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]>
(cherry picked from commit 03597cf802a7a89c4853794e6206ab8ab003898d)

1 files changed, 5 insertions, 4 deletions

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index fac186a6379..d7e2f855ab9 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -2373,11 +2373,12 @@ 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) {