glsl: Fix condition to generate shader link error

GL_ARB_ES2_compatibility doesn't say anything about shader linking
when one of the shaders (vertex or fragment shader) is absent. So,
the extension shouldn't change the behavior specified in GLSL
specification.

Tested the behavior on proprietary linux drivers of NVIDIA and AMD.
Both of them allow linking a version 100 shader program in OpenGL
context, when one of the shaders is absent.

Makes following Khronos CTS tests to pass:
successfulcompilevert_linkprogram.test
successfulcompilefrag_linkprogram.test

Cc: [email protected]
Signed-off-by: Anuj Phogat <[email protected]>
Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 5 insertions, 4 deletions

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 72a3860f36b..7d605d7e59b 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -2441,11 +2441,12 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
       goto done;
 
    /* OpenGL ES requires that a vertex shader and a fragment shader both be
-    * present in a linked program.  By checking prog->IsES, we also
-    * catch the GL_ARB_ES2_compatibility case.
+    * present in a linked program. GL_ARB_ES2_compatibility doesn't say
+    * anything about shader linking when one of the shaders (vertex or
+    * fragment shader) is absent. So, the extension shouldn't change the
+    * behavior specified in GLSL specification.
     */
-   if (!prog->InternalSeparateShader &&
-       (ctx->API == API_OPENGLES2 || prog->IsES)) {
+   if (!prog->InternalSeparateShader && ctx->API == API_OPENGLES2) {
       if (prog->_LinkedShaders[MESA_SHADER_VERTEX] == NULL) {
 	 linker_error(prog, "program lacks a vertex shader\n");
       } else if (prog->_LinkedShaders[MESA_SHADER_FRAGMENT] == NULL) {