name.parent.right, Diagnostics.Cannot_access_0_1_because_0_is_a_type_but_not_a_namespace_Did_you_mean_to_retrieve_the_type_of_the_property_1_in_0_with_0_1, symbolToString(exportedTypeSymbol), unescapeLeadingUnderscores(name.parent.right.escapedText));
                         }

tests/baselines/reference/errorForUsingPropertyOfTypeAsType03.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/compiler/errorForUsingPropertyOfTypeAsType03.ts(11,23): error TS2713: Cannot access 'Red.toString' because 'Red' is a type, but not a namespace. Did you mean to retrieve the type of the property 'toString' in 'Red' with 'Red["toString"]'?
+tests/cases/compiler/errorForUsingPropertyOfTypeAsType03.ts(11,13): error TS2749: 'Color.Red.toString' refers to a value, but is being used as a type here. Did you mean 'typeof Color.Red.toString'?
 tests/cases/compiler/errorForUsingPropertyOfTypeAsType03.ts(13,19): error TS2339: Property 'Red' does not exist on type 'Color'.
 tests/cases/compiler/errorForUsingPropertyOfTypeAsType03.ts(19,13): error TS2702: 'C1' only refers to a type, but is being used as a namespace here.
 tests/cases/compiler/errorForUsingPropertyOfTypeAsType03.ts(20,13): error TS2702: 'C1' only refers to a type, but is being used as a namespace here.
@@ -19,8 +19,8 @@ tests/cases/compiler/errorForUsingPropertyOfTypeAsType03.ts(24,13): error TS2713
         type C2 = typeof Color;
 
         let a1: Color.Red.toString;
-                          ~~~~~~~~
-!!! error TS2713: Cannot access 'Red.toString' because 'Red' is a type, but not a namespace. Did you mean to retrieve the type of the property 'toString' in 'Red' with 'Red["toString"]'?
+                ~~~~~~~~~
+!!! error TS2749: 'Color.Red.toString' refers to a value, but is being used as a type here. Did you mean 'typeof Color.Red.toString'?
         let a2: Color.Red["toString"];
         let a3: Color["Red"]["toString"];
                       ~~~~~

tests/baselines/reference/genericFunduleInModule.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/compiler/genericFunduleInModule.ts(8,10): error TS2694: Namespace 'A' has no exported member 'B'.
+tests/cases/compiler/genericFunduleInModule.ts(8,8): error TS2749: 'A.B' refers to a value, but is being used as a type here. Did you mean 'typeof A.B'?
 
 
 ==== tests/cases/compiler/genericFunduleInModule.ts (1 errors) ====
@@ -10,6 +10,6 @@ tests/cases/compiler/genericFunduleInModule.ts(8,10): error TS2694: Namespace 'A
     }
 
     var b: A.B;
-             ~
-!!! error TS2694: Namespace 'A' has no exported member 'B'.
+           ~~~
+!!! error TS2749: 'A.B' refers to a value, but is being used as a type here. Did you mean 'typeof A.B'?
     A.B(1);

tests/baselines/reference/genericFunduleInModule2.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/compiler/genericFunduleInModule2.ts(11,10): error TS2694: Namespace 'A' has no exported member 'B'.
+tests/cases/compiler/genericFunduleInModule2.ts(11,8): error TS2749: 'A.B' refers to a value, but is being used as a type here. Did you mean 'typeof A.B'?
 
 
 ==== tests/cases/compiler/genericFunduleInModule2.ts (1 errors) ====
@@ -13,6 +13,6 @@ tests/cases/compiler/genericFunduleInModule2.ts(11,10): error TS2694: Namespace
     }
 
     var b: A.B;
-             ~
-!!! error TS2694: Namespace 'A' has no exported member 'B'.
+           ~~~
+!!! error TS2749: 'A.B' refers to a value, but is being used as a type here. Did you mean 'typeof A.B'?
     A.B(1);

tests/baselines/reference/importClause_namespaceImport.errors.txt

@@ -1,6 +1,6 @@
 /b.ts(2,1): error TS1361: 'types' cannot be used as a value because it was imported using 'import type'.
 /b.ts(3,1): error TS1361: 'types' cannot be used as a value because it was imported using 'import type'.
-/b.ts(4,14): error TS2694: Namespace '"/a"' has no exported member 'Value'.
+/b.ts(4,8): error TS2749: 'types.Value' refers to a value, but is being used as a type here. Did you mean 'typeof types.Value'?
 /b.ts(5,7): error TS2741: Property 'a' is missing in type '{}' but required in type 'A'.
 /b.ts(6,7): error TS2741: Property 'b' is missing in type '{}' but required in type 'B'.
 /b.ts(8,13): error TS1361: 'types' cannot be used as a value because it was imported using 'import type'.
@@ -23,8 +23,8 @@
 !!! error TS1361: 'types' cannot be used as a value because it was imported using 'import type'.
 !!! related TS1376 /b.ts:1:18: 'types' was imported here.
     let v: types.Value;
-                 ~~~~~
-!!! error TS2694: Namespace '"/a"' has no exported member 'Value'.
+           ~~~~~~~~~~~
+!!! error TS2749: 'types.Value' refers to a value, but is being used as a type here. Did you mean 'typeof types.Value'?
     const a: types.A = {};
           ~
 !!! error TS2741: Property 'a' is missing in type '{}' but required in type 'A'.

tests/baselines/reference/parserharness.errors.txt

@@ -2,7 +2,7 @@ tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(16,21): er
 tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(17,21): error TS6053: File 'tests/cases/conformance/parser/ecmascript5/compiler/typescript.ts' not found.
 tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(18,21): error TS6053: File 'tests/cases/conformance/parser/ecmascript5/services/typescriptServices.ts' not found.
 tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(19,21): error TS6053: File 'tests/cases/conformance/parser/ecmascript5/RealWorld/diff.ts' not found.
-tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(21,29): error TS2694: Namespace 'Harness' has no exported member 'Assert'.
+tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(21,21): error TS2749: 'Harness.Assert' refers to a value, but is being used as a type here. Did you mean 'typeof Harness.Assert'?
 tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(25,17): error TS2304: Cannot find name 'IIO'.
 tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(41,12): error TS2304: Cannot find name 'ActiveXObject'.
 tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(43,19): error TS2580: Cannot find name 'require'. Do you need to install type definitions for node? Try `npm i --save-dev @types/node`.
@@ -140,8 +140,8 @@ tests/cases/conformance/parser/ecmascript5/RealWorld/parserharness.ts(2030,32):
 !!! error TS6053: File 'tests/cases/conformance/parser/ecmascript5/RealWorld/diff.ts' not found.
 
     declare var assert: Harness.Assert;
-                                ~~~~~~
-!!! error TS2694: Namespace 'Harness' has no exported member 'Assert'.
+                        ~~~~~~~~~~~~~~
+!!! error TS2749: 'Harness.Assert' refers to a value, but is being used as a type here. Did you mean 'typeof Harness.Assert'?
     declare var it;
     declare var describe;
     declare var run;