glsl2: Fail linking where the FS reads a varying that the VS doesn't write.

Fixes:
glsl1-varying read but not written
glsl1-varying var mismatch

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index ec3cc01d4046127909797275d43deeec1ebd1769..fa4fb493f227683f91c81e59438fad3e4cf349db 100644 (file)
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -1061,7 +1061,8 @@ assign_attribute_locations(gl_shader_program *prog, unsigned max_attribute_index
 
 
 void
-assign_varying_locations(gl_shader *producer, gl_shader *consumer)
+assign_varying_locations(struct gl_shader_program *prog,
+                        gl_shader *producer, gl_shader *consumer)
 {
    /* FINISHME: Set dynamically when geometry shader support is added. */
    unsigned output_index = VERT_RESULT_VAR0;
@@ -1128,11 +1129,32 @@ assign_varying_locations(gl_shader *producer, gl_shader *consumer)
       if ((var == NULL) || (var->mode != ir_var_in))
         continue;
 
-      /* An 'in' variable is only really a shader input if its value is written
-       * by the previous stage.
-       */
-      var->shader_in = (var->location != -1);
-      var->mode = ir_var_auto;
+      if (var->location == -1) {
+        if (prog->Version <= 120) {
+           /* On page 25 (page 31 of the PDF) of the GLSL 1.20 spec:
+            *
+            *     Only those varying variables used (i.e. read) in
+            *     the fragment shader executable must be written to
+            *     by the vertex shader executable; declaring
+            *     superfluous varying variables in a vertex shader is
+            *     permissible.
+            *
+            * We interpret this text as meaning that the VS must
+            * write the variable for the FS to read it.  See
+            * "glsl1-varying read but not written" in piglit.
+            */
+
+           linker_error_printf(prog, "fragment shader varying %s not written "
+                               "by vertex shader\n.", var->name);
+           prog->LinkStatus = false;
+        }
+
+        /* An 'in' variable is only really a shader input if its
+         * value is written by the previous stage.
+         */
+        var->shader_in = false;
+        var->mode = ir_var_auto;
+      }
    }
 }
 
@@ -1294,7 +1316,8 @@ link_shaders(struct gl_shader_program *prog)
         goto done;
 
    for (unsigned i = 1; i < prog->_NumLinkedShaders; i++)
-      assign_varying_locations(prog->_LinkedShaders[i - 1],
+      assign_varying_locations(prog,
+                              prog->_LinkedShaders[i - 1],
                               prog->_LinkedShaders[i]);
 
    /* FINISHME: Assign fragment shader output locations. */