Auto merge of #1321 - stouset:check-if-num-template-args-is-loaded, r=emilio

Check if `clang_Type_getNumTemplateArguments` is loaded before use

Fixes #1304, which reapplies #916 which was regressed by #915.

Author: bors-servo

src/clang.rs

@@ -911,6 +911,13 @@ impl Type {
     /// Get the number of template arguments this type has, or `None` if it is
     /// not some kind of template.
     pub fn num_template_args(&self) -> Option<u32> {
+        // If an old libclang is loaded, we have no hope of answering this
+        // question correctly. However, that's no reason to panic when
+        // generating bindings for simple C headers with an old libclang.
+        if !clang_Type_getNumTemplateArguments::is_loaded() {
+            return None
+        }
+
         let n = unsafe { clang_Type_getNumTemplateArguments(self.x) };
         if n >= 0 {
             Some(n as u32)
@@ -1639,8 +1646,11 @@ pub fn ast_dump(c: &Cursor, depth: isize) -> CXChildVisitResult {
             depth,
             format!(" {}spelling = \"{}\"", prefix, ty.spelling()),
         );
-        let num_template_args =
-            unsafe { clang_Type_getNumTemplateArguments(ty.x) };
+        let num_template_args = if clang_Type_getNumTemplateArguments::is_loaded() {
+            unsafe { clang_Type_getNumTemplateArguments(ty.x) }
+        } else {
+            -1
+        };
         if num_template_args >= 0 {
             print_indent(
                 depth,