Add assignment statement type determination.

This CL adds type determination for the assignment statements.

Bug: tint:5
Change-Id: Ica0e59a459bfedc0c649d279f93a31b188c27736
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/18828
Reviewed-by: David Neto <dneto@google.com>

src/type_determiner.cc

diff --git a/src/type_determiner.cc b/src/type_determiner.cc
index c911281..87bf07a 100644
--- a/src/type_determiner.cc
+++ b/src/type_determiner.cc
@@ -14,6 +14,7 @@
 
 #include "src/type_determiner.h"
 
+#include "src/ast/assignment_statement.h"
 #include "src/ast/scalar_constructor_expression.h"
 #include "src/ast/type_constructor_expression.h"
 
@@ -69,7 +70,12 @@
   return true;
 }
 
-bool TypeDeterminer::DetermineResultType(ast::Statement*) {
+bool TypeDeterminer::DetermineResultType(ast::Statement* stmt) {
+  if (stmt->IsAssign()) {
+    auto a = stmt->AsAssign();
+    return DetermineResultType(a->lhs()) && DetermineResultType(a->rhs());
+  }
+
   error_ = "unknown statement type for type determination";
   return false;
 }

src/type_determiner_test.cc

diff --git a/src/type_determiner_test.cc b/src/type_determiner_test.cc
index 49a9c89..471b9a1 100644
--- a/src/type_determiner_test.cc
+++ b/src/type_determiner_test.cc
@@ -18,10 +18,12 @@
 #include <utility>
 
 #include "gtest/gtest.h"
+#include "src/ast/assignment_statement.h"
 #include "src/ast/float_literal.h"
 #include "src/ast/int_literal.h"
 #include "src/ast/scalar_constructor_expression.h"
 #include "src/ast/type/f32_type.h"
+#include "src/ast/type/i32_type.h"
 #include "src/ast/type/vector_type.h"
 #include "src/ast/type_constructor_expression.h"
 
@@ -39,6 +41,28 @@
   std::unique_ptr<TypeDeterminer> td_;
 };
 
+TEST_F(TypeDeterminerTest, Stmt_Assign) {
+  ast::type::F32Type f32;
+  ast::type::I32Type i32;
+
+  auto lhs = std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::IntLiteral>(&i32, 2));
+  auto lhs_ptr = lhs.get();
+
+  auto rhs = std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 2.3f));
+  auto rhs_ptr = rhs.get();
+
+  ast::AssignmentStatement assign(std::move(lhs), std::move(rhs));
+
+  EXPECT_TRUE(td()->DetermineResultType(&assign));
+  ASSERT_NE(lhs_ptr->result_type(), nullptr);
+  ASSERT_NE(rhs_ptr->result_type(), nullptr);
+
+  EXPECT_TRUE(lhs_ptr->result_type()->IsI32());
+  EXPECT_TRUE(rhs_ptr->result_type()->IsF32());
+}
+
 TEST_F(TypeDeterminerTest, Expr_Constructor_Scalar) {
   ast::type::F32Type f32;
   ast::ScalarConstructorExpression s(