Remove FixMode::None (#5087)

## Summary

We now _always_ generate fixes, so `FixMode::None` and
`FixMode::Generate` are redundant. We can also remove the TODO around
`--fix-dry-run`, since that's our default behavior.

Closes #5081.

crates/ruff/src/settings/flags.rs

@@ -1,19 +1,8 @@
-#[derive(Debug, Copy, Clone, Hash)]
+#[derive(Debug, Copy, Clone, Hash, is_macro::Is)]
 pub enum FixMode {
     Generate,
     Apply,
     Diff,
-    None,
-}
-
-impl From<bool> for FixMode {
-    fn from(value: bool) -> Self {
-        if value {
-            Self::Apply
-        } else {
-            Self::None
-        }
-    }
 }
 
 #[derive(Debug, Copy, Clone, Hash, result_like::BoolLike)]

crates/ruff_cli/src/commands/run.rs

@@ -247,21 +247,21 @@ mod test {
             &overrides,
             Cache::Disabled,
             Noqa::Enabled,
-            FixMode::None,
+            FixMode::Generate,
         )?;
 
         let printer = Printer::new(
             SerializationFormat::Text,
             LogLevel::Default,
-            FixMode::None,
+            FixMode::Generate,
             Flags::SHOW_VIOLATIONS,
         );
         let mut writer: Vec<u8> = Vec::new();
-        // Mute the terminal color codes
+        // Mute the terminal color codes.
         colored::control::set_override(false);
         printer.write_once(&diagnostics, &mut writer)?;
         // TODO(konstin): Set jupyter notebooks as none-fixable for now
-        // TODO(konstin) 2: Make jupyter notebooks fixable
+        // TODO(konstin): Make jupyter notebooks fixable
         let expected = format!(
             "{valid_ipynb}:cell 1:2:5: F841 [*] Local variable `x` is assigned to but never used
 {valid_ipynb}:cell 3:1:24: B006 Do not use mutable data structures for argument defaults

crates/ruff_cli/src/diagnostics.rs

@@ -110,10 +110,7 @@ pub(crate) fn lint_path(
     // to cache `fixer::Mode::Apply`, since a file either has no fixes, or we'll
     // write the fixes to disk, thus invalidating the cache. But it's a bit hard
     // to reason about. We need to come up with a better solution here.)
-    let metadata = if cache.into()
-        && noqa.into()
-        && matches!(autofix, flags::FixMode::None | flags::FixMode::Generate)
-    {
+    let metadata = if cache.into() && noqa.into() && autofix.is_generate() {
         let metadata = path.metadata()?;
         if let Some((messages, imports)) = cache::get(path, package, &metadata, settings) {
             debug!("Cache hit for: {}", path.display());
@@ -170,23 +167,25 @@ pub(crate) fn lint_path(
             &mut source_kind,
         ) {
             if !fixed.is_empty() {
-                if matches!(autofix, flags::FixMode::Apply) {
-                    match &source_kind {
+                match autofix {
+                    flags::FixMode::Apply => match &source_kind {
                         SourceKind::Python(_) => {
                             write(path, transformed.as_bytes())?;
                         }
                         SourceKind::Jupyter(notebook) => {
                             notebook.write(path)?;
                         }
+                    },
+                    flags::FixMode::Diff => {
+                        let mut stdout = io::stdout().lock();
+                        TextDiff::from_lines(contents.as_str(), &transformed)
+                            .unified_diff()
+                            .header(&fs::relativize_path(path), &fs::relativize_path(path))
+                            .to_writer(&mut stdout)?;
+                        stdout.write_all(b"\n")?;
+                        stdout.flush()?;
                     }
-                } else if matches!(autofix, flags::FixMode::Diff) {
-                    let mut stdout = io::stdout().lock();
-                    TextDiff::from_lines(contents.as_str(), &transformed)
-                        .unified_diff()
-                        .header(&fs::relativize_path(path), &fs::relativize_path(path))
-                        .to_writer(&mut stdout)?;
-                    stdout.write_all(b"\n")?;
-                    stdout.flush()?;
+                    flags::FixMode::Generate => {}
                 }
             }
             (result, fixed)
@@ -269,23 +268,28 @@ pub(crate) fn lint_stdin(
             settings,
             &mut source_kind,
         ) {
-            if matches!(autofix, flags::FixMode::Apply) {
-                // Write the contents to stdout, regardless of whether any errors were fixed.
-                io::stdout().write_all(transformed.as_bytes())?;
-            } else if matches!(autofix, flags::FixMode::Diff) {
-                // But only write a diff if it's non-empty.
-                if !fixed.is_empty() {
-                    let text_diff = TextDiff::from_lines(contents, &transformed);
-                    let mut unified_diff = text_diff.unified_diff();
-                    if let Some(path) = path {
-                        unified_diff.header(&fs::relativize_path(path), &fs::relativize_path(path));
-                    }
-
-                    let mut stdout = io::stdout().lock();
-                    unified_diff.to_writer(&mut stdout)?;
-                    stdout.write_all(b"\n")?;
-                    stdout.flush()?;
+            match autofix {
+                flags::FixMode::Apply => {
+                    // Write the contents to stdout, regardless of whether any errors were fixed.
+                    io::stdout().write_all(transformed.as_bytes())?;
                 }
+                flags::FixMode::Diff => {
+                    // But only write a diff if it's non-empty.
+                    if !fixed.is_empty() {
+                        let text_diff = TextDiff::from_lines(contents, &transformed);
+                        let mut unified_diff = text_diff.unified_diff();
+                        if let Some(path) = path {
+                            unified_diff
+                                .header(&fs::relativize_path(path), &fs::relativize_path(path));
+                        }
+
+                        let mut stdout = io::stdout().lock();
+                        unified_diff.to_writer(&mut stdout)?;
+                        stdout.write_all(b"\n")?;
+                        stdout.flush()?;
+                    }
+                }
+                flags::FixMode::Generate => {}
             }
 
             (result, fixed)
@@ -301,7 +305,7 @@ pub(crate) fn lint_stdin(
             let fixed = FxHashMap::default();
 
             // Write the contents to stdout anyway.
-            if matches!(autofix, flags::FixMode::Apply) {
+            if autofix.is_apply() {
                 io::stdout().write_all(contents.as_bytes())?;
             }
 

crates/ruff_cli/src/lib.rs

@@ -192,23 +192,17 @@ fn check(args: CheckArgs, log_level: LogLevel) -> Result<ExitStatus> {
     } = pyproject_config.settings.cli;
 
     // Autofix rules are as follows:
+    // - By default, generate all fixes, but don't apply them to the filesystem.
     // - If `--fix` or `--fix-only` is set, always apply fixes to the filesystem (or
     //   print them to stdout, if we're reading from stdin).
-    // - Otherwise, if `--format json` is set, generate the fixes (so we print them
-    //   out as part of the JSON payload), but don't write them to disk.
     // - If `--diff` or `--fix-only` are set, don't print any violations (only
     //   fixes).
-    // TODO(charlie): Consider adding ESLint's `--fix-dry-run`, which would generate
-    // but not apply fixes. That would allow us to avoid special-casing JSON
-    // here.
     let autofix = if cli.diff {
         flags::FixMode::Diff
     } else if fix || fix_only {
         flags::FixMode::Apply
-    } else if matches!(format, SerializationFormat::Json) {
-        flags::FixMode::Generate
     } else {
-        flags::FixMode::None
+        flags::FixMode::Generate
     };
     let cache = !cli.no_cache;
     let noqa = !cli.ignore_noqa;
@@ -238,7 +232,7 @@ fn check(args: CheckArgs, log_level: LogLevel) -> Result<ExitStatus> {
     }
 
     if cli.add_noqa {
-        if !matches!(autofix, flags::FixMode::None) {
+        if !autofix.is_generate() {
             warn_user_once!("--fix is incompatible with --add-noqa.");
         }
         let modifications =

crates/ruff_cli/src/printer.rs

@@ -141,9 +141,9 @@ impl Printer {
                     .sum::<usize>();
                 if fixed > 0 {
                     let s = if fixed == 1 { "" } else { "s" };
-                    if matches!(self.autofix_level, flags::FixMode::Apply) {
+                    if self.autofix_level.is_apply() {
                         writeln!(stdout, "Fixed {fixed} error{s}.")?;
-                    } else if matches!(self.autofix_level, flags::FixMode::Diff) {
+                    } else {
                         writeln!(stdout, "Would fix {fixed} error{s}.")?;
                     }
                 }
@@ -391,7 +391,7 @@ const fn show_fix_status(autofix_level: flags::FixMode) -> bool {
     // this pass! (We're occasionally unable to determine whether a specific
     // violation is fixable without trying to fix it, so if autofix is not
     // enabled, we may inadvertently indicate that a rule is fixable.)
-    !matches!(autofix_level, flags::FixMode::Apply)
+    !autofix_level.is_apply()
 }
 
 fn print_fix_summary<T: Write>(stdout: &mut T, fixed: &FxHashMap<String, FixTable>) -> Result<()> {