Fix #15097 (clang import: oob tree index in parseClangAstDump on stray NULL node) (#8903)

Author: Nussu06

lib/clangimport.cpp

@@ -1637,7 +1637,9 @@ void clangimport::parseClangAstDump(Tokenizer &tokenizer, std::istream &f)
         if (pos1 == std::string::npos)
             continue;
         if (!tree.empty() && line.substr(pos1) == "-<<<NULL>>>") {
-            const int level = (pos1 - 1) / 2;
+            const size_t level = (pos1 - 1) / 2;
+            if (level == 0 || level > tree.size())
+                continue;
             tree[level - 1]->children.push_back(nullptr);
             continue;
         }

test/testclangimport.cpp

@@ -140,6 +140,7 @@ class TestClangImport : public TestFixture {
 
         TEST_CASE(crash);
         TEST_CASE(crash2);
+        TEST_CASE(nullNodeInvalidLevel);
     }
 
     std::string parse(const char clang[]) {
@@ -1380,6 +1381,13 @@ class TestClangImport : public TestFixture {
         // out of bounds.
         (void)parse("`-RecordDecl "); // don't crash
     }
+
+    void nullNodeInvalidLevel() {
+        // a "<<<NULL>>>" line whose indentation maps to level 0 must not index tree[-1]
+        const char* clang = "`-FunctionDecl 0x1 <a.cpp:1:1, col:34> col:6 foo 'void ()'\n"
+                            "`-<<<NULL>>>\n";
+        ASSERT_EQUALS("void foo ( ) ;", parse(clang));
+    }
 };
 
 REGISTER_TEST(TestClangImport)