Auto merge of #224 - fitzgen:type-is-valid, r=emilio

Add `clang::Type::is_valid` and use it instead of checking self.kind() against CXType_Invalid

Needed `is_valid()` when debugging, so figured we should land this and update places where we compare against the magical sentinel value.

r? @emilio

Author: bors-servo

src/clang.rs

@@ -639,7 +639,7 @@ impl Type {
                 let ret = Type {
                     x: unsafe { clang_getPointeeType(self.x) },
                 };
-                debug_assert!(ret.kind() != CXType_Invalid);
+                debug_assert!(ret.is_valid());
                 Some(ret)
             }
             _ => None,
@@ -652,7 +652,7 @@ impl Type {
         let current_type = Type {
             x: unsafe { clang_getElementType(self.x) },
         };
-        if current_type.kind() != CXType_Invalid {
+        if current_type.is_valid() {
             Some(current_type)
         } else {
             None
@@ -691,10 +691,10 @@ impl Type {
         let rt = Type {
             x: unsafe { clang_getResultType(self.x) },
         };
-        if rt.kind() == CXType_Invalid {
-            None
-        } else {
+        if rt.is_valid() {
             Some(rt)
+        } else {
+            None
         }
     }
 
@@ -714,6 +714,11 @@ impl Type {
             }
         }
     }
+
+    /// Is this a valid type?
+    pub fn is_valid(&self) -> bool {
+        self.kind() != CXType_Invalid
+    }
 }
 
 /// An iterator for a type's template arguments.