glsl: Improve error message when read-only vars are written

Improves the cases when:
* an explicit assignment references the read-only variable
* an 'out' or 'inout' function parameter references the read-only variable

1 files changed, 21 insertions, 6 deletions

diff --git a/src/glsl/ast_function.cpp b/src/glsl/ast_function.cpp
index 6ecf779c935..3e5e345389a 100644
--- a/src/glsl/ast_function.cpp
+++ b/src/glsl/ast_function.cpp
@@ -145,12 +145,27 @@ match_function_by_name(exec_list *instructions, const char *name,
 
 	 if ((formal->mode == ir_var_out)
 	     || (formal->mode == ir_var_inout)) {
-	    if (! actual->is_lvalue()) {
-	       /* FINISHME: Log a better diagnostic here.  There is no way
-		* FINISHME: to tell the user which parameter is invalid.
-		*/
-	       _mesa_glsl_error(loc, state, "`%s' parameter is not lvalue",
-				(formal->mode == ir_var_out) ? "out" : "inout");
+	    const char *mode = NULL;
+	    switch (formal->mode) {
+	    case ir_var_out:   mode = "out";   break;
+	    case ir_var_inout: mode = "inout"; break;
+	    default:           assert(false);  break;
+	    }
+            /* FIXME: 'loc' is incorrect (as of 2011-01-21). It is always
+             * FIXME: 0:0(0).
+             */
+	    if (actual->variable_referenced()
+	        && actual->variable_referenced()->read_only) {
+	       _mesa_glsl_error(loc, state,
+	                        "function parameter '%s %s' references the "
+	                        "read-only variable '%s'",
+	                        mode, formal->name,
+	                        actual->variable_referenced()->name);
+
+	    } else if (!actual->is_lvalue()) {
+               _mesa_glsl_error(loc, state,
+                                "function parameter '%s %s' is not an lvalue",
+                                mode, formal->name);
 	    }
 	 }