Fix FP memleak with outparam allocation (f'up to #12186) (#5677)

I wonder if it is worth trying to get this right. We also have FPs when
the return value is assigned to a variable, and that seems much harder
to fix.

lib/checkleakautovar.cpp

@@ -1108,6 +1108,23 @@ void CheckLeakAutoVar::ret(const Token *tok, VarInfo &varInfo, const bool isEndO
                 }
             }
 
+            // don't warn when returning after checking return value of outparam allocation
+            const Scope* scope = tok->scope();
+            if (scope->type == Scope::ScopeType::eIf || scope->type== Scope::ScopeType::eElse) {
+                if (scope->type == Scope::ScopeType::eElse) {
+                    scope = scope->bodyStart->tokAt(-2)->scope();
+                }
+                const Token* const ifEnd = scope->bodyStart->previous();
+                const Token* const ifStart = ifEnd->link();
+                const Token* const alloc = it->second.allocTok;
+                if (precedes(ifStart, alloc) && succeeds(ifEnd, alloc)) {
+                    int argn{};
+                    if (const Token* ftok = getTokenArgumentFunction(alloc, argn))
+                        if (Token::Match(ftok->next()->astParent(), "%comp%"))
+                            continue;
+                }
+            }
+
             // return deallocated pointer
             if (used != PtrUsage::NONE && it->second.status == VarInfo::DEALLOC)
                 deallocReturnError(tok, it->second.allocTok, var->name());

test/cfg/gnu.c

@@ -380,6 +380,24 @@ void memleak_asprintf5(char* p) {
     // cppcheck-suppress memleak
 }
 
+void memleak_asprintf6(const char* fmt, const int arg) {
+    char* ptr;
+    if (-1 == asprintf(&ptr, fmt, arg))
+        return;
+    printf("%s", ptr);
+    free(ptr);
+}
+
+void memleak_asprintf7(const char* fmt, const int arg) {
+    char* ptr;
+    if (asprintf(&ptr, fmt, arg) != -1) {
+        printf("%s", ptr);
+        free(ptr);
+    }
+    else
+        return;
+}
+
 void memleak_xmalloc()
 {
     char *p = (char*)xmalloc(10);