From 24a44ffdd6e5648b3e0528ac3ccc871da853158c Mon Sep 17 00:00:00 2001
From: Tim Foley <tfoley@nvidia.com>
Date: Tue, 11 Jul 2017 15:43:18 -0700
Subject: Make parser recovering more robust to avoid infinite loops

Fixes #75

In order to avoid cascaded errors, I went ahead and made the parser refuse to skip past a `}` in recovery mode. The problem with this is that we fail to make forward progress if we are stuck on a `}` (this happens if you have an extra `}` at the global scope.
---
 source/slang/parser.cpp | 51 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 42 insertions(+), 9 deletions(-)

(limited to 'source/slang/parser.cpp')

diff --git a/source/slang/parser.cpp b/source/slang/parser.cpp
index 759fc0c20..de63793b1 100644
--- a/source/slang/parser.cpp
+++ b/source/slang/parser.cpp
@@ -303,17 +303,40 @@ namespace Slang
         if (!parser->isRecovering)
             return true;
 
-        // Determine if we are looking for a closing token at all...
-        bool lookingForClose = false;
+        // Determine if we are looking for common closing tokens,
+        // so that we can know whether or we are allowed to skip
+        // over them.
+
+        bool lookingForEOF = false;
+        bool lookingForRCurly = false;
+        bool lookingForRParen = false;
+        bool lookingForRSquare = false;
+
         for (int ii = 0; ii < recoverBeforeCount; ++ii)
         {
-            if (IsClosingToken(recoverBefore[ii]))
-                lookingForClose = true;
+            switch (recoverBefore[ii])
+            {
+            default:
+                break;
+
+            case TokenType::EndOfFile:  lookingForEOF       = true; break;
+            case TokenType::RBrace:     lookingForRCurly    = true; break;
+            case TokenType::RParent:    lookingForRParen    = true; break;
+            case TokenType::RBracket:   lookingForRSquare   = true; break;
+            }
         }
         for (int ii = 0; ii < recoverAfterCount; ++ii)
         {
-            if (IsClosingToken(recoverAfter[ii]))
-                lookingForClose = true;
+            switch (recoverBefore[ii])
+            {
+            default:
+                break;
+
+            case TokenType::EndOfFile:  lookingForEOF       = true; break;
+            case TokenType::RBrace:     lookingForRCurly    = true; break;
+            case TokenType::RParent:    lookingForRParen    = true; break;
+            case TokenType::RBracket:   lookingForRSquare   = true; break;
+            }
         }
 
         TokenReader* tokenReader = &parser->tokenReader;
@@ -354,12 +377,23 @@ namespace Slang
             // we are looking for a closing token
             case TokenType::RParent:
             case TokenType::RBracket:
-                if (!lookingForClose)
+                if (lookingForRParen || lookingForRSquare || lookingForRCurly || lookingForEOF)
+                {
+                    // We are looking for a closing token, so it is okay to skip these
+                }
+                else
                     return false;
                 break;
 
-            // never skip a `}`, to avoid spurious errors
+            // Don't skip a `}`, to avoid spurious errors,
+            // with the exception of when we are looking for EOF
             case TokenType::RBrace:
+                if (lookingForRCurly || lookingForEOF)
+                {
+                    // We are looking for end-of-file, so it is okay to skip here
+                }
+                else
+
                 return false;
             }
 
@@ -2342,7 +2376,6 @@ namespace Slang
         while(!AdvanceIfMatch(parser, closingToken))
         {
             ParseDecl(parser, containerDecl);
-            TryRecover(parser);
         }
     }
 
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