new lint: single_char_lifetime_names

Author: PatchMixolydic

CHANGELOG.md

@@ -3253,6 +3253,7 @@ Released 2018-09-13
 [`should_implement_trait`]: https://rust-lang.github.io/rust-clippy/master/index.html#should_implement_trait
 [`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_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_component_path_imports`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_component_path_imports
 [`single_element_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#single_element_loop

clippy_lints/src/lib.register_lints.rs

@@ -435,6 +435,7 @@ store.register_lints(&[
     shadow::SHADOW_REUSE,
     shadow::SHADOW_SAME,
     shadow::SHADOW_UNRELATED,
+    single_char_lifetime_names::SINGLE_CHAR_LIFETIME_NAMES,
     single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS,
     size_of_in_element_count::SIZE_OF_IN_ELEMENT_COUNT,
     slow_vector_initialization::SLOW_VECTOR_INITIALIZATION,

clippy_lints/src/lib.register_restriction.rs

@@ -54,6 +54,7 @@ store.register_group(true, "clippy::restriction", Some("clippy_restriction"), ve
     LintId::of(shadow::SHADOW_REUSE),
     LintId::of(shadow::SHADOW_SAME),
     LintId::of(shadow::SHADOW_UNRELATED),
+    LintId::of(single_char_lifetime_names::SINGLE_CHAR_LIFETIME_NAMES),
     LintId::of(strings::STRING_ADD),
     LintId::of(strings::STRING_SLICE),
     LintId::of(strings::STRING_TO_STRING),

clippy_lints/src/lib.rs

@@ -351,6 +351,7 @@ mod self_named_constructors;
 mod semicolon_if_nothing_returned;
 mod serde_api;
 mod shadow;
+mod single_char_lifetime_names;
 mod single_component_path_imports;
 mod size_of_in_element_count;
 mod slow_vector_initialization;
@@ -858,6 +859,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| Box::new(needless_late_init::NeedlessLateInit));
     store.register_late_pass(|| Box::new(return_self_not_must_use::ReturnSelfNotMustUse));
     store.register_late_pass(|| Box::new(init_numbered_fields::NumberedFields));
+    store.register_early_pass(|| Box::new(single_char_lifetime_names::SingleCharLifetimeNames));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/single_char_lifetime_names.rs

@@ -0,0 +1,63 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use rustc_ast::ast::{GenericParam, GenericParamKind};
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for lifetimes with names which are one character
+    /// long.
+    ///
+    /// ### Why is this bad?
+    /// A single character is likely not enough to express the
+    /// purpose of a lifetime. Using a longer name can make code
+    /// easier to understand, especially for those who are new to
+    /// Rust.
+    ///
+    /// ### Known problems
+    /// Rust programmers and learning resources tend to use single
+    /// character lifetimes, so this lint is at odds with the
+    /// ecosystem at large. In addition, the lifetime's purpose may
+    /// be obvious or, rarely, expressible in one character.
+    ///
+    /// ### Example
+    /// ```rust
+    /// struct DiagnosticCtx<'a> {
+    ///     source: &'a str,
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// struct DiagnosticCtx<'src> {
+    ///     source: &'src str,
+    /// }
+    /// ```
+    #[clippy::version = "1.59.0"]
+    pub SINGLE_CHAR_LIFETIME_NAMES,
+    restriction,
+    "warns against single-character lifetime names"
+}
+
+declare_lint_pass!(SingleCharLifetimeNames => [SINGLE_CHAR_LIFETIME_NAMES]);
+
+impl EarlyLintPass for SingleCharLifetimeNames {
+    fn check_generic_param(&mut self, ctx: &EarlyContext<'_>, param: &GenericParam) {
+        if in_external_macro(ctx.sess, param.ident.span) {
+            return;
+        }
+
+        if let GenericParamKind::Lifetime = param.kind {
+            if !param.is_placeholder && param.ident.as_str().len() <= 2 {
+                span_lint_and_help(
+                    ctx,
+                    SINGLE_CHAR_LIFETIME_NAMES,
+                    param.ident.span,
+                    "single-character lifetime names are likely uninformative",
+                    None,
+                    "use a more informative name",
+                );
+            }
+        }
+    }
+}

tests/ui/single_char_lifetime_names.rs

@@ -0,0 +1,33 @@
+#![warn(clippy::single_char_lifetime_names)]
+
+struct DiagnosticCtx<'a, 'b>
+where
+    'a: 'b,
+{
+    _source: &'a str,
+    _unit: &'b (),
+}
+
+impl<'a, 'b> DiagnosticCtx<'a, 'b> {
+    fn new(source: &'a str, unit: &'b ()) -> DiagnosticCtx<'a, 'b> {
+        Self {
+            _source: source,
+            _unit: unit,
+        }
+    }
+}
+
+impl<'src, 'unit> DiagnosticCtx<'src, 'unit> {
+    fn new_pass(source: &'src str, unit: &'unit ()) -> DiagnosticCtx<'src, 'unit> {
+        Self {
+            _source: source,
+            _unit: unit,
+        }
+    }
+}
+
+fn main() {
+    let src = "loop {}";
+    let unit = ();
+    DiagnosticCtx::new(src, &unit);
+}

tests/ui/single_char_lifetime_names.stderr

@@ -0,0 +1,35 @@
+error: single-character lifetime names are likely uninformative
+  --> $DIR/single_char_lifetime_names.rs:3:22
+   |
+LL | struct DiagnosticCtx<'a, 'b>
+   |                      ^^
+   |
+   = note: `-D clippy::single-char-lifetime-names` implied by `-D warnings`
+   = help: use a more informative name
+
+error: single-character lifetime names are likely uninformative
+  --> $DIR/single_char_lifetime_names.rs:3:26
+   |
+LL | struct DiagnosticCtx<'a, 'b>
+   |                          ^^
+   |
+   = help: use a more informative name
+
+error: single-character lifetime names are likely uninformative
+  --> $DIR/single_char_lifetime_names.rs:11:6
+   |
+LL | impl<'a, 'b> DiagnosticCtx<'a, 'b> {
+   |      ^^
+   |
+   = help: use a more informative name
+
+error: single-character lifetime names are likely uninformative
+  --> $DIR/single_char_lifetime_names.rs:11:10
+   |
+LL | impl<'a, 'b> DiagnosticCtx<'a, 'b> {
+   |          ^^
+   |
+   = help: use a more informative name
+
+error: aborting due to 4 previous errors
+