[clang] Don't use `VarDecl` of local variables as `ManglingContextDecl` for lambdas (#179035)HEADmain

Currently, in a C++20 modules context, a `VarDecl` of a local variable
can wrongly end up as a `ManglingContextDecl` for a lambda.

Fix this by removing `ContextKind::NonInlineInModulePurview` in
`Sema::getCurrentMangleNumberContext` and add
`IsExternallyVisibleInModulePurview` checks in the appropriate places:

- For externally visible functions defined in a module purview, add a
check to `isInInlineFunction`, renaming it to
`IsInFunctionThatRequiresMangling`
- For externally visible variables defined in a module purview, add a
new `ContextKind::ExternallyVisibleVariableInModulePurview` and an
appropriate check to the `VarDecl` case

Fixes #178893

---------

Co-authored-by: Corentin Jabot <corentinjabot@gmail.com>
Co-authored-by: Chuanqi Xu <yedeng.yd@linux.alibaba.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/test/Modules/pr178893.cppm b/clang/test/Modules/pr178893.cppm
new file mode 100644
index 0000000..e58e183
--- /dev/null
+++ b/clang/test/Modules/pr178893.cppm
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -xc++ -emit-llvm -o - %s -w | FileCheck %s
+
+// CHECK-LABEL: define {{.*}}@_ZZN8PR178893W3mod6format5parseEPiENKUlvE_clEv
+// CHECK-LABEL: define {{.*}}@_ZZN8PR178893W3mod6format5parseEPiENKUlvE0_clEv
+
+export module mod;
+
+namespace PR178893 {
+  struct format {
+      static inline int parse(int* i)
+      {
+          int number;
+          number = [&]() -> int { return i[0]; }();
+
+          volatile bool b = true;
+          if (b) {
+              auto identifier = [&]() -> int { return i[1]; }();
+              return identifier;
+          }
+
+          return number;
+      }
+  };
+
+  int test_format() {
+      int n[2] = {1, 0};
+      return format::parse(n);
+  }
+}