Deduplicate input paths (#20105)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Fixes #20035, fixes #19395

This is for deduplicating input paths to avoid processing the same file
multiple times.

This is my first contribution, so I'm sorry if I miss something. Please
tell me if this is needed for this feature.

## Test Plan

<!-- How was it tested? -->

I just added a test `find_python_files_deduplicated` in
eee1020e32/crates/ruff_workspace/src/resolver.rs (L1017)
. This pull request adds changes to `WalkPythonFilesState::finish`,
which is used in `python_files_in_path`, so they affect some commands
such as `analyze`, `format`, `check` and so on. I will add snapshot
tests for them if necessary.

I’ve already confirmed that the same thing happens with ruff check as
well.

```
$ echo "x   = 1" > example/foo.py
$ uvx ruff check example example/foo.py
I002 [*] Missing required import: `from __future__ import annotations`
--> /path/to/example/foo.py:1:1
help: Insert required import: `from __future__ import annotations`

I002 [*] Missing required import: `from __future__ import annotations`
--> /path/to/example/foo.py:1:1
help: Insert required import: `from __future__ import annotations`

Found 2 errors.
[*] 2 fixable with the `--fix` option.
```

crates/ruff_workspace/src/resolver.rs

@@ -523,10 +523,42 @@ impl<'config> WalkPythonFilesState<'config> {
         let (files, error) = self.merged.into_inner().unwrap();
         error?;
 
-        Ok((files, self.resolver.into_inner().unwrap()))
+        let deduplicated_files = deduplicate_files(files);
+
+        Ok((deduplicated_files, self.resolver.into_inner().unwrap()))
     }
 }
 
+/// Deduplicate files by path, prioritizing `Root` files over `Nested` files.
+///
+/// When the same path appears both as a directly specified input (`Root`)
+/// and via directory traversal (`Nested`), keep the `Root` entry and drop
+/// the `Nested` entry.
+///
+/// Dropping the root entry means that the explicitly passed path may be
+/// unintentionally ignored, since it is treated as nested and can be excluded
+/// despite being requested.
+///
+/// Concretely, with `lint.exclude = ["foo.py"]` and `ruff check . foo.py`,
+/// we must keep `Root(foo.py)` and drop `Nested(foo.py)` so `foo.py` is
+/// linted as the user requested.
+fn deduplicate_files(mut files: ResolvedFiles) -> ResolvedFiles {
+    // Sort by path; for identical paths, prefer Root over Nested; place errors after files
+    files.sort_by(|a, b| match (a, b) {
+        (Ok(a_file), Ok(b_file)) => a_file.cmp(b_file),
+        (Ok(_), Err(_)) => Ordering::Less,
+        (Err(_), Ok(_)) => Ordering::Greater,
+        (Err(_), Err(_)) => Ordering::Equal,
+    });
+
+    files.dedup_by(|a, b| match (a, b) {
+        (Ok(a_file), Ok(b_file)) => a_file.path() == b_file.path(),
+        _ => false,
+    });
+
+    files
+}
+
 struct PythonFilesVisitorBuilder<'s, 'config> {
     state: &'s WalkPythonFilesState<'config>,
     transformer: &'s (dyn ConfigurationTransformer + Sync),
@@ -682,7 +714,7 @@ impl Drop for PythonFilesVisitor<'_, '_> {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq, Ord, PartialOrd)]
 pub enum ResolvedFile {
     /// File explicitly passed to the CLI
     Root(PathBuf),
@@ -715,18 +747,6 @@ impl ResolvedFile {
     }
 }
 
-impl PartialOrd for ResolvedFile {
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-impl Ord for ResolvedFile {
-    fn cmp(&self, other: &Self) -> Ordering {
-        self.path().cmp(other.path())
-    }
-}
-
 /// Return `true` if the Python file at [`Path`] is _not_ excluded.
 pub fn python_file_at_path(
     path: &Path,