Proper disabling of extensions related to GLSL layout qualifier.

So the disabling can be detected.

src/Magnum/Extensions.h

@@ -101,7 +101,7 @@ namespace GL {
         _extension(GL,ARB,texture_query_lod,            GL210, GL400) // #73
         _extension(GL,ARB,texture_compression_bptc,     GL310, GL420) // #77
         _extension(GL,ARB,blend_func_extended,          GL210, GL330) // #78
-        _extension(GL,ARB,explicit_attrib_location, /*!*/ GL320, GL330) // #79
+        _extension(GL,ARB,explicit_attrib_location,     GL210, GL330) // #79
         _extension(GL,ARB,occlusion_query2,             GL210, GL330) // #80
         _extension(GL,ARB,sampler_objects,              GL210, GL330) // #81
         _extension(GL,ARB,shader_bit_encoding,    /*?*/ GL210, GL330) // #82
@@ -125,7 +125,7 @@ namespace GL {
         _extension(GL,ARB,viewport_array,               GL210, GL410) // #100
         _extension(GL,ARB,robustness,                   GL210,  None) // #105
         _extension(GL,ARB,base_instance,                GL210, GL420) // #107
-        _extension(GL,ARB,shading_language_420pack, /*!*/ GL320, GL420) // #108
+        _extension(GL,ARB,shading_language_420pack,     GL300, GL420) // #108
         _extension(GL,ARB,transform_feedback_instanced, GL210, GL420) // #109
         _extension(GL,ARB,compressed_texture_pixel_storage, GL210, GL420) // #110
         _extension(GL,ARB,conservative_depth,           GL300, GL420) // #111
@@ -142,7 +142,7 @@ namespace GL {
         _extension(GL,ARB,texture_view,                 GL210, GL430) // #124
         _extension(GL,ARB,vertex_attrib_binding,        GL210, GL430) // #125
         _extension(GL,ARB,ES3_compatibility,            GL330, GL430) // #127
-        _extension(GL,ARB,explicit_uniform_location, /*!*/ GL320, GL430) // #128
+        _extension(GL,ARB,explicit_uniform_location,    GL210, GL430) // #128
         _extension(GL,ARB,fragment_layer_viewport,      GL300, GL430) // #129
         _extension(GL,ARB,framebuffer_no_attachments,   GL210, GL430) // #130
         _extension(GL,ARB,internalformat_query2,        GL210, GL430) // #131
@@ -296,21 +296,6 @@ namespace GL {
 #undef _extension
 #endif
 
-/*
-    Notes (marked with ! above)
-
-    ARB_explicit_attrib_location, ARB_explicit_uniform_location don't work
-    with GLSL 1.20 (compiler error related to layout qualifier on Mesa), 1.30
-    (compiler error related to layout qualifier on NVidia) or 1.40 (compiler
-    error on Mac OS X), bumping minimal required version to GL 3.2 even if both
-    have *2.1* as minimal.
-
-    ARB_shading_language_420pack (particularly sampler bindings) doesn't work
-    with GLSL 1.40 (compiler error related to layout qualifier, similar to the
-    above), bumping minimal required version to GL 3.2 even that it has *3.0*
-    as minimal.
-*/
-
 }
 
 }

src/Magnum/Implementation/setupDriverWorkarounds.cpp

@@ -33,6 +33,15 @@ void Context::setupDriverWorkarounds() {
         if(_extensionRequiredVersion[Extensions::extension::Index] < Version::version) \
             _extensionRequiredVersion[Extensions::extension::Index] = Version::version
 
+    #ifndef MAGNUM_TARGET_GLES
+    /* Layout qualifier causes compiler error with GLSL 1.20 on Mesa, GLSL 1.30
+       on NVidia and 1.40 on Mac OS X */
+    /** @todo Different version on different vendors? */
+    _setRequiredVersion(GL::ARB::explicit_attrib_location, GL320);
+    _setRequiredVersion(GL::ARB::explicit_uniform_location, GL320);
+    _setRequiredVersion(GL::ARB::shading_language_420pack, GL320);
+    #endif
+
     #ifdef MAGNUM_TARGET_GLES
     /* Disable extensions for which we need extension loader, as they would
        crash otherwise. */

src/Magnum/Test/ContextGLTest.cpp

@@ -73,10 +73,17 @@ void ContextGLTest::isExtensionSupported() {
     if(!Context::current()->isExtensionSupported<Extensions::GL::EXT::texture_filter_anisotropic>())
         CORRADE_SKIP(Extensions::GL::EXT::texture_filter_anisotropic::string() + std::string(" extension should be supported, can't test"));
 
+    if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_attrib_location>())
+        CORRADE_SKIP(Extensions::GL::ARB::explicit_attrib_location::string() + std::string(" extension should be supported, can't test"));
+
     /* Test that we have proper extension list parser */
     std::string extensions(reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS)));
     CORRADE_VERIFY(extensions.find(Extensions::GL::EXT::texture_filter_anisotropic::string()) != std::string::npos);
     CORRADE_VERIFY(extensions.find(Extensions::GL::GREMEDY::string_marker::string()) == std::string::npos);
+
+    /* This is disabled in GL < 3.2 to work around GLSL compiler bugs */
+    CORRADE_VERIFY(!Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_attrib_location>(Version::GL310));
+    CORRADE_VERIFY(Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_attrib_location>(Version::GL320));
     #else
     CORRADE_SKIP("No useful extensions to test on OpenGL ES");
     #endif
@@ -87,8 +94,15 @@ void ContextGLTest::isExtensionDisabled() {
     if(!Context::current()->isExtensionSupported<Extensions::GL::APPLE::vertex_array_object>())
         CORRADE_SKIP(Extensions::GL::APPLE::vertex_array_object::string() + std::string(" extension should be supported, can't test"));
 
+    if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_attrib_location>())
+        CORRADE_SKIP(Extensions::GL::ARB::explicit_attrib_location::string() + std::string(" extension should be supported, can't test"));
+
     /* This is not disabled anywhere */
     CORRADE_VERIFY(!Context::current()->isExtensionDisabled<Extensions::GL::APPLE::vertex_array_object>());
+
+    /* This is disabled in GL < 3.2 to work around GLSL compiler bugs */
+    CORRADE_VERIFY(Context::current()->isExtensionDisabled<Extensions::GL::ARB::explicit_attrib_location>(Version::GL310));
+    CORRADE_VERIFY(!Context::current()->isExtensionDisabled<Extensions::GL::ARB::explicit_attrib_location>(Version::GL320));
     #else
     CORRADE_SKIP("No useful extensions to test on OpenGL ES");
     #endif