Add lint long_variable_names

The lint is configurable by using `max-variable-name-length` and it is set to 100 by default.

Author: JurrianFahner

CHANGELOG.md

@@ -5938,6 +5938,7 @@ Released 2018-09-13
 [`literal_string_with_formatting_args`]: https://rust-lang.github.io/rust-clippy/master/index.html#literal_string_with_formatting_args
 [`little_endian_bytes`]: https://rust-lang.github.io/rust-clippy/master/index.html#little_endian_bytes
 [`logic_bug`]: https://rust-lang.github.io/rust-clippy/master/index.html#logic_bug
+[`long_variable_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#long_variable_names
 [`lossy_float_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#lossy_float_literal
 [`macro_metavars_in_unsafe`]: https://rust-lang.github.io/rust-clippy/master/index.html#macro_metavars_in_unsafe
 [`macro_use_imports`]: https://rust-lang.github.io/rust-clippy/master/index.html#macro_use_imports
@@ -6535,6 +6536,7 @@ Released 2018-09-13
 [`max-struct-bools`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-struct-bools
 [`max-suggested-slice-pattern-length`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-suggested-slice-pattern-length
 [`max-trait-bounds`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-trait-bounds
+[`max-variable-name-length`]: https://doc.rust-lang.org/clippy/lint_configuration.html#max-variable-name-length
 [`min-ident-chars-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#min-ident-chars-threshold
 [`missing-docs-allow-unused`]: https://doc.rust-lang.org/clippy/lint_configuration.html#missing-docs-allow-unused
 [`missing-docs-in-crate-items`]: https://doc.rust-lang.org/clippy/lint_configuration.html#missing-docs-in-crate-items

book/src/lint_configuration.md

@@ -734,6 +734,16 @@ The maximum number of bounds a trait can have to be linted
 * [`type_repetition_in_bounds`](https://rust-lang.github.io/rust-clippy/master/index.html#type_repetition_in_bounds)
 
 
+## `max-variable-name-length`
+The maximum length of a variable
+
+**Default Value:** `100`
+
+---
+**Affected lints:**
+* [`long_variable_names`](https://rust-lang.github.io/rust-clippy/master/index.html#long_variable_names)
+
+
 ## `min-ident-chars-threshold`
 Minimum chars an ident can have, anything below or equal to this will be linted.
 

clippy_config/src/conf.rs

@@ -675,6 +675,9 @@ define_Conf! {
     /// The maximum number of bounds a trait can have to be linted
     #[lints(type_repetition_in_bounds)]
     max_trait_bounds: u64 = 3,
+    /// The maximum length of a variable
+    #[lints(long_variable_names)]
+    max_variable_name_length: u32 = 100,
     /// Minimum chars an ident can have, anything below or equal to this will be linted.
     #[lints(min_ident_chars)]
     min_ident_chars_threshold: u64 = 1,

clippy_lints/src/declared_lints.rs

@@ -260,6 +260,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::literal_representation::UNREADABLE_LITERAL_INFO,
     crate::literal_representation::UNUSUAL_BYTE_GROUPINGS_INFO,
     crate::literal_string_with_formatting_args::LITERAL_STRING_WITH_FORMATTING_ARGS_INFO,
+    crate::long_variable_names::LONG_VARIABLE_NAMES_INFO,
     crate::loops::CHAR_INDICES_AS_BYTE_INDICES_INFO,
     crate::loops::EMPTY_LOOP_INFO,
     crate::loops::EXPLICIT_COUNTER_LOOP_INFO,

clippy_lints/src/lib.rs

@@ -199,6 +199,7 @@ mod lifetimes;
 mod lines_filter_map_ok;
 mod literal_representation;
 mod literal_string_with_formatting_args;
+mod long_variable_names;
 mod loops;
 mod macro_metavars_in_unsafe;
 mod macro_use;
@@ -944,5 +945,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(single_option_map::SingleOptionMap));
     store.register_late_pass(move |_| Box::new(redundant_test_prefix::RedundantTestPrefix));
     store.register_late_pass(|_| Box::new(cloned_ref_to_slice_refs::ClonedRefToSliceRefs::new(conf)));
+    store.register_late_pass(move |_| Box::new(long_variable_names::LongVariableNames::new(conf)));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

clippy_lints/src/long_variable_names.rs

@@ -0,0 +1,76 @@
+use crate::rustc_lint::LintContext;
+use crate::rustc_span::Pos;
+use clippy_config::Conf;
+use clippy_utils::diagnostics::span_lint_and_help;
+use rustc_hir::{Pat, PatKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::impl_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for variable that exceeds a configurable number characters.
+    ///
+    /// ### Why is this bad?
+    /// Long variable names can make code harder to read and thus to maintain.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let ferris_fixes_more_bugs_than_your_entire_devops_team_does = "content of a string";
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let ferris_fixes_more_bugs = "content of a string";
+    /// ```
+    #[clippy::version = "1.88.0"]
+    pub LONG_VARIABLE_NAMES,
+    style,
+    "usage of a long variable"
+}
+pub struct LongVariableNames {
+    pub max_variable_name_length: u32,
+}
+
+impl LongVariableNames {
+    pub fn new(conf: &'static Conf) -> Self {
+        Self {
+            max_variable_name_length: conf.max_variable_name_length,
+        }
+    }
+}
+
+impl_lint_pass!(LongVariableNames => [LONG_VARIABLE_NAMES]);
+
+impl<'tcx> LateLintPass<'tcx> for LongVariableNames {
+    fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
+        if let PatKind::Binding(.., ident, _) = pat.kind {
+            let length_bytes = if ident.span.from_expansion() {
+                // since the span can't be calculated, we can't lint this
+                // so we just return
+                return;
+            } else {
+                let higher_bound = cx.sess().source_map().lookup_char_pos(ident.span.hi()).col;
+                let lower_bound = cx.sess().source_map().lookup_char_pos(ident.span.lo()).col;
+                (higher_bound - lower_bound).to_u32() + 1
+            };
+            if length_bytes > self.max_variable_name_length {
+                let variable_name_length = u32::try_from(ident.name.to_ident_string().chars().count())
+                    .expect("the variable name length exceeds u32::MAX");
+                if variable_name_length > self.max_variable_name_length {
+                    let length_diff = variable_name_length - self.max_variable_name_length;
+
+                    span_lint_and_help(
+                        cx,
+                        LONG_VARIABLE_NAMES,
+                        ident.span,
+                        format!(
+                            "variable name is longer than the configured `max-variable-name-length` of ({} characters)",
+                            self.max_variable_name_length
+                        ),
+                        None,
+                        format!("reduce the length of the variable name with at least {length_diff} characters"),
+                    );
+                }
+            }
+        }
+    }
+}

tests/clippy.toml

@@ -1,2 +1,5 @@
 # default config for tests, overrides clippy.toml at the project root
 lint-commented-code = false
+
+# override the default length of variables to test the configuration
+max-variable-name-length = 50

tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr

@@ -57,6 +57,7 @@ error: error reading Clippy's configuration file: unknown field `foobar`, expect
            max-struct-bools
            max-suggested-slice-pattern-length
            max-trait-bounds
+           max-variable-name-length
            min-ident-chars-threshold
            missing-docs-allow-unused
            missing-docs-in-crate-items
@@ -151,6 +152,7 @@ error: error reading Clippy's configuration file: unknown field `barfoo`, expect
            max-struct-bools
            max-suggested-slice-pattern-length
            max-trait-bounds
+           max-variable-name-length
            min-ident-chars-threshold
            missing-docs-allow-unused
            missing-docs-in-crate-items
@@ -245,6 +247,7 @@ error: error reading Clippy's configuration file: unknown field `allow_mixed_uni
            max-struct-bools
            max-suggested-slice-pattern-length
            max-trait-bounds
+           max-variable-name-length
            min-ident-chars-threshold
            missing-docs-allow-unused
            missing-docs-in-crate-items

tests/ui/long_variable_names.rs

@@ -0,0 +1,15 @@
+#![warn(clippy::long_variable_names)]
+
+fn a_function(ferris_singlehandedly_refactored_the_monolith_while_juggling_crates_and_lifetimes: &str) {
+    //~^ long_variable_names
+}
+
+fn another_function(just_a_short_name: &str) {
+    // should not cause a problem
+}
+
+fn main() {
+    // `ferris_singlehandedly_refactored_the_monolith_while_juggling_crates_and_lifetimes` is too long
+    let ferris_singlehandedly_refactored_the_monolith_while_juggling_crates_and_lifetimes = "very long indeed";
+    //~^ long_variable_names
+}

tests/ui/long_variable_names.stderr

@@ -0,0 +1,20 @@
+error: variable name is longer than the configured `max-variable-name-length` of (50 characters)
+  --> tests/ui/long_variable_names.rs:3:15
+   |
+LL | fn a_function(ferris_singlehandedly_refactored_the_monolith_while_juggling_crates_and_lifetimes: &str) {
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: reduce the length of the variable name with at least 31 characters
+   = note: `-D clippy::long-variable-names` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::long_variable_names)]`
+
+error: variable name is longer than the configured `max-variable-name-length` of (50 characters)
+  --> tests/ui/long_variable_names.rs:13:9
+   |
+LL |     let ferris_singlehandedly_refactored_the_monolith_while_juggling_crates_and_lifetimes = "very long indeed";
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: reduce the length of the variable name with at least 31 characters
+
+error: aborting due to 2 previous errors
+