Allow cargo-fmt to handle formatting individual files.

Adds an additional command line option ``--src-file`` / ``-s``

It should be noted that this does not allow cargo-fmt to format an
arbitrary rust file. The file must be contained with a target specified
in a Cargo.toml file.

Adjustments were also made to prevent cargo-fmt from passing along
certain arguments to rustfmt. For example, users can no longer pass rust
files to rustfmt through cargo-fmt. Additionally, users cannot pass
--edition to cargo-fmt, since editions are read from the Cargo.toml.

Tests were added in ``src/cargo-fmt/test/mod.rs`` and integration tests
were added to ``tests/cargo-fmt/main.rs``

Author: ytmimi

src/cargo-fmt/main.rs

@@ -49,6 +49,10 @@ pub struct Opts {
     )]
     packages: Vec<String>,
 
+    /// Specify a source file to format
+    #[clap(short = 's', long = "src-file", value_name = "src-file")]
+    src_file: Option<PathBuf>,
+
     /// Specify path to Cargo.toml
     #[clap(long = "manifest-path", value_name = "manifest-path")]
     manifest_path: Option<String>,
@@ -94,6 +98,28 @@ fn execute() -> i32 {
 
     let opts = Opts::parse_from(args);
 
+    if opts.src_file.is_some() & !opts.packages.is_empty() {
+        print_usage_to_stderr("cannot format source files and packages at the same time");
+        return FAILURE;
+    }
+
+    if opts.src_file.is_some() & opts.format_all {
+        print_usage_to_stderr("cannot format all packages when specifying source files");
+        return FAILURE;
+    }
+
+    if opts.rustfmt_options.iter().any(|s| s.ends_with(".rs")) {
+        print_usage_to_stderr(
+            "cannot pass rust files to rustfmt through cargo-fmt. Use '--src-file' instead",
+        );
+        return FAILURE;
+    }
+
+    if opts.rustfmt_options.iter().any(|s| s.contains("--edition")) {
+        print_usage_to_stderr("cannot pass '--edition' to rustfmt through cargo-fmt");
+        return FAILURE;
+    }
+
     let verbosity = match (opts.verbose, opts.quiet) {
         (false, false) => Verbosity::Normal,
         (false, true) => Verbosity::Quiet,
@@ -319,17 +345,23 @@ pub enum CargoFmtStrategy {
     /// Format every packages and dependencies.
     All,
     /// Format packages that are specified by the command line argument.
-    Some(Vec<String>),
+    Packages(Vec<String>),
     /// Format the root packages only.
     Root,
+    /// Format individual source files specified by the command line arguments.
+    SourceFile(PathBuf),
 }
 
 impl CargoFmtStrategy {
     pub fn from_opts(opts: &Opts) -> CargoFmtStrategy {
+        if let Some(ref src_file) = opts.src_file {
+            return CargoFmtStrategy::SourceFile(src_file.clone());
+        }
+
         match (opts.format_all, opts.packages.is_empty()) {
             (false, true) => CargoFmtStrategy::Root,
             (true, _) => CargoFmtStrategy::All,
-            (false, false) => CargoFmtStrategy::Some(opts.packages.clone()),
+            (false, false) => CargoFmtStrategy::Packages(opts.packages.clone()),
         }
     }
 }
@@ -346,9 +378,12 @@ fn get_targets(
         CargoFmtStrategy::All => {
             get_targets_recursive(manifest_path, &mut targets, &mut BTreeSet::new())?
         }
-        CargoFmtStrategy::Some(ref hitlist) => {
+        CargoFmtStrategy::Packages(ref hitlist) => {
             get_targets_with_hitlist(manifest_path, hitlist, &mut targets)?
         }
+        CargoFmtStrategy::SourceFile(ref src_file) => {
+            get_target_from_src_file(manifest_path, &src_file, &mut targets)?
+        }
     }
 
     if targets.is_empty() {
@@ -361,6 +396,57 @@ fn get_targets(
     }
 }
 
+fn get_target_from_src_file(
+    manifest_path: Option<&Path>,
+    src_file: &PathBuf,
+    targets: &mut BTreeSet<Target>,
+) -> Result<(), io::Error> {
+    let metadata = get_cargo_metadata(manifest_path)?;
+
+    let get_target = |src_path: &Path| {
+        metadata
+            .packages
+            .iter()
+            .map(|p| p.targets.iter())
+            .flatten()
+            .filter(|t| {
+                let kind = &t.kind[0];
+                // to prevent formatting any arbitrary file within the root of our
+                // project we special case the build.rs script, becuase it's parent
+                // is the root of the project and we would always select the custom-build
+                // target in the event that we couldn't find a better target to associate
+                // with our file.
+                if kind == "custom-build" && !src_path.ends_with("build.rs") {
+                    return false;
+                }
+
+                if let Ok(target_path) = fs::canonicalize(&t.src_path) {
+                    let target_dir = target_path
+                        .parent()
+                        .expect("Target src_path should have a parent directory");
+                    src_path.starts_with(target_dir)
+                } else {
+                    false
+                }
+            })
+            .max_by(|t1, t2| {
+                let t1_len = t1.src_path.components().count();
+                let t2_len = t2.src_path.components().count();
+                t1_len.cmp(&t2_len)
+            })
+    };
+
+    let canonicalize = fs::canonicalize(&src_file)?;
+    if let Some(target) = get_target(&canonicalize) {
+        targets.insert(Target {
+            path: src_file.to_owned(),
+            kind: target.kind[0].clone(),
+            edition: target.edition.clone(),
+        });
+    }
+    Ok(())
+}
+
 fn get_targets_root_only(
     manifest_path: Option<&Path>,
     targets: &mut BTreeSet<Target>,

src/cargo-fmt/test/mod.rs

@@ -1,4 +1,5 @@
 use super::*;
+use std::path::PathBuf;
 
 mod message_format;
 mod targets;
@@ -16,6 +17,7 @@ fn default_options() {
     assert_eq!(false, o.format_all);
     assert_eq!(None, o.manifest_path);
     assert_eq!(None, o.message_format);
+    assert_eq!(None, o.src_file);
 }
 
 #[test]
@@ -27,6 +29,8 @@ fn good_options() {
         "p1",
         "-p",
         "p2",
+        "-s",
+        "file.rs",
         "--message-format",
         "short",
         "--check",
@@ -39,6 +43,7 @@ fn good_options() {
     assert_eq!(false, o.version);
     assert_eq!(true, o.check);
     assert_eq!(vec!["p1", "p2"], o.packages);
+    assert_eq!(Some(PathBuf::from("file.rs")), o.src_file);
     assert_eq!(vec!["--edition", "2018"], o.rustfmt_options);
     assert_eq!(false, o.format_all);
     assert_eq!(Some(String::from("short")), o.message_format);
@@ -90,6 +95,25 @@ fn multiple_packages_one_by_one() {
     assert_eq!(3, o.packages.len());
 }
 
+#[test]
+fn cant_list_more_than_one_source_file() {
+    assert!(
+        Opts::command()
+            .try_get_matches_from(&["test", "-s", "src/a.rs", "--src-file", "src/b.rs"])
+            .is_err()
+    );
+    assert!(
+        !Opts::command()
+            .try_get_matches_from(&["test", "-s", "src/a.rs"])
+            .is_err()
+    );
+    assert!(
+        !Opts::command()
+            .try_get_matches_from(&["test", "--src-file", "src/b.rs"])
+            .is_err()
+    );
+}
+
 #[test]
 fn multiple_packages_grouped() {
     let o = Opts::parse_from(&[
@@ -139,3 +163,39 @@ fn empty_packages_4() {
             .is_err()
     );
 }
+
+#[test]
+fn empty_source_files_1() {
+    assert!(
+        Opts::command()
+            .try_get_matches_from(&["test", "-s"])
+            .is_err()
+    );
+}
+
+#[test]
+fn empty_source_files_2() {
+    assert!(
+        Opts::command()
+            .try_get_matches_from(&["test", "-s", "--", "--check"])
+            .is_err()
+    );
+}
+
+#[test]
+fn empty_source_files_3() {
+    assert!(
+        Opts::command()
+            .try_get_matches_from(&["test", "-s", "--verbose"])
+            .is_err()
+    );
+}
+
+#[test]
+fn empty_source_files_4() {
+    assert!(
+        Opts::command()
+            .try_get_matches_from(&["test", "-s", "--check"])
+            .is_err()
+    );
+}

tests/cargo-fmt/main.rs

@@ -96,3 +96,42 @@ fn cargo_fmt_out_of_line_test_modules() {
         assert!(stdout.contains(&format!("Diff in {}", path.display())))
     }
 }
+
+#[test]
+fn cannot_pass_rust_files_to_rustfmt_through_caro_fmt() {
+    let (_, stderr) = cargo_fmt(&["--", "src/main.rs"]);
+    assert!(stderr.starts_with(
+        "cannot pass rust files to rustfmt through cargo-fmt. Use '--src-file' instead"
+    ))
+}
+
+#[test]
+fn cannot_pass_edition_to_rustfmt_through_caro_fmt() {
+    let (_, stderr) = cargo_fmt(&["--", "--edition", "2021"]);
+    assert!(stderr.starts_with("cannot pass '--edition' to rustfmt through cargo-fmt"))
+}
+
+#[test]
+fn specify_source_files_when_running_cargo_fmt() {
+    let path = "tests/cargo-fmt/source/workspaces/path-dep-above/e/src/main.rs";
+    // test that we can run cargo-fmt on a single src file
+    assert_that!(&["-v", "--check", "-s", path], contains(path));
+}
+
+#[test]
+fn specify_source_files_in_a_workspace_when_running_cargo_fmt() {
+    let path = "tests/cargo-fmt/source/workspaces/path-dep-above/ws/a/src/main.rs";
+    assert_that!(&["-v", "--check", "-s", path], contains(path));
+}
+
+#[test]
+fn formatting_source_files_and_packages_at_the_same_time_is_not_supported() {
+    let (_, stderr) = cargo_fmt(&["--check", "-s", "src/main.rs", "-p", "p1"]);
+    assert!(stderr.starts_with("cannot format source files and packages at the same time"))
+}
+
+#[test]
+fn formatting_source_files_and_using_package_related_arguments_is_not_supported() {
+    let (_, stderr) = cargo_fmt(&["--check", "--all", "-s", "src/main.rs"]);
+    assert!(stderr.starts_with("cannot format all packages when specifying source files"))
+}