Only show warnings for empty preview selectors when enabling rules (#7842)

Closes #7491

Users found it confusing that warnings were displayed when ignoring a
preview rule (which has no effect without `--preview`). While we could
retain the warning with different messaging, I've opted to remove it for
now. With this pull request, we will only warn on `--select` and
`--extend-select` but not `--fixable`, `--unfixable`, `--ignore`, or
`--extend-fixable`.

Author: zanieb

Cargo.lock

@@ -737,6 +737,42 @@ fn preview_disabled_prefix_empty() {
     "###);
 }
 
+#[test]
+fn preview_disabled_does_not_warn_for_empty_ignore_selections() {
+    // Does not warn that the selection is empty since the user is not trying to enable the rule
+    let args = ["--ignore", "CPY"];
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        .args(args)
+        .pass_stdin("I=42\n"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    -:1:1: E741 Ambiguous variable name: `I`
+    Found 1 error.
+
+    ----- stderr -----
+    "###);
+}
+
+#[test]
+fn preview_disabled_does_not_warn_for_empty_fixable_selections() {
+    // Does not warn that the selection is empty since the user is not trying to enable the rule
+    let args = ["--fixable", "CPY"];
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        .args(args)
+        .pass_stdin("I=42\n"), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    -:1:1: E741 Ambiguous variable name: `I`
+    Found 1 error.
+
+    ----- stderr -----
+    "###);
+}
+
 #[test]
 fn preview_group_selector() {
     // `--select PREVIEW` should error (selector was removed)

crates/ruff_cli/tests/integration_test.rs

@@ -25,6 +25,7 @@ anyhow = { workspace = true }
 colored = { workspace = true }
 dirs = { version = "5.0.0" }
 ignore = { workspace = true }
+is-macro = { workspace = true }
 itertools = { workspace = true }
 log = { workspace = true }
 glob = { workspace = true }

crates/ruff_workspace/Cargo.toml

@@ -57,6 +57,51 @@ pub struct RuleSelection {
     pub extend_fixable: Vec<RuleSelector>,
 }
 
+#[derive(Debug, Eq, PartialEq, is_macro::Is)]
+pub enum RuleSelectorKind {
+    /// Enables the selected rules
+    Enable,
+    /// Disables the selected rules
+    Disable,
+    /// Modifies the behavior of selected rules
+    Modify,
+}
+
+impl RuleSelection {
+    pub fn selectors_by_kind(&self) -> impl Iterator<Item = (RuleSelectorKind, &RuleSelector)> {
+        self.select
+            .iter()
+            .flatten()
+            .map(|selector| (RuleSelectorKind::Enable, selector))
+            .chain(
+                self.fixable
+                    .iter()
+                    .flatten()
+                    .map(|selector| (RuleSelectorKind::Modify, selector)),
+            )
+            .chain(
+                self.ignore
+                    .iter()
+                    .map(|selector| (RuleSelectorKind::Disable, selector)),
+            )
+            .chain(
+                self.extend_select
+                    .iter()
+                    .map(|selector| (RuleSelectorKind::Enable, selector)),
+            )
+            .chain(
+                self.unfixable
+                    .iter()
+                    .map(|selector| (RuleSelectorKind::Modify, selector)),
+            )
+            .chain(
+                self.extend_fixable
+                    .iter()
+                    .map(|selector| (RuleSelectorKind::Modify, selector)),
+            )
+    }
+}
+
 #[derive(Debug, Default)]
 pub struct Configuration {
     // Global options
@@ -704,16 +749,7 @@ impl LintConfiguration {
             }
 
             // Check for selections that require a warning
-            for selector in selection
-                .select
-                .iter()
-                .chain(selection.fixable.iter())
-                .flatten()
-                .chain(selection.ignore.iter())
-                .chain(selection.extend_select.iter())
-                .chain(selection.unfixable.iter())
-                .chain(selection.extend_fixable.iter())
-            {
+            for (kind, selector) in selection.selectors_by_kind() {
                 #[allow(deprecated)]
                 if matches!(selector, RuleSelector::Nursery) {
                     let suggestion = if preview.mode.is_disabled() {
@@ -725,7 +761,9 @@ impl LintConfiguration {
                     warn_user_once!("The `NURSERY` selector has been deprecated.{suggestion}");
                 };
 
-                if preview.mode.is_disabled() {
+                // Only warn for the following selectors if used to enable rules
+                // e.g. use with `--ignore` or `--fixable` is okay
+                if preview.mode.is_disabled() && kind.is_enable() {
                     if let RuleSelector::Rule { prefix, .. } = selector {
                         if prefix.rules().any(|rule| rule.is_nursery()) {
                             deprecated_nursery_selectors.insert(selector);