From bd145d2c6ae5b4b0a7a388881862fa2b9ffbf5a3 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Tue, 26 Aug 2014 23:22:18 -0700
Subject: [PATCH] Preserve the initial error node in handle_error function

---
 include/tree_sitter/parser.h | 12 +++++++---
 src/runtime/lexer.c          |  6 ++---
 src/runtime/parser.c         | 46 +++++++++++++++++-------------------
 3 files changed, 33 insertions(+), 31 deletions(-)

diff --git a/include/tree_sitter/parser.h b/include/tree_sitter/parser.h
index 419f4a1a..7ce0d3ca 100644
--- a/include/tree_sitter/parser.h
+++ b/include/tree_sitter/parser.h
@@ -21,7 +21,6 @@ typedef struct TSLexer {
   size_t position_in_chunk;
   size_t token_end_position;
   size_t token_start_position;
-  int reached_end;
 
   TSTree *(*accept_fn)(struct TSLexer *, TSSymbol, int);
   int (*advance_fn)(struct TSLexer *);
@@ -48,6 +47,10 @@ static inline TSTree *ts_lexer_accept(TSLexer *lexer, TSSymbol symbol,
   return lexer->accept_fn(lexer, symbol, is_hidden);
 }
 
+static inline int ts_lexer_is_done(const TSLexer *lexer) {
+  return lexer->chunk_size == 0 && lexer->position_in_chunk > 0;
+}
+
 typedef unsigned short TSStateId;
 
 typedef enum {
@@ -108,8 +111,11 @@ struct TSLanguage {
 #define ADVANCE(state_index)              \
   {                                       \
     DEBUG_LEX("ADVANCE %d", state_index); \
-    if (!ts_lexer_advance(lexer))         \
-      ACCEPT_TOKEN(ts_builtin_sym_end);   \
+    if (ts_lexer_is_done(lexer)) {        \
+      DEBUG_LEX("END_OF_INPUT");          \
+      return NULL;                        \
+    }                                     \
+    ts_lexer_advance(lexer);              \
     lex_state = state_index;              \
     goto next_state;                      \
   }
diff --git a/src/runtime/lexer.c b/src/runtime/lexer.c
index bff7f0ab..d69fb29b 100644
--- a/src/runtime/lexer.c
+++ b/src/runtime/lexer.c
@@ -2,18 +2,17 @@
 #include "runtime/tree.h"
 
 static int advance(TSLexer *lexer) {
-  static const char *empty_chunk = "";
+  static const char empty_chunk[2] = { '\0', '\0' };
   if (lexer->position_in_chunk + 1 < lexer->chunk_size) {
     lexer->position_in_chunk++;
   } else {
-    if (lexer->reached_end)
+    if (lexer->chunk == empty_chunk)
       return 0;
 
     lexer->chunk_start += lexer->chunk_size;
     lexer->chunk = lexer->input.read_fn(lexer->input.data, &lexer->chunk_size);
     lexer->position_in_chunk = 0;
     if (lexer->chunk_size == 0) {
-      lexer->reached_end = 1;
       lexer->chunk = empty_chunk;
     }
   }
@@ -36,7 +35,6 @@ TSLexer ts_lexer_make() {
                      .position_in_chunk = 0,
                      .token_start_position = 0,
                      .token_end_position = 0,
-                     .reached_end = 0,
                      .advance_fn = advance,
                      .accept_fn = accept, };
 }
diff --git a/src/runtime/parser.c b/src/runtime/parser.c
index 1e70f811..06b39f84 100644
--- a/src/runtime/parser.c
+++ b/src/runtime/parser.c
@@ -51,7 +51,8 @@ static size_t breakdown_stack(TSParser *parser, TSInputEdit *edit) {
 static TSTree *build_error_node(TSParser *parser) {
   TSStateId state = ts_stack_top_state(&parser->stack);
   unsigned char lookahead = ts_lexer_lookahead_char(&parser->lexer);
-  TSSymbol *expected_symbols = malloc(parser->language->symbol_count * sizeof(TSSymbol *));
+  TSSymbol *expected_symbols =
+      malloc(parser->language->symbol_count * sizeof(TSSymbol *));
 
   size_t count = 0;
   const TSParseAction *actions = actions_for_state(parser->language, state);
@@ -114,37 +115,19 @@ static int reduce_extra(TSParser *parser, TSSymbol symbol) {
 }
 
 static void lex(TSParser *parser, TSStateId lex_state) {
-  parser->lookahead = parser->language->lex_fn(
-      &parser->lexer, lex_state);
+  if (parser->lookahead)
+    ts_tree_release(parser->lookahead);
+  parser->lookahead = parser->language->lex_fn(&parser->lexer, lex_state);
   if (!parser->lookahead) {
     parser->lookahead = build_error_node(parser);
   }
 }
 
 static int handle_error(TSParser *parser) {
-  TSTree *error = build_error_node(parser);
+  TSTree *error = parser->lookahead;
+  ts_tree_retain(error);
 
-  /*
-   *  Run the lexer until it produces a token that allows for
-   *  error recovery.
-   */
   for (;;) {
-    ts_tree_release(parser->lookahead);
-    size_t prev_position = ts_lexer_position(&parser->lexer);
-    lex(parser, ts_lex_state_error);
-
-    /*
-     *  If no characters are consumed, advance the lexer to the next
-     *  character.
-     */
-    int at_end = 0;
-    if (ts_lexer_position(&parser->lexer) == prev_position)
-      at_end = !ts_lexer_advance(&parser->lexer);
-
-    if (at_end || parser->lookahead->symbol == ts_builtin_sym_end) {
-      ts_stack_push(&parser->stack, 0, error);
-      return 0;
-    }
 
     /*
      *  Unwind the parse stack until a state is found in which an error is
@@ -163,10 +146,25 @@ static int handle_error(TSParser *parser) {
         if (action_after_error.type != TSParseActionTypeError) {
           ts_stack_shrink(&parser->stack, i + 1);
           ts_stack_push(&parser->stack, state_after_error, error);
+          ts_tree_release(error);
           return 1;
         }
       }
     }
+
+    /*
+     *  If there is no state in the stack for which we can recover with the
+     *  current lookahead token, advance to the next token. If no characters
+     *  were consumed, advance the lexer to the next character.
+     */
+    size_t prev_position = ts_lexer_position(&parser->lexer);
+    lex(parser, ts_lex_state_error);
+    if (ts_lexer_position(&parser->lexer) == prev_position)
+      if (!ts_lexer_advance(&parser->lexer)) {
+        ts_stack_push(&parser->stack, 0, error);
+        ts_tree_release(error);
+        return 0;
+      }
   }
 }