From 8280be1c36a5df2ef728a286078de2d69639e971 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard@metafoo.co.uk>
Date: Fri, 16 Apr 2021 16:21:41 -0700
Subject: [PATCH] Factor statement parsing out of code block parsing.

---
 parser/parser_impl.cpp | 57 ++++++++++++++++++------------------------
 parser/parser_impl.h   |  3 +++
 2 files changed, 27 insertions(+), 33 deletions(-)

diff --git a/parser/parser_impl.cpp b/parser/parser_impl.cpp
index c2bd043408ae..f099e98fdd42 100644
--- a/parser/parser_impl.cpp
+++ b/parser/parser_impl.cpp
@@ -327,40 +327,16 @@ auto ParseTree::Parser::ParseCodeBlock() -> Node {
   bool has_errors = false;
 
   // Loop over all the different possibly nested elements in the code block.
-  for (;;) {
-    switch (tokens.GetKind(*position)) {
-      case TokenKind::VarKeyword():
-        ParseVariableDeclaration();
-        continue;
-
-      default:
-        // A statement with no introducer token can only be an expression
-        // statement.
-        if (ParseExpressionStatement()) {
-          continue;
-        }
-
-        // We detected and diagnosed an error of some kind. We can trivially
-        // skip to the actual close curly brace from here.
-        // FIXME: It would be better to skip to the next semicolon, or the next
-        // token at the start of a line with the same indent as this one.
-        SkipTo(tokens.GetMatchedClosingToken(open_curly));
-        has_errors = true;
-        // Now fall through to the close curly brace handling code.
-        LLVM_FALLTHROUGH;
-
-      case TokenKind::CloseCurlyBrace():
-        break;
-
-      case TokenKind::OpenCurlyBrace():
-        // FIXME: We should consider avoiding recursion here with some side
-        // stack.
-        ParseCodeBlock();
-        continue;
+  while (tokens.GetKind(*position) != TokenKind::CloseCurlyBrace()) {
+    if (!ParseStatement()) {
+      // We detected and diagnosed an error of some kind. We can trivially skip
+      // to the actual close curly brace from here.
+      // FIXME: It would be better to skip to the next semicolon, or the next
+      // token at the start of a line with the same indent as this one.
+      SkipTo(tokens.GetMatchedClosingToken(open_curly));
+      has_errors = true;
+      break;
     }
-
-    // We only continue looping with `continue` above.
-    break;
   }
 
   // We always reach here having set our position in the token stream to the
@@ -736,4 +712,19 @@ auto ParseTree::Parser::ParseExpressionStatement() -> llvm::Optional<Node> {
   return llvm::None;
 }
 
+auto ParseTree::Parser::ParseStatement() -> llvm::Optional<Node> {
+  switch (tokens.GetKind(*position)) {
+    case TokenKind::VarKeyword():
+      return ParseVariableDeclaration();
+
+    case TokenKind::OpenCurlyBrace():
+      return ParseCodeBlock();
+
+    default:
+      // A statement with no introducer token can only be an expression
+      // statement.
+      return ParseExpressionStatement();
+  }
+}
+
 }  // namespace Carbon
diff --git a/parser/parser_impl.h b/parser/parser_impl.h
index 57fd8d3ba588..ea07909e743d 100644
--- a/parser/parser_impl.h
+++ b/parser/parser_impl.h
@@ -171,6 +171,9 @@ class ParseTree::Parser {
   // Parses an expression statement: an expression followed by a semicolon.
   auto ParseExpressionStatement() -> llvm::Optional<Node>;
 
+  // Parses a statement.
+  auto ParseStatement() -> llvm::Optional<Node>;
+
   ParseTree& tree;
   TokenizedBuffer& tokens;
   TokenDiagnosticEmitter& emitter;