From 60cccd8e58f2a024676599cc00971a6e406e6d42 Mon Sep 17 00:00:00 2001
From: Philip Herron <philip.herron@embecosm.com>
Date: Mon, 8 Feb 2021 13:26:07 +0000
Subject: Fixes parsing if expressions as part of an expression.

This allows for rust style ternery expressions.

Fixes #214
---
 gcc/rust/parse/rust-parse-impl.h                   | 50 ++++++++++++++++++----
 gcc/rust/parse/rust-parse.h                        |  6 ++-
 .../rust.test/compilable/block_expr_parser_bug.rs  |  4 ++
 3 files changed, 50 insertions(+), 10 deletions(-)
 create mode 100644 gcc/testsuite/rust.test/compilable/block_expr_parser_bug.rs

(limited to 'gcc')

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index ea468ca..906f6b1 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -7504,12 +7504,23 @@ Parser<ManagedTokenSource>::parse_loop_label ()
 template <typename ManagedTokenSource>
 std::unique_ptr<AST::IfExpr>
 Parser<ManagedTokenSource>::parse_if_expr (
-  std::vector<AST::Attribute> outer_attrs ATTRIBUTE_UNUSED)
+  std::vector<AST::Attribute> outer_attrs ATTRIBUTE_UNUSED, bool pratt_parse)
 {
   // TODO: make having outer attributes an error?
-
-  Location locus = lexer.peek_token ()->get_locus ();
-  skip_token (IF);
+  Location locus = Linemap::unknown_location ();
+  if (!pratt_parse)
+    {
+      locus = lexer.peek_token ()->get_locus ();
+      if (!skip_token (IF))
+	{
+	  skip_after_end_block ();
+	  return nullptr;
+	}
+    }
+  else
+    {
+      locus = lexer.peek_token ()->get_locus () - 1;
+    }
 
   // detect accidental if let
   if (lexer.peek_token ()->get_id () == LET)
@@ -7640,12 +7651,23 @@ Parser<ManagedTokenSource>::parse_if_expr (
 template <typename ManagedTokenSource>
 std::unique_ptr<AST::IfLetExpr>
 Parser<ManagedTokenSource>::parse_if_let_expr (
-  std::vector<AST::Attribute> outer_attrs ATTRIBUTE_UNUSED)
+  std::vector<AST::Attribute> outer_attrs ATTRIBUTE_UNUSED, bool pratt_parse)
 {
   // TODO: make having outer attributes an error?
-
-  Location locus = lexer.peek_token ()->get_locus ();
-  skip_token (IF);
+  Location locus = Linemap::unknown_location ();
+  if (!pratt_parse)
+    {
+      locus = lexer.peek_token ()->get_locus ();
+      if (!skip_token (IF))
+	{
+	  skip_after_end_block ();
+	  return nullptr;
+	}
+    }
+  else
+    {
+      locus = lexer.peek_token ()->get_locus () - 1;
+    }
 
   // detect accidental if expr parsed as if let expr
   if (lexer.peek_token ()->get_id () != LET)
@@ -12399,6 +12421,18 @@ Parser<ManagedTokenSource>::null_denotation (
     case LEFT_CURLY:
       // ok - this is an expression with block for once.
       return parse_block_expr (std::move (outer_attrs), true);
+    case IF:
+      // if or if let, so more lookahead to find out
+      if (lexer.peek_token (1)->get_id () == LET)
+	{
+	  // if let expr
+	  return parse_if_let_expr (std::move (outer_attrs), true);
+	}
+      else
+	{
+	  // if expr
+	  return parse_if_expr (std::move (outer_attrs), true);
+	}
     case MATCH_TOK:
       // also an expression with block
       return parse_match_expr (std::move (outer_attrs), true);
diff --git a/gcc/rust/parse/rust-parse.h b/gcc/rust/parse/rust-parse.h
index 2778ec7..aeda82b 100644
--- a/gcc/rust/parse/rust-parse.h
+++ b/gcc/rust/parse/rust-parse.h
@@ -480,10 +480,12 @@ private:
 		    bool pratt_parse = false);
   std::unique_ptr<AST::IfExpr>
   parse_if_expr (std::vector<AST::Attribute> outer_attrs
-		 = std::vector<AST::Attribute> ());
+		 = std::vector<AST::Attribute> (),
+		 bool pratt_parse = false);
   std::unique_ptr<AST::IfLetExpr>
   parse_if_let_expr (std::vector<AST::Attribute> outer_attrs
-		     = std::vector<AST::Attribute> ());
+		     = std::vector<AST::Attribute> (),
+		     bool pratt_parse = false);
   std::unique_ptr<AST::LoopExpr>
   parse_loop_expr (std::vector<AST::Attribute> outer_attrs
 		   = std::vector<AST::Attribute> (),
diff --git a/gcc/testsuite/rust.test/compilable/block_expr_parser_bug.rs b/gcc/testsuite/rust.test/compilable/block_expr_parser_bug.rs
new file mode 100644
index 0000000..e583008
--- /dev/null
+++ b/gcc/testsuite/rust.test/compilable/block_expr_parser_bug.rs
@@ -0,0 +1,4 @@
+fn main() {
+    let a = 123;
+    let b = if a > 10 { a - 1 } else { a + 1 };
+}
-- 
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