[modules] Repro for pure virtual base class method crash

[andrewjcg]

Summary

Somewhat simplified repro case for crash when using clang modules.

Output: P8228

clang/test/Modules/Inputs/set-pure-crash/a.h

+#pragma once
+
+struct Tag {};
+
+template <typename T>
+class Base {
+public:
+  virtual void func() = 0;
+};
+
+Base<Tag> bar();

clang/test/Modules/Inputs/set-pure-crash/b.h

+#pragma once
+
+#include "a.h"
+#include "c.h"
+
+template <typename Fun, typename = func<Fun>>
+void foo(Fun) {}
+
+class Child : public Base<Tag> {
+public:
+  void func() {
+    foo([]() {});
+  }
+};

clang/test/Modules/Inputs/set-pure-crash/c.h

+#pragma once
+
+template <typename>
+struct func {
+};

clang/test/Modules/Inputs/set-pure-crash/module.modulemap

+module a {
+  header "a.h"
+}
+
+module b {
+  header "b.h"
+}
+
+module c {
+  header "c.h"
+}

clang/test/Modules/set-pure-crash.cpp

+// RUN: rm -rf %t
+// RUN: %clang_cc1 -O0 -emit-llvm -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I %S/Inputs/set-pure-crash -verify %s -o %t
+
+// expected-no-diagnostics
+
+#include "b.h"
+#include "c.h"
+
+auto t = func<const char *>();