Fix type inferencing and syntax highlighting for unresolved type parameter in method return type

[eric-milles]

Consider the following:

class C {
  private <N extends Number> N m(Class<N> t) {
    t.newInstance()
  }
  void test() {
    def n = m()
  }
}

No class is supplied in the call "m()" and so no type witness exists for "N".

java.lang.AssertionError
	at org.eclipse.jdt.groovy.search.GenericsMapper.gatherGenerics(GenericsMapper.java:94)
	at org.eclipse.jdt.groovy.search.GenericsMapper.gatherGenerics(GenericsMapper.java:54)
	at org.eclipse.jdt.groovy.search.TypeLookupResult.resolveTypeParameterization(TypeLookupResult.java:268)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.lookupExpressionType(TypeInferencingVisitorWithRequestor.java:2759)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.handleSimpleExpression(TypeInferencingVisitorWithRequestor.java:2035)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.handleSimpleExpression(TypeInferencingVisitorWithRequestor.java:2040)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitConstantExpression(TypeInferencingVisitorWithRequestor.java:1004)
	at org.codehaus.groovy.ast.expr.ConstantExpression.visit(ConstantExpression.java:88)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitMethodCallExpression(TypeInferencingVisitorWithRequestor.java:1497)
	at org.codehaus.groovy.ast.expr.MethodCallExpression.visit(MethodCallExpression.java:78)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitBinaryExpression(TypeInferencingVisitorWithRequestor.java:782)
	at org.codehaus.groovy.ast.CodeVisitorSupport.visitDeclarationExpression(CodeVisitorSupport.java:335)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitDeclarationExpression(ClassCodeVisitorSupport.java:177)
	at org.codehaus.groovy.ast.expr.DeclarationExpression.visit(DeclarationExpression.java:89)
	at org.codehaus.groovy.ast.CodeVisitorSupport.visitExpressionStatement(CodeVisitorSupport.java:117)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitExpressionStatement(ClassCodeVisitorSupport.java:252)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitExpressionStatement(TypeInferencingVisitorWithRequestor.java:1141)
	at org.codehaus.groovy.ast.stmt.ExpressionStatement.visit(ExpressionStatement.java:41)
	at org.codehaus.groovy.ast.CodeVisitorSupport.visitBlockStatement(CodeVisitorSupport.java:86)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitBlockStatement(ClassCodeVisitorSupport.java:216)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitBlockStatement(TypeInferencingVisitorWithRequestor.java:870)
	at org.codehaus.groovy.ast.stmt.BlockStatement.visit(BlockStatement.java:70)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClassCodeContainer(ClassCodeVisitorSupport.java:165)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitConstructorOrMethod(TypeInferencingVisitorWithRequestor.java:1111)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitMethodInternal(TypeInferencingVisitorWithRequestor.java:658)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitJDT(TypeInferencingVisitorWithRequestor.java:466)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitJDT(TypeInferencingVisitorWithRequestor.java:375)
	at org.eclipse.jdt.groovy.search.TypeInferencingVisitorWithRequestor.visitCompilationUnit(TypeInferencingVisitorWithRequestor.java:255)
	at org.codehaus.groovy.eclipse.editor.highlighting.GatherSemanticReferences.findSemanticHighlightingReferences(GatherSemanticReferences.java:43)

[eric-milles]