Fixup single element swizzle type determination.

For a swizzle with one element (eg vec.x) the result type is just the
type of the vector, instead of a new vector.

Change-Id: I04ddb22da61db1c3553d465e4e5f9d6b32beae83
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/20062
Reviewed-by: David Neto <dneto@google.com>
diff --git a/src/type_determiner.cc b/src/type_determiner.cc
index d0dd7ff..b732370 100644
--- a/src/type_determiner.cc
+++ b/src/type_determiner.cc
@@ -400,12 +400,17 @@
   if (data_type->IsVector()) {
     auto* vec = data_type->AsVector();
 
-    // The vector will have a number of components equal to the length of the
-    // swizzle. This assumes the validator will check that the swizzle
-    // is correct.
-    expr->set_result_type(
-        ctx_.type_mgr().Get(std::make_unique<ast::type::VectorType>(
-            vec->type(), expr->member()->name().size())));
+    auto size = expr->member()->name().size();
+    if (size == 1) {
+      // A single element swizzle is just the type of the vector.
+      expr->set_result_type(vec->type());
+    } else {
+      // The vector will have a number of components equal to the length of the
+      // swizzle. This assumes the validator will check that the swizzle
+      // is correct.
+      expr->set_result_type(ctx_.type_mgr().Get(
+          std::make_unique<ast::type::VectorType>(vec->type(), size)));
+    }
     return true;
   }