Add type determination for as expression.

This CL adds the as expression type determination.

Bug: tint:5
Change-Id: I84a06df67844c75112c745f65a2c8102f8677f62
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/18843
Reviewed-by: David Neto <dneto@google.com>

src/type_determiner.cc

@@ -17,6 +17,7 @@
 #include <memory>
 
 #include "src/ast/array_accessor_expression.h"
+#include "src/ast/as_expression.h"
 #include "src/ast/assignment_statement.h"
 #include "src/ast/break_statement.h"
 #include "src/ast/case_statement.h"
@@ -183,6 +184,9 @@ bool TypeDeterminer::DetermineResultType(ast::Expression* expr) {
   if (expr->IsArrayAccessor()) {
     return DetermineArrayAccessor(expr->AsArrayAccessor());
   }
+  if (expr->IsAs()) {
+    return DetermineAs(expr->AsAs());
+  }
   if (expr->IsConstructor()) {
     return DetermineConstructor(expr->AsConstructor());
   }
@@ -215,6 +219,11 @@ bool TypeDeterminer::DetermineArrayAccessor(
   return true;
 }
 
+bool TypeDeterminer::DetermineAs(ast::AsExpression* expr) {
+  expr->set_result_type(expr->type());
+  return true;
+}
+
 bool TypeDeterminer::DetermineConstructor(ast::ConstructorExpression* expr) {
   if (expr->IsTypeConstructor()) {
     expr->set_result_type(expr->AsTypeConstructor()->type());

src/type_determiner.h

@@ -26,6 +26,7 @@ namespace tint {
 namespace ast {
 
 class ArrayAccessorExpression;
+class AsExpression;
 class ConstructorExpression;
 class IdentifierExpression;
 class Function;
@@ -71,6 +72,7 @@ class TypeDeterminer {
 
  private:
   bool DetermineArrayAccessor(ast::ArrayAccessorExpression* expr);
+  bool DetermineAs(ast::AsExpression* expr);
   bool DetermineConstructor(ast::ConstructorExpression* expr);
   bool DetermineIdentifier(ast::IdentifierExpression* expr);
   Context& ctx_;

src/type_determiner_test.cc

@@ -19,6 +19,7 @@
 
 #include "gtest/gtest.h"
 #include "src/ast/array_accessor_expression.h"
+#include "src/ast/as_expression.h"
 #include "src/ast/assignment_statement.h"
 #include "src/ast/break_statement.h"
 #include "src/ast/case_statement.h"
@@ -478,6 +479,16 @@ TEST_F(TypeDeterminerTest, Expr_ArrayAccessor_Vector) {
   EXPECT_TRUE(acc.result_type()->IsF32());
 }
 
+TEST_F(TypeDeterminerTest, Expr_As) {
+  ast::type::F32Type f32;
+  ast::AsExpression as(&f32,
+                       std::make_unique<ast::IdentifierExpression>("name"));
+
+  EXPECT_TRUE(td()->DetermineResultType(&as));
+  ASSERT_NE(as.result_type(), nullptr);
+  EXPECT_TRUE(as.result_type()->IsF32());
+}
+
 TEST_F(TypeDeterminerTest, Expr_Constructor_Scalar) {
   ast::type::F32Type f32;
   ast::ScalarConstructorExpression s(