Improve error message for type parameter extending union

Author: JsonFreeman

src/compiler/checker.ts

@@ -4074,8 +4074,8 @@ module ts {
  }
  }
  else if (source.flags & TypeFlags.TypeParameter && sourceOrApparentType.flags & TypeFlags.Union) {
- if (result = isRelatedTo(sourceOrApparentType, <ObjectType>target, reportStructuralErrors)) {
-  errorInfo = saveErrorInfo;
+ errorInfo = saveErrorInfo;
+ if (result = isRelatedTo(sourceOrApparentType, target, reportErrors)) {
  return result;
  }
  }

tests/baselines/reference/typeParameterDiamond3.errors.txt

@@ -1,8 +1,8 @@
 tests/cases/compiler/typeParameterDiamond3.ts(8,13): error TS2322: Type 'T | U' is not assignable to type 'Top'.
  Type 'T' is not assignable to type 'Top'.
 tests/cases/compiler/typeParameterDiamond3.ts(9,13): error TS2322: Type 'Bottom' is not assignable to type 'T | U'.
- Type 'Bottom' is not assignable to type 'U'.
- Type 'Top | T | U' is not assignable to type 'U'.
+ Type 'Top | T | U' is not assignable to type 'T | U'.
+ Type 'Top' is not assignable to type 'T | U'.
  Type 'Top' is not assignable to type 'U'.
 tests/cases/compiler/typeParameterDiamond3.ts(10,13): error TS2322: Type 'Bottom' is not assignable to type 'Top'.
  Type 'Top | T | U' is not assignable to type 'Top'.
@@ -24,8 +24,8 @@ tests/cases/compiler/typeParameterDiamond3.ts(10,13): error TS2322: Type 'Bottom
  middle = bottom;
  ~~~~~~
 !!! error TS2322: Type 'Bottom' is not assignable to type 'T | U'.
-!!! error TS2322: Type 'Bottom' is not assignable to type 'U'.
-!!! error TS2322: Type 'Top | T | U' is not assignable to type 'U'.
+!!! error TS2322: Type 'Top | T | U' is not assignable to type 'T | U'.
+!!! error TS2322: Type 'Top' is not assignable to type 'T | U'.
 !!! error TS2322: Type 'Top' is not assignable to type 'U'.
  top = bottom;
  ~~~