Don't try to swizzle void.

Test/baseResults/invalidSwizzle.vert.out

+invalidSwizzle.vert
+ERROR: 0:6: 'xx' : does not apply to this type:  global void
+ERROR: 0:7: 'xy' : does not apply to this type:  global void
+ERROR: 2 compilation errors.  No code generated.
+
+
+Shader version: 420
+ERROR: node is still EOpNull!
+0:5  Function Definition: main( ( global void)
+0:5    Function Parameters: 
+0:6    Sequence
+0:6      Function Call: f( ( global void)
+0:7      Function Call: f( ( global void)
+0:?   Linker Objects
+0:?     'gl_VertexID' ( gl_VertexId int VertexId)
+0:?     'gl_InstanceID' ( gl_InstanceId int InstanceId)
+
+
+Linked vertex stage:
+
+ERROR: Linking vertex stage: No function definition (body) found: 
+    f(
+
+Shader version: 420
+ERROR: node is still EOpNull!
+0:5  Function Definition: main( ( global void)
+0:5    Function Parameters: 
+0:6    Sequence
+0:6      Function Call: f( ( global void)
+0:7      Function Call: f( ( global void)
+0:?   Linker Objects
+0:?     'gl_VertexID' ( gl_VertexId int VertexId)
+0:?     'gl_InstanceID' ( gl_InstanceId int InstanceId)
+

Test/invalidSwizzle.vert

+#version 420
+
+void f();
+
+void main() {
+    f().xx; // Scalar swizzle does not apply to void
+    f().xy; // Vector swizzle does not apply either
+}
\ No newline at end of file

glslang/MachineIndependent/ParseHelper.cpp

@@ -663,7 +663,7 @@ TIntermTyped* TParseContext::handleDotDereference(const TSourceLoc& loc, TInterm
     // leaving swizzles and struct/block dereferences.
 
     TIntermTyped* result = base;
-    if (base->isVector() || base->isScalar()) {
+    if (base->getBasicType() != EbtVoid && (base->isVector() || base->isScalar())) {
         if (base->isScalar()) {
             const char* dotFeature = "scalar swizzle";
             requireProfile(loc, ~EEsProfile, dotFeature);

gtests/AST.FromFile.cpp

@@ -188,6 +188,7 @@ INSTANTIATE_TEST_CASE_P(
         "structDeref.frag",
         "structure.frag",
         "swizzle.frag",
+        "invalidSwizzle.vert",
         "syntaxError.frag",
         "test.frag",
         "texture.frag",