loplugin:casttovoid: Fix VisitReturnStmt in lambda bodies

...as caused the

assert(!returnTypes_.empty());

in VisitReturnStmt to hit for the return statement in the permutation2D lambda
body (which does not happen to be nested within any other function declaration)
in patch sets 1 and 2 of <https://gerrit.libreoffice.org/c/core/+/113522>
"Compute permutation2D at compile time".

Change-Id: Ic4aa55bef4361e40c2cd6247b5646f7b1ba82e6d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113699
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 38 insertions, 0 deletions

diff --git a/compilerplugins/clang/casttovoid.cxx b/compilerplugins/clang/casttovoid.cxx
index e6da5b6d7445..1717fa09a516 100644
--- a/compilerplugins/clang/casttovoid.cxx
+++ b/compilerplugins/clang/casttovoid.cxx
@@ -169,6 +169,32 @@ public:
         return RecursiveASTVisitor::TraverseConstructorInitializer(init);
     }
 
+    bool TraverseLambdaExpr(LambdaExpr * expr, DataRecursionQueue * queue = nullptr) {
+        if (!shouldTraversePostOrder()) {
+            if (!WalkUpFromLambdaExpr(expr)) {
+                return false;
+            }
+        }
+        auto const n = expr->capture_size();
+        for (unsigned i = 0; i != n; ++i) {
+            auto const c = expr->capture_begin() + i;
+            if (c->isExplicit() || shouldVisitImplicitCode()) {
+                if (!TraverseLambdaCapture(expr, c, expr->capture_init_begin()[i])) {
+                    return false;
+                }
+            }
+        }
+        if (!TraverseCXXRecordDecl(expr->getLambdaClass())) {
+            return false;
+        }
+        if (!queue && shouldTraversePostOrder()) {
+            if (!WalkUpFromLambdaExpr(expr)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     bool VisitDeclRefExpr(DeclRefExpr const * expr) {
         if (ignoreLocation(expr)) {
             return true;
diff --git a/compilerplugins/clang/test/casttovoid.cxx b/compilerplugins/clang/test/casttovoid.cxx
index 9904c8b5a3e4..c3b5eee17c96 100644
--- a/compilerplugins/clang/test/casttovoid.cxx
+++ b/compilerplugins/clang/test/casttovoid.cxx
@@ -73,6 +73,18 @@ int const & fS2_2(S2 const & s) {
     return s.n; // expected-note {{first consumption is here [loplugin:casttovoid]}}
 }
 
+// Don't trigger assert in CastToVoid::VisitReturnStmt:
+int n = [] { return 0; }();
+
+int f() {
+    int n1 = n;
+    int n2 = [](int const & n) -> int const & {
+        (void) n; // expected-error {{unnecessary cast to void [loplugin:casttovoid]}}
+        return n; // expected-note {{first consumption is here [loplugin:casttovoid]}}
+    }(n1);
+    return n2;
+}
+
 int main() {
     int n1 = 0;
     (void) n1; // expected-error {{unnecessary cast to void [loplugin:casttovoid]}}