Unify the JavaScript parsing recursion checks

We only need to check in one central location and we can allow for more
recursion. 4k recursions seem tolerable. A common default for stack
sizes is 8MB. Each recursion step takes up to 1k stack space in debug
mode. So, exhausting this would burn about half of the available stack
size. We don't report the exact source location in this case as finding
the source location may itself trigger a deep recursion.

Fixes: QTBUG-74087
Change-Id: I43e6e20b322f6035c7136a6f381230ec285c30ae
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 7 insertions, 20 deletions

diff --git a/src/qml/compiler/qv4compilerscanfunctions.cpp b/src/qml/compiler/qv4compilerscanfunctions.cpp
index e0eaa8867b..04593f202a 100644
--- a/src/qml/compiler/qv4compilerscanfunctions.cpp
+++ b/src/qml/compiler/qv4compilerscanfunctions.cpp
@@ -57,7 +57,8 @@ using namespace QV4::Compiler;
 using namespace QQmlJS::AST;
 
 ScanFunctions::ScanFunctions(Codegen *cg, const QString &sourceCode, ContextType defaultProgramType)
-    : _cg(cg)
+    : QQmlJS::AST::Visitor(cg->recursionDepth())
+    , _cg(cg)
     , _sourceCode(sourceCode)
     , _context(nullptr)
     , _allowFuncDecls(true)
@@ -96,25 +97,6 @@ void ScanFunctions::leaveEnvironment()
     _context = _contextStack.isEmpty() ? nullptr : _contextStack.top();
 }
 
-bool ScanFunctions::preVisit(Node *ast)
-{
-    if (_cg->hasError)
-        return false;
-    ++_recursionDepth;
-
-    if (_recursionDepth > 1000) {
-        _cg->throwSyntaxError(ast->lastSourceLocation(), QStringLiteral("Maximum statement or expression depth exceeded"));
-        return false;
-    }
-
-    return true;
-}
-
-void ScanFunctions::postVisit(Node *)
-{
-    --_recursionDepth;
-}
-
 void ScanFunctions::checkDirectivePrologue(StatementList *ast)
 {
     for (StatementList *it = ast; it; it = it->next) {
@@ -893,3 +875,8 @@ void ScanFunctions::calcEscapingVariables()
         }
     }
 }
+
+void ScanFunctions::throwRecursionDepthError()
+{
+    _cg->throwRecursionDepthError();
+}