Sema: make source location in checkCallConvSupportsVarArgs more meaningful

As calling convention may not be specified explicitly in the source,
so use va_arg's location instead.

Signed-off-by: Tw <tw19881113@gmail.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/Sema.zig b/src/Sema.zig
index 16765d1a89..c513962d89 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -9669,7 +9669,13 @@ fn funcCommon(
         if (is_generic) {
             return sema.fail(block, func_src, "generic function cannot be variadic", .{});
         }
-        try sema.checkCallConvSupportsVarArgs(block, cc_src, cc);
+        const va_args_src = block.src(.{
+            .fn_proto_param = .{
+                .fn_proto_node_offset = src_node_offset,
+                .param_index = @intCast(block.params.len), // va_arg must be the last parameter
+            },
+        });
+        try sema.checkCallConvSupportsVarArgs(block, va_args_src, cc);
     }
 
     const ret_poison = bare_return_type.isGenericPoison();