[clang]Clang assertion failure after diagnosing missing `promise_type::final_suspend` in coroutine template instantiation

Clang **14.0.0 and later** (assertions enabled) crashes when compiling this code in **C++20 mode or later** (`-std=c++20` or newer).

```cpp
#include

struct Tag {};

struct Y {
bool await_ready() const;
void await_suspend(...) const;
void await_resume() const;
};

struct Promise {
Tag get_return_object();
std::suspend_always initial_suspend();
//std::suspend_always final_suspend() noexcept;
void unhandled_exception();
Y yield_value(int);
void return_void();
};

template
struct std::coroutine_traits {
using promise_type = Promise;
};

template
struct S {
template
static Tag f() { co_yield 0; }
};

Tag g() { return S::f(); }
```
**https://godbolt.org/z/qvjK84f6h**

It first emits the expected diagnostic (`no member named 'final_suspend' in 'Promise'`) for an ill-formed coroutine, but then hits an assertion failure during template instantiation while transforming the coroutine body (`TransformCoyieldExpr`), ending in `LocalInstantiationScope::findInstantiationOf` in `SemaTemplateInstantiate.cpp`. The compiler should diagnose the missing `final_suspend` and recover.

# Output:

```
:28:14: error: no member named 'final_suspend' in 'Promise'
28 | static Tag f() { co_yield 0; }
| ^
clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateInstantiate.cpp:4632: llvm::PointerUnion*>* clang::LocalInstantiationScope::findInstantiationOf(const clang::Decl*): Assertion `isa(D) && "declaration not instantiated in this scope"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20
1. parser at end of file
2. :28:14: instantiating function definition 'S::f'
#0 0x00000000042fea18 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42fea18)
#1 0x00000000042fbe54 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42fbe54)
#2 0x000000000423e748 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x00007fe4ae642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x00007fe4ae6969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x00007fe4ae642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x00007fe4ae6287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x00007fe4ae62871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x00007fe4ae639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x000000000758598d clang::LocalInstantiationScope::findInstantiationOf(clang::Decl const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x758598d)
#10 0x000000000766d017 clang::Sema::FindInstantiatedDecl(clang::SourceLocation, clang::NamedDecl*, clang::MultiLevelTemplateArgumentList const&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x766d017)
#11 0x00000000075ac9f3 (anonymous namespace)::TemplateInstantiator::TransformDecl(clang::SourceLocation, clang::Decl*) SemaTemplateInstantiate.cpp:0:0
#12 0x00000000075c2190 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformDeclRefExpr(clang::DeclRefExpr*) SemaTemplateInstantiate.cpp:0:0
#13 0x00000000075c269b (anonymous namespace)::TemplateInstantiator::TransformDeclRefExpr(clang::DeclRefExpr*) SemaTemplateInstantiate.cpp:0:0
#14 0x0000000007592283 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#15 0x00000000075c14e0 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformMemberExpr(clang::MemberExpr*) SemaTemplateInstantiate.cpp:0:0
#16 0x00000000075923c7 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#17 0x00000000075b53d6 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#18 0x000000000759217c clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#19 0x00000000075b1f15 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformInitializer(clang::Expr*, bool) (.part.0) SemaTemplateInstantiate.cpp:0:0
#20 0x00000000075b257c clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCoyieldExpr(clang::CoyieldExpr*) SemaTemplateInstantiate.cpp:0:0
#21 0x000000000759226b clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#22 0x00000000075922f0 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#23 0x00000000075cf3b7 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformStmt(clang::Stmt*, clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::StmtDiscardKind) SemaTemplateInstantiate.cpp:0:0
#24 0x00000000075cfa65 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#25 0x00000000075d8e9d clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75d8e9d)
#26 0x00000000076751d0 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x76751d0)
#27 0x0000000007672d96 clang::Sema::PerformPendingInstantiations(bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7672d96)
#28 0x0000000006bee482 clang::Sema::ActOnEndOfTranslationUnitFragment(clang::TUFragmentKind) (.part.0) Sema.cpp:0:0
#29 0x0000000006bee802 clang::Sema::ActOnEndOfTranslationUnit() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6bee802)
#30 0x0000000006a597d5 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a597d5)
#31 0x0000000006a3a78a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a3a78a)
#32 0x0000000004c66488 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c66488)
#33 0x0000000004f60135 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f60135)
#34 0x0000000004edff0e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4edff0e)
#35 0x000000000505a7cd clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x505a7cd)
#36 0x0000000000dce92e cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdce92e)
#37 0x0000000000dc52fa ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#38 0x0000000000dc547d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#39 0x0000000004cd96e9 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#40 0x000000000423ebe4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x423ebe4)
#41 0x0000000004cd9cff clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#42 0x0000000004c9a692 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c9a692)
#43 0x0000000004c9b63e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c9b63e)
#44 0x0000000004ca2a95 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ca2a95)
#45 0x0000000000dcaca1 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdcaca1)
#46 0x0000000000c88434 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc88434)
#47 0x00007fe4ae629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#48 0x00007fe4ae629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#49 0x0000000000dc4d95 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdc4d95)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```

Start by reproducing the reduced C++20 example from the issue with an assertions-enabled Clang build. Read SemaTemplateInstantiate.cpp around TransformCoyieldExpr and LocalInstantiationScope::findInstantiationOf, then trace how the missing final_suspend diagnostic is handled during template instantiation. Done means the diagnostic is emitted without an assertion or compiler crash.

Written by the indexing model from the issue text.