feat: let filenames in errors be relative to the current dir if possi…

…ble (#5642)

# Description

## Problem

Resolves #5641

## Summary

It seems `FileMap`'s `name` function was the one that needed that
change.

To avoid doing a syscall to get the current directory every time a name
is needed, `FileMap` gets it at the beginning of the program. I think
this is fine as the current directory can't change while the compilation
is happening.

## Additional Context

None.

## Documentation

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/fm/src/file_map.rs

@@ -34,6 +34,7 @@ impl From<&PathBuf> for PathString {
 pub struct FileMap {
     files: SimpleFiles<PathString, String>,
     name_to_id: HashMap<PathString, FileId>,
+    current_dir: Option<PathBuf>,
 }
 
 // XXX: Note that we derive Default here due to ModuleOrigin requiring us to set a FileId
@@ -82,7 +83,11 @@ impl FileMap {
 }
 impl Default for FileMap {
     fn default() -> Self {
-        FileMap { files: SimpleFiles::new(), name_to_id: HashMap::new() }
+        FileMap {
+            files: SimpleFiles::new(),
+            name_to_id: HashMap::new(),
+            current_dir: std::env::current_dir().ok(),
+        }
     }
 }
 
@@ -92,7 +97,16 @@ impl<'a> Files<'a> for FileMap {
     type Source = &'a str;
 
     fn name(&self, file_id: Self::FileId) -> Result<Self::Name, Error> {
-        Ok(self.files.get(file_id.as_usize())?.name().clone())
+        let name = self.files.get(file_id.as_usize())?.name().clone();
+
+        // See if we can make the file name a bit shorter/easier to read if it starts with the current directory
+        if let Some(current_dir) = &self.current_dir {
+            if let Ok(name_without_prefix) = name.0.strip_prefix(current_dir) {
+                return Ok(PathString::from_path(name_without_prefix.to_path_buf()));
+            }
+        }
+
+        Ok(name)
     }
 
     fn source(&'a self, file_id: Self::FileId) -> Result<Self::Source, Error> {

tooling/lsp/src/requests/mod.rs

@@ -1,3 +1,4 @@
+use std::path::PathBuf;
 use std::{collections::HashMap, future::Future};
 
 use crate::insert_all_files_for_workspace_into_file_manager;
@@ -324,7 +325,12 @@ where
     let file_name = files.name(file_id).ok()?;
 
     let path = file_name.to_string();
-    let uri = Url::from_file_path(path).ok()?;
+
+    // `path` might be a relative path so we canonicalize it to get an absolute path
+    let path_buf = PathBuf::from(path);
+    let path_buf = path_buf.canonicalize().unwrap_or(path_buf);
+
+    let uri = Url::from_file_path(path_buf.to_str()?).ok()?;
 
     Some(Location { uri, range })
 }