ilya-biryukov wrote:
Here's a reproducer for our breakage:
```cpp
// RUN: rm -rf %t
// RUN: split-file %s %t
//
// First, build a module with a header.
//
// RUN: %clang_cc1 -fmodules -fmodule-map-file=%t/modules1.map -fmodule-name=a
-emit-module -xc++ -fmodules-embed-all-files -o %t/a.pcm %t/modules1.map
// RUN: %clang_cc1 -fmodules -fmodule-map-file=%t/modules1.map
-fmodule-map-file=%t/modules2.map -fmodule-name=b -emit-module \
// RUN: -fmodule-file=%t/a.pcm -xc++ -fmodules-embed-all-files -o %t/b.pcm
%t/modules2.map
//
// Remove the header and check we can still build the code that finds it in a
PCM.
//
// RUN: rm %t/foo.h
// RUN: %clang_cc1 -fmodules -fmodule-map-file=%t/modules2.map
-fmodule-file=%t/b.pcm -fsyntax-only %t/use.cpp
//--- modules1.map
module a {
module foo {
header "foo.h"
export *
}
export *
}
//--- modules2.map
module all_textual {
module foo {
textual header "foo.h"
export *
}
module wrap_foo {
textual header "wrap_foo.h"
export *
}
export *
}
module b {
module wrap_foo {
private header "wrap_foo.h"
export *
}
export *
}
//--- foo.h
#ifndef FOO_H
#define FOO_H
void foo();
#endif
//--- wrap_foo.h
#include "foo.h"
//--- use.cpp
#include "wrap_foo.h"
void test() {
foo();
}
```
It previously built fine because the `all_textual.foo` and its parent module
used to be marked as unavailable because `foo.h` could not be found here:
https://github.com/llvm/llvm-project/blob/09fd8f0093b8ff489d76285d893be152e4ca4c24/clang/lib/Lex/ModuleMap.cpp#L326
and therefore it made us pick the module `b.wrap_foo` later when resolving
`wrap_foo.h` instead of `all_textual.wrap_foo` based on the code here:
https://github.com/llvm/llvm-project/blob/09fd8f0093b8ff489d76285d893be152e4ca4c24/clang/lib/Lex/ModuleMap.cpp#L618
After the change, we no longer mark `all_textual` as unavailable and pick
`all_textual.wrap_foo`, which causes us to reprocess the header.
I know what we do is cheesy and we might need to reconsider how to approach it,
but this is a breaking change and it would be great to find a resolution for it
before committing to the new behavior. Could we revert this while we discuss
the potential ways out of it?
https://github.com/llvm/llvm-project/pull/138227
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