ignore generics and allow arbitrary threshold

14 files changed, 270 insertions, 175 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 27a5fc06b07..2d62bfd4f99 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4958,6 +4958,7 @@ Released 2018-09-13
 [`mem_replace_option_with_none`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_option_with_none
 [`mem_replace_with_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_with_default
 [`mem_replace_with_uninit`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_with_uninit
+[`min_ident_chars`]: https://rust-lang.github.io/rust-clippy/master/index.html#min_ident_chars
 [`min_max`]: https://rust-lang.github.io/rust-clippy/master/index.html#min_max
 [`misaligned_transmute`]: https://rust-lang.github.io/rust-clippy/master/index.html#misaligned_transmute
 [`mismatched_target_os`]: https://rust-lang.github.io/rust-clippy/master/index.html#mismatched_target_os
@@ -5155,7 +5156,6 @@ Released 2018-09-13
 [`significant_drop_tightening`]: https://rust-lang.github.io/rust-clippy/master/index.html#significant_drop_tightening
 [`similar_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#similar_names
 [`single_char_add_str`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_char_add_str
-[`single_char_idents`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_char_idents
 [`single_char_lifetime_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_char_lifetime_names
 [`single_char_pattern`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_char_pattern
 [`single_char_push_str`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_char_push_str
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 1c494468226..769774b27c4 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -416,6 +416,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::VERBOSE_FILE_READS_INFO,
     crate::methods::WRONG_SELF_CONVENTION_INFO,
     crate::methods::ZST_OFFSET_INFO,
+    crate::min_ident_chars::MIN_IDENT_CHARS_INFO,
     crate::minmax::MIN_MAX_INFO,
     crate::misc::SHORT_CIRCUIT_STATEMENT_INFO,
     crate::misc::TOPLEVEL_REF_ARG_INFO,
@@ -565,7 +566,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::shadow::SHADOW_SAME_INFO,
     crate::shadow::SHADOW_UNRELATED_INFO,
     crate::significant_drop_tightening::SIGNIFICANT_DROP_TIGHTENING_INFO,
-    crate::single_char_idents::SINGLE_CHAR_IDENTS_INFO,
     crate::single_char_lifetime_names::SINGLE_CHAR_LIFETIME_NAMES_INFO,
     crate::single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS_INFO,
     crate::size_of_in_element_count::SIZE_OF_IN_ELEMENT_COUNT_INFO,
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 463e4a429d1..dcf1c6f64a4 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -197,6 +197,7 @@ mod matches;
 mod mem_forget;
 mod mem_replace;
 mod methods;
+mod min_ident_chars;
 mod minmax;
 mod misc;
 mod misc_early;
@@ -284,7 +285,6 @@ mod semicolon_if_nothing_returned;
 mod serde_api;
 mod shadow;
 mod significant_drop_tightening;
-mod single_char_idents;
 mod single_char_lifetime_names;
 mod single_component_path_imports;
 mod size_of_in_element_count;
@@ -1034,10 +1034,12 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(redundant_type_annotations::RedundantTypeAnnotations));
     store.register_late_pass(|_| Box::new(arc_with_non_send_sync::ArcWithNonSendSync));
     store.register_late_pass(|_| Box::new(needless_if::NeedlessIf));
-    let allowed_idents = conf.allowed_idents.clone();
-    store.register_early_pass(move || {
-        Box::new(single_char_idents::SingleCharIdents {
-            allowed_idents: allowed_idents.clone(),
+    let allowed_idents_below_min_chars = conf.allowed_idents_below_min_chars.clone();
+    let min_ident_chars_threshold = conf.min_ident_chars_threshold;
+    store.register_late_pass(move |_| {
+        Box::new(min_ident_chars::MinIdentChars {
+            allowed_idents_below_min_chars: allowed_idents_below_min_chars.clone(),
+            min_ident_chars_threshold,
         })
     });
     // add lints here, do not remove this comment, it's used in `new_lint`
diff --git a/clippy_lints/src/min_ident_chars.rs b/clippy_lints/src/min_ident_chars.rs
new file mode 100644
index 00000000000..bbe7fc540e9
--- /dev/null
+++ b/clippy_lints/src/min_ident_chars.rs
@@ -0,0 +1,133 @@
+use clippy_utils::{diagnostics::span_lint, is_from_proc_macro};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::{
+    def::{DefKind, Res},
+    intravisit::{walk_item, Visitor},
+    GenericParamKind, HirId, Item, ItemKind, ItemLocalId, Node,
+};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use std::borrow::Cow;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for idents which comprise of a single letter.
+    ///
+    /// Note: This lint can be very noisy when enabled; it may be desirable to only enable it
+    /// temporarily.
+    ///
+    /// ### Why is this bad?
+    /// In many cases it's not, but at times it can severely hinder readability. Some codebases may
+    /// wish to disallow this to improve readability.
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// for m in movies {
+    ///	    let title = m.t;
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust,ignore
+    /// for movie in movies {
+    ///     let title = movie.title;
+    /// }
+    /// ```
+    /// ```
+    #[clippy::version = "1.72.0"]
+    pub MIN_IDENT_CHARS,
+    restriction,
+    "disallows idents that are too short"
+}
+impl_lint_pass!(MinIdentChars => [MIN_IDENT_CHARS]);
+
+#[derive(Clone)]
+pub struct MinIdentChars {
+    pub allowed_idents_below_min_chars: FxHashSet<String>,
+    pub min_ident_chars_threshold: u64,
+}
+
+impl LateLintPass<'_> for MinIdentChars {
+    fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
+        if self.min_ident_chars_threshold == 0 {
+            return;
+        }
+
+        walk_item(&mut IdentVisitor { conf: self, cx }, item);
+    }
+}
+
+struct IdentVisitor<'cx, 'tcx> {
+    conf: &'cx MinIdentChars,
+    cx: &'cx LateContext<'tcx>,
+}
+
+#[expect(clippy::cast_possible_truncation)]
+impl Visitor<'_> for IdentVisitor<'_, '_> {
+    fn visit_id(&mut self, hir_id: HirId) {
+        let Self { conf, cx } = *self;
+        // Reimplementation of `find`, as it uses indexing, which can (and will in async functions) panic.
+        // This should probably be fixed on the rustc side, this is just a temporary workaround.
+        // FIXME: Remove me if/when this is fixed in rustc
+        let node = if hir_id.local_id == ItemLocalId::from_u32(0) {
+            // In this case, we can just use `find`, `Owner`'s `node` field is private anyway so we can't
+            // reimplement it even if we wanted to
+            cx.tcx.hir().find(hir_id)
+        } else {
+            let Some(owner) = cx.tcx.hir_owner_nodes(hir_id.owner).as_owner() else {
+                return;
+            };
+            owner.nodes.get(hir_id.local_id).copied().flatten().map(|p| p.node)
+        };
+        let Some(node) = node else {
+            return;
+        };
+        let Some(ident) = node.ident() else {
+            return;
+        };
+
+        let str = ident.as_str();
+        if !in_external_macro(cx.sess(), ident.span)
+            && str.len() <= conf.min_ident_chars_threshold as usize
+            && !str.is_empty()
+            && conf.allowed_idents_below_min_chars.get(&str.to_owned()).is_none()
+        {
+            if let Node::Item(item) = node && let ItemKind::Use(..) = item.kind {
+                return;
+            }
+            // `struct Awa<T>(T)`
+            //                ^
+            if let Node::PathSegment(path) = node {
+                if let Res::Def(def_kind, ..) = path.res && let DefKind::TyParam = def_kind {
+                    return;
+                }
+                if matches!(path.res, Res::PrimTy(..)) || path.res.opt_def_id().is_some_and(|def_id| !def_id.is_local())
+                {
+                    return;
+                }
+            }
+            // `struct Awa<T>(T)`
+            //             ^
+            if let Node::GenericParam(generic_param) = node
+                && let GenericParamKind::Type { .. } = generic_param.kind
+            {
+                return;
+            }
+
+            if is_from_proc_macro(cx, &ident) {
+                return;
+            }
+
+            let help = if conf.min_ident_chars_threshold == 1 {
+                Cow::Borrowed("this ident consists of a single char")
+            } else {
+                Cow::Owned(format!(
+                    "this ident is too short ({} <= {}) ",
+                    str.len(),
+                    conf.min_ident_chars_threshold
+                ))
+            };
+            span_lint(cx, MIN_IDENT_CHARS, ident.span, &help);
+        }
+    }
+}
diff --git a/clippy_lints/src/single_char_idents.rs b/clippy_lints/src/single_char_idents.rs
deleted file mode 100644
index 17a2ebe93ed..00000000000
--- a/clippy_lints/src/single_char_idents.rs
+++ /dev/null
@@ -1,59 +0,0 @@
-use clippy_utils::{diagnostics::span_lint, source::snippet};
-use itertools::Itertools;
-use rustc_data_structures::fx::FxHashSet;
-use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
-use rustc_middle::lint::in_external_macro;
-use rustc_session::{declare_tool_lint, impl_lint_pass};
-use rustc_span::symbol::Ident;
-
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for idents which comprise of a single letter.
-    ///
-    /// Note: This lint can be very noisy when enabled; it even lints generics! it may be desirable
-    /// to only enable it temporarily.
-    ///
-    /// ### Why is this bad?
-    /// In many cases it's not, but at times it can severely hinder readability. Some codebases may
-    /// wish to disallow this to improve readability.
-    ///
-    /// ### Example
-    /// ```rust,ignore
-    /// for m in movies {
-    ///	    let title = m.t;
-    /// }
-    /// ```
-    /// Use instead:
-    /// ```rust,ignore
-    /// for movie in movies {
-    ///     let title = movie.title;
-    /// }
-    /// ```
-    /// ```
-    #[clippy::version = "1.72.0"]
-    pub SINGLE_CHAR_IDENTS,
-    restriction,
-    "disallows idents that can be represented as a char"
-}
-impl_lint_pass!(SingleCharIdents => [SINGLE_CHAR_IDENTS]);
-
-#[derive(Clone)]
-pub struct SingleCharIdents {
-    pub allowed_idents: FxHashSet<char>,
-}
-
-impl EarlyLintPass for SingleCharIdents {
-    fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
-        let str = ident.name.as_str();
-        let chars = str.chars();
-        if let [char, rest @ ..] = &*chars.collect_vec()
-            && rest.is_empty()
-            && self.allowed_idents.get(char).is_none()
-            && !in_external_macro(cx.sess(), ident.span)
-            // Ignore proc macros. Let's implement `WithSearchPat` for early lints someday :)
-            && snippet(cx, ident.span, str) == str
-        {
-            span_lint(cx, SINGLE_CHAR_IDENTS, ident.span, "this ident comprises of a single char");
-        }
-    }
-}
diff --git a/clippy_lints/src/utils/conf.rs b/clippy_lints/src/utils/conf.rs
index 7b5413647c7..c84d8d8d1f0 100644
--- a/clippy_lints/src/utils/conf.rs
+++ b/clippy_lints/src/utils/conf.rs
@@ -34,7 +34,7 @@ const DEFAULT_DOC_VALID_IDENTS: &[&str] = &[
     "CamelCase",
 ];
 const DEFAULT_DISALLOWED_NAMES: &[&str] = &["foo", "baz", "quux"];
-const DEFAULT_ALLOWED_IDENTS: &[char] = &['i', 'j', 'x', 'y', 'z', 'n'];
+const DEFAULT_ALLOWED_IDENTS_BELOW_MIN_CHARS: &[&str] = &["i", "j", "x", "y", "z", "n"];
 
 /// Holds information used by `MISSING_ENFORCED_IMPORT_RENAMES` lint.
 #[derive(Clone, Debug, Deserialize)]
@@ -523,6 +523,15 @@ define_Conf! {
     ///
     /// Whether to allow module inception if it's not public.
     (allow_private_module_inception: bool = false),
+    /// Lint: MIN_IDENT_CHARS.
+    ///
+    /// Allowed names below the minimum allowed characters.
+    (allowed_idents_below_min_chars: rustc_data_structures::fx::FxHashSet<String> =
+        super::DEFAULT_ALLOWED_IDENTS_BELOW_MIN_CHARS.iter().map(ToString::to_string).collect()),
+    /// Lint: MIN_IDENT_CHARS.
+    ///
+    /// Minimum chars an ident can have, anything below or equal to this will be linted.
+    (min_ident_chars_threshold: u64 = 1),
 }
 
 /// Search for the configuration file.
diff --git a/tests/ui-toml/min_ident_chars/auxiliary/extern_types.rs b/tests/ui-toml/min_ident_chars/auxiliary/extern_types.rs
new file mode 100644
index 00000000000..06a144f2218
--- /dev/null
+++ b/tests/ui-toml/min_ident_chars/auxiliary/extern_types.rs
@@ -0,0 +1,3 @@
+#![allow(nonstandard_style, unused)]
+
+pub struct Aaa;
diff --git a/tests/ui-toml/min_ident_chars/clippy.toml b/tests/ui-toml/min_ident_chars/clippy.toml
new file mode 100644
index 00000000000..0114ca75014
--- /dev/null
+++ b/tests/ui-toml/min_ident_chars/clippy.toml
@@ -0,0 +1,2 @@
+allowed-idents-below-min-chars = ["Owo", "Uwu", "wha", "t_e", "lse", "_do", "_i_", "put", "her", "_e"]
+min-ident-chars-threshold = 3
diff --git a/tests/ui-toml/min_ident_chars/min_ident_chars.rs b/tests/ui-toml/min_ident_chars/min_ident_chars.rs
new file mode 100644
index 00000000000..33100119ca5
--- /dev/null
+++ b/tests/ui-toml/min_ident_chars/min_ident_chars.rs
@@ -0,0 +1,17 @@
+//@aux-build:extern_types.rs
+#![allow(nonstandard_style, unused)]
+#![warn(clippy::min_ident_chars)]
+
+extern crate extern_types;
+use extern_types::Aaa;
+
+struct Owo {
+    Uwu: u128,
+    aaa: Aaa,
+}
+
+fn main() {
+    let wha = 1;
+    let vvv = 1;
+    let uuu = 1;
+}
diff --git a/tests/ui-toml/min_ident_chars/min_ident_chars.stderr b/tests/ui-toml/min_ident_chars/min_ident_chars.stderr
new file mode 100644
index 00000000000..541f5b10051
--- /dev/null
+++ b/tests/ui-toml/min_ident_chars/min_ident_chars.stderr
@@ -0,0 +1,16 @@
+error: this ident is too short (3 <= 3) 
+  --> $DIR/min_ident_chars.rs:6:19
+   |
+LL | use extern_types::Aaa;
+   |                   ^^^
+   |
+   = note: `-D clippy::min-ident-chars` implied by `-D warnings`
+
+error: this ident is too short (3 <= 3) 
+  --> $DIR/min_ident_chars.rs:10:5
+   |
+LL |     aaa: Aaa,
+   |     ^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr b/tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr
index 2bc872e07e8..c546d95eb46 100644
--- a/tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr
+++ b/tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr
@@ -5,7 +5,7 @@ error: error reading Clippy's configuration file: unknown field `foobar`, expect
            allow-print-in-tests
            allow-private-module-inception
            allow-unwrap-in-tests
-           allowed-idents
+           allowed-idents-below-min-chars
            allowed-scripts
            arithmetic-side-effects-allowed
            arithmetic-side-effects-allowed-binary
@@ -37,6 +37,7 @@ error: error reading Clippy's configuration file: unknown field `foobar`, expect
            max-struct-bools
            max-suggested-slice-pattern-length
            max-trait-bounds
+           min-ident-chars-threshold
            missing-docs-in-crate-items
            msrv
            pass-by-value-size-limit
@@ -69,7 +70,7 @@ error: error reading Clippy's configuration file: unknown field `barfoo`, expect
            allow-print-in-tests
            allow-private-module-inception
            allow-unwrap-in-tests
-           allowed-idents
+           allowed-idents-below-min-chars
            allowed-scripts
            arithmetic-side-effects-allowed
            arithmetic-side-effects-allowed-binary
@@ -101,6 +102,7 @@ error: error reading Clippy's configuration file: unknown field `barfoo`, expect
            max-struct-bools
            max-suggested-slice-pattern-length
            max-trait-bounds
+           min-ident-chars-threshold
            missing-docs-in-crate-items
            msrv
            pass-by-value-size-limit
diff --git a/tests/ui/single_char_idents.rs b/tests/ui/min_ident_chars.rs
index 386633161fe..134c17c553f 100644
--- a/tests/ui/single_char_idents.rs
+++ b/tests/ui/min_ident_chars.rs
@@ -1,6 +1,6 @@
 //@aux-build:proc_macros.rs
 #![allow(nonstandard_style, unused)]
-#![warn(clippy::single_char_idents)]
+#![warn(clippy::min_ident_chars)]
 
 extern crate proc_macros;
 use proc_macros::external;
@@ -38,11 +38,11 @@ fn main() {
     let w = 1;
     // Ok, not this one
     // let i = 1;
-    let j = 1;
-    let n = 1;
-    let x = 1;
-    let y = 1;
-    let z = 1;
+    let jz = 1;
+    let nz = 1;
+    let zx = 1;
+    let yz = 1;
+    let zz = 1;
 
     for j in 0..1000 {}
 
diff --git a/tests/ui/min_ident_chars.stderr b/tests/ui/min_ident_chars.stderr
new file mode 100644
index 00000000000..4b887617058
--- /dev/null
+++ b/tests/ui/min_ident_chars.stderr
@@ -0,0 +1,70 @@
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:9:8
+   |
+LL | struct A {
+   |        ^
+   |
+   = note: `-D clippy::min-ident-chars` implied by `-D warnings`
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:10:5
+   |
+LL |     a: u32,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:12:5
+   |
+LL |     A: u32,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:13:5
+   |
+LL |     I: u32,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:16:8
+   |
+LL | struct B(u32);
+   |        ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:20:6
+   |
+LL | enum C {
+   |      ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:21:5
+   |
+LL |     D,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:22:5
+   |
+LL |     E,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:23:5
+   |
+LL |     F,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:31:5
+   |
+LL |     w: u32,
+   |     ^
+
+error: this ident consists of a single char
+  --> $DIR/min_ident_chars.rs:58:4
+   |
+LL | fn b() {}
+   |    ^
+
+error: aborting due to 11 previous errors
+
diff --git a/tests/ui/single_char_idents.stderr b/tests/ui/single_char_idents.stderr
deleted file mode 100644
index ceedab9c0da..00000000000
--- a/tests/ui/single_char_idents.stderr
+++ /dev/null
@@ -1,100 +0,0 @@
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:9:8
-   |
-LL | struct A {
-   |        ^
-   |
-   = note: `-D clippy::single-char-idents` implied by `-D warnings`
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:10:5
-   |
-LL |     a: u32,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:12:5
-   |
-LL |     A: u32,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:13:5
-   |
-LL |     I: u32,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:16:8
-   |
-LL | struct B(u32);
-   |        ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:20:6
-   |
-LL | enum C {
-   |      ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:21:5
-   |
-LL |     D,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:22:5
-   |
-LL |     E,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:23:5
-   |
-LL |     F,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:31:5
-   |
-LL |     w: u32,
-   |     ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:34:11
-   |
-LL | struct AA<T, E>(T, E);
-   |           ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:34:14
-   |
-LL | struct AA<T, E>(T, E);
-   |              ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:34:17
-   |
-LL | struct AA<T, E>(T, E);
-   |                 ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:34:20
-   |
-LL | struct AA<T, E>(T, E);
-   |                    ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:38:9
-   |
-LL |     let w = 1;
-   |         ^
-
-error: this ident comprises of a single char
-  --> $DIR/single_char_idents.rs:58:4
-   |
-LL | fn b() {}
-   |    ^
-
-error: aborting due to 16 previous errors
-