Add check for builtin.cap() parameter.

Fixes #2235.

Author: sjamesr

src/com/goide/highlighting/GoAnnotator.java

@@ -112,6 +112,34 @@ else if (element instanceof GoBuiltinCallExpr) {
         checkMakeCall(call, holder);
       }
     }
+    else if (element instanceof GoCallExpr) {
+      GoCallExpr call = (GoCallExpr)element;
+      if (call.getExpression() instanceof GoReferenceExpression) {
+        GoReferenceExpression reference = (GoReferenceExpression)call.getExpression();
+        if ("cap".equals(reference.getText())) {
+          if (GoPsiImplUtil.builtin(reference.getReference().resolve())) {
+            checkCapCall(call, holder);
+          }
+        }
+      }
+    }
+  }
+
+  private static void checkCapCall(@NotNull GoCallExpr capCall, @NotNull AnnotationHolder holder) {
+    if (capCall.getArgumentList().getExpressionList().size() != 1) {
+      return;
+    }
+    GoType exprType = capCall.getArgumentList().getExpressionList().get(0).getGoType(null);
+    if (exprType == null) {
+      return;
+    }
+    GoType baseType = getBaseType(exprType);
+    if (baseType instanceof GoPointerType) {
+      baseType = ((GoPointerType)baseType).getType();
+    }
+    if (!(baseType instanceof GoArrayOrSliceType || baseType instanceof GoChannelType)) {
+      holder.createErrorAnnotation(capCall.getArgumentList().getExpressionList().get(0), "Invalid argument for cap");
+    }
   }
 
   private static void checkMakeCall(@NotNull GoBuiltinCallExpr call, @NotNull AnnotationHolder holder) {

testData/highlighting/builtinFuncCalls.go

@@ -53,4 +53,21 @@ func main() {
 	foo(make(chan func(), <error descr="Non-integer size argument to make">true</error>))
 	foo(make(chan func(), <error descr="Non-integer size argument to make">complex(17,4)</error>))
 	foo(make(chan func(), <error descr="Non-integer size argument to make">"1"</error>))
+
+	type someChan chan int
+	type capChan someChan
+
+	var capTest1 e
+	var capTest2 a
+	var capTest3 capChan
+	var capTest4 int
+	foo(cap<error descr="not enough arguments in call to cap">()</error>)
+	foo(cap<error descr="too many arguments in call to cap">(capTest1, capTest2)</error>)
+	foo(cap(capTest1))
+	foo(cap(<error descr="Invalid argument for cap">capTest2</error>))
+	foo(cap(capTest3))
+	foo(cap(<error descr="Invalid argument for cap">capTest4</error>))
+	foo(cap(<error descr="Invalid argument for cap">map[string]struct{}{}</error>))
+	foo(cap(&[4]string{"a", "b", "c", "d"}))
+	foo(cap([]string{}))
 }