Emit UnaryDerivative in WGSL writer.

This CL updates the WGSL writer to emit the unary derivative expression.

Bug: tint:4
Change-Id: I18c0fd56d88f98a6c5d37e176d98ab7b3077a50c
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17120
Reviewed-by: David Neto <dneto@google.com>

src/CMakeLists.txt

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 97c9a32..e8c005c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -416,6 +416,7 @@
     writer/wgsl/generator_impl_member_accessor_test.cc
     writer/wgsl/generator_impl_relational_test.cc
     writer/wgsl/generator_impl_type_test.cc
+    writer/wgsl/generator_impl_unary_derivative_test.cc
     writer/wgsl/generator_impl_variable_test.cc
   )
 endif()

src/writer/wgsl/generator_impl.cc

diff --git a/src/writer/wgsl/generator_impl.cc b/src/writer/wgsl/generator_impl.cc
index f60126e..9e6a1be 100644
--- a/src/writer/wgsl/generator_impl.cc
+++ b/src/writer/wgsl/generator_impl.cc
@@ -44,6 +44,7 @@
 #include "src/ast/type/vector_type.h"
 #include "src/ast/type_initializer_expression.h"
 #include "src/ast/uint_literal.h"
+#include "src/ast/unary_derivative_expression.h"
 
 namespace tint {
 namespace writer {
@@ -144,6 +145,9 @@
   if (expr->IsRelational()) {
     return EmitRelational(expr->AsRelational());
   }
+  if (expr->IsUnaryDerivative()) {
+    return EmitUnaryDerivative(expr->AsUnaryDerivative());
+  }
 
   error_ = "unknown expression type";
   return false;
@@ -535,6 +539,33 @@
   return true;
 }
 
+bool GeneratorImpl::EmitUnaryDerivative(ast::UnaryDerivativeExpression* expr) {
+  switch (expr->op()) {
+    case ast::UnaryDerivative::kDpdx:
+      out_ << "dpdx";
+      break;
+    case ast::UnaryDerivative::kDpdy:
+      out_ << "dpdy";
+      break;
+    case ast::UnaryDerivative::kFwidth:
+      out_ << "fwidth";
+      break;
+  }
+
+  if (expr->modifier() != ast::DerivativeModifier::kNone) {
+    out_ << "<" << expr->modifier() << ">";
+  }
+
+  out_ << "(";
+
+  if (!EmitExpression(expr->param())) {
+    return false;
+  }
+
+  out_ << ")";
+  return true;
+}
+
 }  // namespace wgsl
 }  // namespace writer
 }  // namespace tint

src/writer/wgsl/generator_impl.h

diff --git a/src/writer/wgsl/generator_impl.h b/src/writer/wgsl/generator_impl.h
index 698de59..c2836a2 100644
--- a/src/writer/wgsl/generator_impl.h
+++ b/src/writer/wgsl/generator_impl.h
@@ -126,6 +126,10 @@
   /// @param expr the type initializer expression
   /// @returns true if the initializer is emitted
   bool EmitTypeInitializer(ast::TypeInitializerExpression* expr);
+  /// Handles a unary derivative expression
+  /// @param expr the expression to emit
+  /// @returns true if the expressionw as emitted
+  bool EmitUnaryDerivative(ast::UnaryDerivativeExpression* expr);
   /// Handles generating a variable
   /// @param var the variable to generate
   /// @returns true if the variable was emitted

src/writer/wgsl/generator_impl_unary_derivative_test.cc

diff --git a/src/writer/wgsl/generator_impl_unary_derivative_test.cc b/src/writer/wgsl/generator_impl_unary_derivative_test.cc
new file mode 100644
index 0000000..b7af8dc
--- /dev/null
+++ b/src/writer/wgsl/generator_impl_unary_derivative_test.cc
@@ -0,0 +1,83 @@
+// Copyright 2020 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <memory>
+
+#include "gtest/gtest.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/unary_derivative_expression.h"
+#include "src/writer/wgsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace wgsl {
+namespace {
+
+struct UnaryDerivativeData {
+  const char* name;
+  ast::UnaryDerivative derivative;
+};
+inline std::ostream& operator<<(std::ostream& out, UnaryDerivativeData data) {
+  out << data.derivative;
+  return out;
+}
+using UnaryDerivativeTest = testing::TestWithParam<UnaryDerivativeData>;
+TEST_P(UnaryDerivativeTest, Emit_ModifierNone) {
+  auto params = GetParam();
+
+  auto expr = std::make_unique<ast::IdentifierExpression>("expr");
+
+  ast::UnaryDerivativeExpression derivative(
+      params.derivative, ast::DerivativeModifier::kNone, std::move(expr));
+
+  GeneratorImpl g;
+  ASSERT_TRUE(g.EmitExpression(&derivative)) << g.error();
+  EXPECT_EQ(g.result(), std::string(params.name) + "(expr)");
+}
+TEST_P(UnaryDerivativeTest, Emit_ModifierFine) {
+  auto params = GetParam();
+
+  auto expr = std::make_unique<ast::IdentifierExpression>("expr");
+
+  ast::UnaryDerivativeExpression derivative(
+      params.derivative, ast::DerivativeModifier::kFine, std::move(expr));
+
+  GeneratorImpl g;
+  ASSERT_TRUE(g.EmitExpression(&derivative)) << g.error();
+  EXPECT_EQ(g.result(), std::string(params.name) + "<fine>(expr)");
+}
+TEST_P(UnaryDerivativeTest, Emit_ModifierCoarse) {
+  auto params = GetParam();
+
+  auto expr = std::make_unique<ast::IdentifierExpression>("expr");
+
+  ast::UnaryDerivativeExpression derivative(
+      params.derivative, ast::DerivativeModifier::kCoarse, std::move(expr));
+
+  GeneratorImpl g;
+  ASSERT_TRUE(g.EmitExpression(&derivative)) << g.error();
+  EXPECT_EQ(g.result(), std::string(params.name) + "<coarse>(expr)");
+}
+INSTANTIATE_TEST_SUITE_P(
+    GeneratorImplTest,
+    UnaryDerivativeTest,
+    testing::Values(UnaryDerivativeData{"dpdx", ast::UnaryDerivative::kDpdx},
+                    UnaryDerivativeData{"dpdy", ast::UnaryDerivative::kDpdy},
+                    UnaryDerivativeData{"fwidth",
+                                        ast::UnaryDerivative::kFwidth}));
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace writer
+}  // namespace tint