[clang][Interp] Reject static lambdas with captures

[tbaederr]

Static lambdas cannot have captures. They may still end up in the constant evaluator though. They've been diagnosted appropriately before, so just reject them here.

This is similar to #74661, but for the new constant expression interpreter.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

Changes

A version of #74661 for the new interpreter. It didn't crash before, but we did emit a few non-sensical diagnostics.

---

Full diff: https://github.com/llvm/llvm-project/pull/74718.diff

2 Files Affected:

• (modified) clang/lib/AST/Interp/ByteCodeEmitter.cpp (+5)
• (modified) clang/test/AST/Interp/cxx23.cpp (+24-3)

diff --git a/clang/lib/AST/Interp/ByteCodeEmitter.cpp b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
index 89b7708c0c2a1..045263447cbc9 100644
--- a/clang/lib/AST/Interp/ByteCodeEmitter.cpp
+++ b/clang/lib/AST/Interp/ByteCodeEmitter.cpp
@@ -61,6 +61,11 @@ ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl) {
       MD->getParent()->getCaptureFields(LC, LTC);
 
       for (auto Cap : LC) {
+        // Static lambdas cannot have any captures. If this one does,
+        // it has already been diagnosed and we can only ignore it.
+        if (MD->isStatic())
+          return nullptr;
+
         unsigned Offset = R->getField(Cap.second)->Offset;
         this->LambdaCaptures[Cap.first] = {
             Offset, Cap.second->getType()->isReferenceType()};
diff --git a/clang/test/AST/Interp/cxx23.cpp b/clang/test/AST/Interp/cxx23.cpp
index e284a66626fb3..bd1cf186d519c 100644
--- a/clang/test/AST/Interp/cxx23.cpp
+++ b/clang/test/AST/Interp/cxx23.cpp
@@ -4,9 +4,6 @@
 // RUN: %clang_cc1 -std=c++23 -fsyntax-only -fcxx-exceptions -verify=expected23 %s -fexperimental-new-constant-interpreter
 
 
-// expected23-no-diagnostics
-
-
 /// FIXME: The new interpreter is missing all the 'control flows through...' diagnostics.
 
 constexpr int f(int n) {  // ref20-error {{constexpr function never produces a constant expression}} \
@@ -82,3 +79,27 @@ constexpr int k(int n) {
   return m;
 }
 constexpr int k0 = k(0);
+
+namespace StaticLambdas {
+  constexpr auto static_capture_constexpr() {
+    char n = 'n';
+    return [n] static { return n; }(); // expected23-error {{a static lambda cannot have any captures}} \
+                                       // expected20-error {{a static lambda cannot have any captures}} \
+                                       // expected20-warning {{are a C++23 extension}} \
+                                       // expected20-warning {{is a C++23 extension}} \
+                                       // ref23-error {{a static lambda cannot have any captures}} \
+                                       // ref20-error {{a static lambda cannot have any captures}} \
+                                       // ref20-warning {{are a C++23 extension}} \
+                                       // ref20-warning {{is a C++23 extension}}
+  }
+  static_assert(static_capture_constexpr()); // expected23-error {{static assertion expression is not an integral constant expression}} \
+                                             // expected20-error {{static assertion expression is not an integral constant expression}} \
+                                             // ref23-error {{static assertion expression is not an integral constant expression}} \
+                                             // ref20-error {{static assertion expression is not an integral constant expression}}
+
+  constexpr auto capture_constexpr() {
+    char n = 'n';
+    return [n] { return n; }();
+  }
+  static_assert(capture_constexpr());
+}

[shafik]

Can you please add more details to the description so folks reading the git log know what the change is without having to do more digging.

[puremourning]

Lgtm

[puremourning]

Not sure we need to even enter this loop.