Rename ParamList to TuplePattern (#3479)

Co-authored-by: Richard Smith <richard@metafoo.co.uk>

toolchain/check/handle_pattern_list.cpp

@@ -0,0 +1,62 @@
+// 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/check/context.h"
+
+namespace Carbon::Check {
+
+auto HandleImplicitParamList(Context& context, Parse::NodeId parse_node)
+    -> bool {
+  auto refs_id = context.ParamOrArgEnd(Parse::NodeKind::ImplicitParamListStart);
+  context.node_stack()
+      .PopAndDiscardSoloParseNode<Parse::NodeKind::ImplicitParamListStart>();
+  context.node_stack().Push(parse_node, refs_id);
+  // The implicit parameter list's scope extends to the end of the following
+  // parameter list.
+  return true;
+}
+
+auto HandleImplicitParamListStart(Context& context, Parse::NodeId parse_node)
+    -> bool {
+  context.PushScope();
+  context.node_stack().Push(parse_node);
+  context.ParamOrArgStart();
+  return true;
+}
+
+auto HandleTuplePattern(Context& context, Parse::NodeId parse_node) -> bool {
+  auto refs_id = context.ParamOrArgEnd(Parse::NodeKind::TuplePatternStart);
+  context.PopScope();
+  context.node_stack()
+      .PopAndDiscardSoloParseNode<Parse::NodeKind::TuplePatternStart>();
+  context.node_stack().Push(parse_node, refs_id);
+  return true;
+}
+
+auto HandlePatternListComma(Context& context, Parse::NodeId /*parse_node*/)
+    -> bool {
+  context.ParamOrArgComma();
+  return true;
+}
+
+auto HandleTuplePatternStart(Context& context, Parse::NodeId parse_node)
+    -> bool {
+  // A tuple pattern following an implicit parameter list shares the same
+  // scope.
+  //
+  // TODO: For a declaration like
+  //
+  //   fn A(T:! type).B(U:! T).C(x: X(U)) { ... }
+  //
+  // ... all the earlier parameter should be in scope in the later parameter
+  // lists too.
+  if (!context.node_stack().PeekIs<Parse::NodeKind::ImplicitParamList>()) {
+    context.PushScope();
+  }
+  context.node_stack().Push(parse_node);
+  context.ParamOrArgStart();
+  return true;
+}
+
+}  // namespace Carbon::Check