Rename semantic to sem

* Rename namespace semantic to sem
* Rename directory src/semantic/ to src/sem/

Bug: tint:724
Change-Id: I76383b821fbca7f1037a803c497b595a706dcb06
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48120
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/sem/call_target.h

@@ -0,0 +1,102 @@
+// Copyright 2021 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.
+
+#ifndef SRC_SEM_CALL_TARGET_H_
+#define SRC_SEM_CALL_TARGET_H_
+
+#include <vector>
+
+#include "src/sem/node.h"
+#include "src/type/sampler_type.h"
+
+namespace tint {
+
+// Forward declarations
+namespace type {
+class Type;
+}  // namespace type
+
+namespace sem {
+
+/// Parameter describes a single parameter of a call target
+struct Parameter {
+  /// Usage is extra metadata for identifying a parameter based on its overload
+  /// position
+  enum class Usage {
+    kNone,
+    kArrayIndex,
+    kBias,
+    kCoords,
+    kDepthRef,
+    kDdx,
+    kDdy,
+    kLevel,
+    kOffset,
+    kSampler,
+    kSampleIndex,
+    kTexture,
+    kValue,
+  };
+
+  /// Parameter type
+  type::Type* const type;
+  /// Parameter usage
+  Usage const usage = Usage::kNone;
+};
+
+std::ostream& operator<<(std::ostream& out, Parameter parameter);
+
+/// Comparison operator for Parameters
+static inline bool operator==(const Parameter& a, const Parameter& b) {
+  return a.type == b.type && a.usage == b.usage;
+}
+
+/// @returns a string representation of the given parameter usage.
+const char* str(Parameter::Usage usage);
+
+/// ParameterList is a list of Parameter
+using ParameterList = std::vector<Parameter>;
+
+/// @param parameters the list of parameters
+/// @param usage the parameter usage to find
+/// @returns the index of the parameter with the given usage, or -1 if no
+/// parameter with the given usage exists.
+int IndexOf(const ParameterList& parameters, Parameter::Usage usage);
+
+/// CallTarget is the base for callable functions
+class CallTarget : public Castable<CallTarget, Node> {
+ public:
+  /// Constructor
+  /// @param return_type the return type of the call target
+  /// @param parameters the parameters for the call target
+  CallTarget(type::Type* return_type, const ParameterList& parameters);
+
+  /// @return the return type of the call target
+  type::Type* ReturnType() const { return return_type_; }
+
+  /// Destructor
+  ~CallTarget() override;
+
+  /// @return the parameters of the call target
+  const ParameterList& Parameters() const { return parameters_; }
+
+ private:
+  type::Type* const return_type_;
+  ParameterList const parameters_;
+};
+
+}  // namespace sem
+}  // namespace tint
+
+#endif  // SRC_SEM_CALL_TARGET_H_