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cql: Eagerly throw lexing and parsing exceptions

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Previously, lexing and parsing errors were aggregated while CQL queries were
evaluated. Afterwards, the first collected error (if present) would be thrown as
an exception.

The problem was that when parsing and lexing errors were aggregated this way,
the parser would continue even in spite of errors like "no viable alternative".
Semantic actions attached to grammar rules would still execute, though with
variables that had not yet been initialized. This would crash Scylla.

This change modifies the error-handling strategy of CQL parsing. Rather than
aggregate errors, we throw an exception on the first error we encounter. This
ensures that grammar actions never execute unless there is a precise match.

One possible issue with this approach is that the generated C++ code from the
ANTLR grammar may not be exception-safe. I compiled Scylla in debug-mode with
ASan support and executed several erroneous CQL queries with `cqlsh`. No memory
leaks were reported.

Fixes #2466.

Signed-off-by: Jesse Haber-Kucharsky <jhaberku@scylladb.com>
Message-Id: <db1f650a2bbb615b506d9015486eece45375a440.1498836703.git.jhaberku@scylladb.com>
This commit is contained in:
Jesse Haber-Kucharsky
2017-06-30 11:32:56 -04:00
committed by Avi Kivity
parent 9fa855e105
commit 1100bb8a5b
2 changed files with 8 additions and 18 deletions
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24
cql3/error_collector.hh
View File

@@ -67,10 +67,6 @@ class error_collector : public error_listener<RecognizerType, ExceptionBaseType>
*/
const sstring_view _query;
/**
* The error messages.
*/
std::vector<sstring> _error_msgs;
public:
/**
@@ -81,7 +77,10 @@ public:
*/
error_collector(const sstring_view& query) : _query(query) {}
virtual void syntax_error(RecognizerType& recognizer, ANTLR_UINT8** token_names, ExceptionBaseType* ex) override {
/**
* Format and throw a new \c exceptions::syntax_exception.
*/
[[noreturn]] virtual void syntax_error(RecognizerType& recognizer, ANTLR_UINT8** token_names, ExceptionBaseType* ex) override {
auto hdr = get_error_header(ex);
auto msg = get_error_message(recognizer, ex, token_names);
std::stringstream result;
@@ -90,22 +89,15 @@ public:
if (recognizer instanceof Parser)
appendQuerySnippet((Parser) recognizer, builder);
#endif
_error_msgs.emplace_back(result.str());
}
virtual void syntax_error(RecognizerType& recognizer, const sstring& msg) override {
_error_msgs.emplace_back(msg);
throw exceptions::syntax_exception(result.str());
}
/**
* Throws the first syntax error found by the lexer or the parser if it exists.
*
* @throws SyntaxException the syntax error.
* Throw a new \c exceptions::syntax_exception.
*/
void throw_first_syntax_error() {
if (!_error_msgs.empty()) {
throw exceptions::syntax_exception(_error_msgs[0]);
}
[[noreturn]] virtual void syntax_error(RecognizerType&, const sstring& msg) override {
throw exceptions::syntax_exception(msg);
}
private:

2
cql3/util.hh
View File

@@ -51,8 +51,6 @@ Result do_with_parser(const sstring_view& cql, Func&& f) {
cql3_parser::CqlParser parser{&tstream};
parser.set_error_listener(parser_error_collector);
auto result = f(parser);
lexer_error_collector.throw_first_syntax_error();
parser_error_collector.throw_first_syntax_error();
return result;
}