Rename files to use abbreviations (#3389)

Reflects these recent PRs:
* #3375 
* #3382

toolchain/parse/handle_paren_expr.cpp

@@ -0,0 +1,80 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/parse/context.h"
+
+namespace Carbon::Parse {
+
+auto HandleParenExpr(Context& context) -> void {
+  auto state = context.PopState();
+
+  // Advance past the open paren.
+  context.AddLeafNode(NodeKind::ParenExprOrTupleLiteralStart,
+                      context.ConsumeChecked(Lex::TokenKind::OpenParen));
+
+  if (context.PositionIs(Lex::TokenKind::CloseParen)) {
+    state.state = State::ParenExprFinishAsTuple;
+    context.PushState(state);
+  } else {
+    state.state = State::ParenExprFinishAsNormal;
+    context.PushState(state);
+    context.PushState(State::ParenExprParameterFinishAsUnknown);
+    context.PushState(State::Expr);
+  }
+}
+
+// Handles ParenExprParameterFinishAs(Unknown|Tuple).
+static auto HandleParenExprParameterFinish(Context& context, bool as_tuple)
+    -> void {
+  auto state = context.PopState();
+
+  auto list_token_kind = context.ConsumeListToken(
+      NodeKind::TupleLiteralComma, Lex::TokenKind::CloseParen, state.has_error);
+  if (list_token_kind == Context::ListTokenKind::Close) {
+    return;
+  }
+
+  // If this is the first item and a comma was found, switch to tuple handling.
+  // Note this could be `(expr,)` so we may not reuse the current state, but
+  // it's still necessary to switch the parent.
+  if (!as_tuple) {
+    state.state = State::ParenExprParameterFinishAsTuple;
+
+    auto finish_state = context.PopState();
+    CARBON_CHECK(finish_state.state == State::ParenExprFinishAsNormal)
+        << "Unexpected parent state, found: " << finish_state.state;
+    finish_state.state = State::ParenExprFinishAsTuple;
+    context.PushState(finish_state);
+  }
+
+  // On a comma, push another expression handler.
+  if (list_token_kind == Context::ListTokenKind::Comma) {
+    context.PushState(state);
+    context.PushState(State::Expr);
+  }
+}
+
+auto HandleParenExprParameterFinishAsUnknown(Context& context) -> void {
+  HandleParenExprParameterFinish(context, /*as_tuple=*/false);
+}
+
+auto HandleParenExprParameterFinishAsTuple(Context& context) -> void {
+  HandleParenExprParameterFinish(context, /*as_tuple=*/true);
+}
+
+auto HandleParenExprFinishAsNormal(Context& context) -> void {
+  auto state = context.PopState();
+
+  context.AddNode(NodeKind::ParenExpr, context.Consume(), state.subtree_start,
+                  state.has_error);
+}
+
+auto HandleParenExprFinishAsTuple(Context& context) -> void {
+  auto state = context.PopState();
+
+  context.AddNode(NodeKind::TupleLiteral, context.Consume(),
+                  state.subtree_start, state.has_error);
+}
+
+}  // namespace Carbon::Parse