Cleanup Lexer (#466)

* Add class LexerSource: it encapsulates reading data from a source,
  either buffer or file.
* Add class LexerSourceLineFinder: it uses a LexerSource to read a line
  from the source for displaying in errors. It lazily caches line
  numbers -> file offsets, so no work is done unless an error occurs.
* Make WastLexer a class instead of a struct.

1 files changed, 8 insertions, 13 deletions

diff --git a/src/wast-parser-lexer-shared.cc b/src/wast-parser-lexer-shared.cc
index e073a369..fe785fe8 100644
--- a/src/wast-parser-lexer-shared.cc
+++ b/src/wast-parser-lexer-shared.cc
@@ -50,25 +50,20 @@ void wast_format_error(SourceErrorHandler* error_handler,
     len = wabt_vsnprintf(buffer, len + 1, format, args_copy);
   }
 
-  char* source_line = nullptr;
-  size_t source_line_length = 0;
-  int source_line_column_offset = 0;
-  size_t source_line_max_length = error_handler->source_line_max_length();
+  LexerSourceLineFinder::SourceLine source_line;
   if (loc && lexer) {
-    source_line = static_cast<char*>(alloca(source_line_max_length + 1));
-    Result result = wast_lexer_get_source_line(
-        lexer, loc, source_line_max_length, source_line, &source_line_length,
-        &source_line_column_offset);
+    size_t source_line_max_length = error_handler->source_line_max_length();
+    Result result = lexer->line_finder().GetSourceLine(
+        *loc, source_line_max_length, &source_line);
     if (WABT_FAILED(result)) {
-      /* if this fails, it means that we've probably screwed up the lexer. blow
-       * up. */
+      // If this fails, it means that we've probably screwed up the lexer. Blow
+      // up.
       WABT_FATAL("error getting the source line.\n");
     }
   }
 
-  error_handler->OnError(loc, std::string(buffer),
-                         std::string(source_line, source_line_length),
-                         source_line_column_offset);
+  error_handler->OnError(loc, std::string(buffer), source_line.line,
+                         source_line.column_offset);
   va_end(args_copy);
 }