Simplify Module.read and its interaction with FileManager

[Geod24]

Since the FileManager will read a file if it exists on the filesystem,
the else clause of Module.read was only ever called if File.read would fail.
As a result, the code can be simplified, and loadSourceBuffer can be renamed
to match its true purpose (printing a decent error message on missing file).

[dlang-bot]

Thanks for your pull request, @Geod24!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✗	17167	blocker	dmd fails to write to file or create directory with more than 248 characters in the path

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#13828"

[thewilsonator]

compilable\issue17167.sh seems to fail everywhere on Azure

[Geod24]

Yep, legit failure, looking into it.

[ibuclaw]

Check headers, modules.h, file.h, etc. For declarations that should be removed.

[Geod24]

@ibuclaw : FileBuffer is still a member of class Module so it can't be removed yet.
frontend.h removes it because its decl is no longer used. A future PR will remove it as a member of Module (I'm basically trying to get rid of the coupling between module and IO).

[Geod24]

Found (and fixed) the bug

[Geod24]

To answer @ibuclaw more precisely:

% grep -nR -e "struct File$" -e "struct FileBuffer" $(find src -name "*.h")
src/dmd/frontend.h:232:struct FileBuffer;
src/dmd/root/file.h:15:struct FileBuffer
src/dmd/root/file.h:25:struct File
src/dmd/module.h:17:struct FileBuffer;

I could remove root/file.h if you guys are not using it, but perhaps it's better to wait until it's not used as a member of an AST node ? :)

[ibuclaw]

To answer @ibuclaw more precisely:

% grep -nR -e "struct File$" -e "struct FileBuffer" $(find src -name "*.h")
src/dmd/frontend.h:232:struct FileBuffer;
src/dmd/root/file.h:15:struct FileBuffer
src/dmd/root/file.h:25:struct File
src/dmd/module.h:17:struct FileBuffer;

I could remove root/file.h if you guys are not using it, but perhaps it's better to wait until it's not used as a member of an AST node ? :)

It could be a void* field. Having a quick scan, the C++ driver still needs to set srcBuffer->data when creating a module for code read from stdin. If there was a C++ helper method such as Module::setSrcBuffer(char *ptr, size_t length) then you could internalize File and FileBuffer, removing file.h outright.

Just making sure that the C++ interface has been checked against for the removals here.

Headers have been checked.