[PATCH] D51159: [FileManager] Do not call 'real_path' in getFile().

[Eric Liu via Phabricator via cfe-commits]

ioeric added inline comments.


================
Comment at: lib/Basic/FileManager.cpp:319
 
-  SmallString<128> RealPathName;
-  if (!FS->getRealPath(InterndFileName, RealPathName))
-    UFE.RealPathName = RealPathName.str();
+  if (UFE.File) {
+    if (auto Path = UFE.File->getName()) {
----------------
simark wrote:
> ioeric wrote:
> > simark wrote:
> > > ioeric wrote:
> > > > simark wrote:
> > > > > What's the rationale for only computing the field if `UFE.File` is non-null?
> > > > > 
> > > > > Previously, if you looked up the file with `openFile == false` and then later `openFile == true`, the `RealPathName` field would not be set because of this.  That doesn't seem right.
> > > > There has been no guarantee that RealFilePath is always set. I think that's the reason why the acceasor is called tryGetRealPathName.
> > > The way I understood it was that it could be empty because computing the real path can fail.  Not just because we didn't skipped computing it.
> > I agree that the API is confusing and lack of documentation (and we should fix), but the previous implementation did skip the computation if File is not available though. 
> > I agree that the API is confusing and lack of documentation (and we should fix), but the previous implementation did skip the computation if File is not available though.
> 
> Did it have a reason not to?  What is the `RealPathName` field useful for, if it's unreliable?
I think the biggest concern is the performance.
 
For example, clangd code completion latency increased dramatically with `real_path`:
With `real_path`:
{F7039629}
{F7041680}

Wihtou `real_path`:
{F7039630}


================
Comment at: lib/Basic/FileManager.cpp:326
+      llvm::sys::path::remove_dots(AbsPath, /*remove_dot_dot=*/true);
+      UFE.RealPathName = AbsPath.str();
+    }
----------------
simark wrote:
> ioeric wrote:
> > simark wrote:
> > > ioeric wrote:
> > > > simark wrote:
> > > > > If the path contains symlinks, doesn't this put a non-real path in the RealPathName field?  Won't users (e.g. clangd) use this value thinking it is a real path, when it is actually not?
> > > > This was the original behavior. In general, File Manager should never call real_path for users because it can be very expensive. Users should call real_path if they want to resolve symlinks. That said, it's fair to say that "RealPathName" is just a wrong name, and we should clean it up at some point.
> > > Ok, then if the goal is not to actually have a real path (in the realpath(3) sense), that's fine.  But I think we should rename the field sooner than later, it's really confusing.
> > > 
> > > That also means that it's kind of useless for us in clangd, so we should always call real_path there and not rely on that field.
> > > Ok, then if the goal is not to actually have a real path (in the realpath(3) sense), that's fine. But I think we should rename the field sooner than later, it's really confusing.
> > +1
> > 
> > > That also means that it's kind of useless for us in clangd, so we should always call real_path there and not rely on that field.
> > I guess it depends on whether you want symlink resolution or not. I know that clangd's index symbol collector resolves symlink explicitly, but I don't think clangd enforces symlink resolution in general?
> > I guess it depends on whether you want symlink resolution or not. I know that clangd's index symbol collector resolves symlink explicitly, but I don't think clangd enforces symlink resolution in general?
> 
> If we don't, we probably risk having duplicate results similar to what
> 
>   https://reviews.llvm.org/D48687
> 
> fixed, by with paths differing because of symlinks instead of dot-dots.
Was the bug addressed in D48687 actually caused by symlinks though? If want we want is absolute paths with dotdot cleaned, it should be much cheaper to call `VFS::makeAbsolutePath` with `remove_dot_dot`.

In general, it's unclear whether clangd should resolve symlink (it might not always be what users want), and it should probably be a decision made by the build system integration. I think we would need a much more careful design if we decide to handle symlinks in clangd. 


Repository:
  rC Clang

https://reviews.llvm.org/D51159