Invariant declaration doesn't make a variable active

src/compiler/translator/CollectVariables.cpp

@@ -119,6 +119,7 @@ class CollectVariablesTraverser : public TIntermTraverser
                               GLenum shaderType,
                               const TExtensionBehavior &extensionBehavior);
 
+    bool visitInvariantDeclaration(Visit visit, TIntermInvariantDeclaration *node) override;
     void visitSymbol(TIntermSymbol *symbol) override;
     bool visitDeclaration(Visit, TIntermDeclaration *node) override;
     bool visitBinary(Visit visit, TIntermBinary *binaryNode) override;
@@ -336,11 +337,17 @@ InterfaceBlock *CollectVariablesTraverser::recordGLInUsed(const TType &glInType)
     }
 }
 
-// We want to check whether a uniform/varying is statically used
-// because we only count the used ones in packing computing.
-// Also, gl_FragCoord, gl_PointCoord, and gl_FrontFacing count
-// toward varying counting if they are statically used in a fragment
-// shader.
+bool CollectVariablesTraverser::visitInvariantDeclaration(Visit visit,
+                                                          TIntermInvariantDeclaration *node)
+{
+    // We should not mark variables as active just based on an invariant declaration, so we don't
+    // traverse the symbols declared invariant.
+    return false;
+}
+
+// We want to check whether a uniform/varying is active because we need to skip updating inactive
+// ones. We also only count the active ones in packing computing. Also, gl_FragCoord, gl_PointCoord,
+// and gl_FrontFacing count toward varying counting if they are active in a fragment shader.
 void CollectVariablesTraverser::visitSymbol(TIntermSymbol *symbol)
 {
     ASSERT(symbol != nullptr);

src/tests/compiler_tests/CollectVariables_test.cpp

@@ -2035,4 +2035,26 @@ TEST_F(CollectVertexVariablesTest, StaticallyUsedButNotActiveInstancedInterfaceB
     // See TODO in CollectVariables.cpp about tracking instanced interface block field static use.
     // EXPECT_TRUE(field.staticUse);
     EXPECT_FALSE(field.active);
-}
\ No newline at end of file
+}
+
+// Test a varying that is declared invariant but not otherwise used.
+TEST_F(CollectVertexVariablesTest, VaryingOnlyDeclaredInvariant)
+{
+    const std::string &shaderString =
+        R"(precision mediump float;
+        varying float vf;
+        invariant vf;
+        void main()
+        {
+        })";
+
+    compile(shaderString);
+
+    const auto &varyings = mTranslator->getOutputVaryings();
+    ASSERT_EQ(1u, varyings.size());
+
+    const Varying &varying = varyings[0];
+    EXPECT_EQ("vf", varying.name);
+    EXPECT_FALSE(varying.staticUse);
+    EXPECT_FALSE(varying.active);
+}