[AST] Add mechanism to notify module loading to other clients

[medismailben]

This patch adds an optional callback function member to the AST Context.
The callback gets invoked when a new module (or overlay module) gets
loaded.

This can be used for instance by other clients, such as lldb, to perform
actions when a module gets loaded, like showing progress to the end-user.

rdar://94165195

Signed-off-by: Med Ismail Bennani [email protected]

[JDevlieghere]

Did you consider making the callback a member of the ASTContext? Do the functions take different callbacks? I'm curious because that would require only adding a function + a member instead of changing 6 existing function signatures.

[adrian-prantl]

All in all I'm not sure I like this version of the patch. If (most) dependencies are loaded through ASTContext, then we should only need to modify loadModule() since that's called by all the other functions eventually.
My idea from yesterday for letting the module loaders customize the message doesn't actually work, because we can't know ahead of time whether the import is going to succeed. So the best thing we can do is printing the name of the module and the fact that we're importing it.

[adrian-prantl]

It would be useful if we had a way of communicating the compilation of Clang module dependencies of Clang modules, because that is very slow, but IIUC, not even ClangImporter know about this as it's handled by Clang? We could try building with -Rmodule-build and listening to the Diagnostics, but let's not make the perfect the enemy of the good. Even just printing the toplevel imports is better than nothing.

[medismailben]

Addressed @JDevlieghere & @adrian-prantl feedbacks

[medismailben]

@swift-ci test

[medismailben]

@swift-ci test

[nkcsgexi]

Reasonable change with a minor comment.

[medismailben]

@swift-ci test

[medismailben]

Cherry-picked to main in #59466