Add excessive_file_length lint

CHANGELOG.md

@@ -6266,6 +6266,7 @@ Released 2018-09-13
 [`err_expect`]: https://rust-lang.github.io/rust-clippy/master/index.html#err_expect
 [`error_impl_error`]: https://rust-lang.github.io/rust-clippy/master/index.html#error_impl_error
 [`eval_order_dependence`]: https://rust-lang.github.io/rust-clippy/master/index.html#eval_order_dependence
+[`excessive_file_length`]: https://rust-lang.github.io/rust-clippy/master/index.html#excessive_file_length
 [`excessive_nesting`]: https://rust-lang.github.io/rust-clippy/master/index.html#excessive_nesting
 [`excessive_precision`]: https://rust-lang.github.io/rust-clippy/master/index.html#excessive_precision
 [`exhaustive_enums`]: https://rust-lang.github.io/rust-clippy/master/index.html#exhaustive_enums

clippy_config/src/conf.rs

@@ -657,6 +657,9 @@ define_Conf! {
     /// The maximum amount of nesting a block can reside in
     #[lints(excessive_nesting)]
     excessive_nesting_threshold: u64 = 0,
+    /// The maximum number of lines a file can have
+    #[lints(excessive_file_length)]
+    excessive_file_length_threshold: u64 = 500,
     /// The maximum byte size a `Future` can have, before it triggers the `clippy::large_futures` lint
     #[lints(large_futures)]
     future_size_threshold: u64 = 16 * 1024,

clippy_lints/src/declared_lints.rs

@@ -152,6 +152,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::eta_reduction::REDUNDANT_CLOSURE_FOR_METHOD_CALLS_INFO,
     crate::excessive_bools::FN_PARAMS_EXCESSIVE_BOOLS_INFO,
     crate::excessive_bools::STRUCT_EXCESSIVE_BOOLS_INFO,
+    crate::excessive_file_length::EXCESSIVE_FILE_LENGTH_INFO,
     crate::excessive_nesting::EXCESSIVE_NESTING_INFO,
     crate::exhaustive_items::EXHAUSTIVE_ENUMS_INFO,
     crate::exhaustive_items::EXHAUSTIVE_STRUCTS_INFO,

clippy_lints/src/excessive_file_length.rs

@@ -0,0 +1,99 @@
+use clippy_config::Conf;
+use clippy_utils::diagnostics::span_lint_and_help;
+use rustc_ast::Crate;
+use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
+use rustc_session::impl_lint_pass;
+use rustc_span::def_id::LOCAL_CRATE;
+use rustc_span::{FileName, Span, SyntaxContext};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for files that exceed a configurable line count threshold.
+    ///
+    /// Note: This is a restriction lint that is allow-by-default. You need to enable it
+    /// explicitly in your configuration and set the threshold in clippy.toml.
+    ///
+    /// ### Why restrict this?
+    /// Large files can be harder to navigate and understand. They often indicate that
+    /// the code could benefit from being split into multiple smaller, more focused modules.
+    /// This improves maintainability and makes the codebase easier to understand.
+    ///
+    /// ### Example
+    /// An example clippy.toml configuration:
+    /// ```toml
+    /// # clippy.toml
+    /// excessive-file-length-threshold = 500
+    /// ```
+    ///
+    /// If a file exceeds this threshold, the lint will suggest splitting it into
+    /// smaller modules.
+    #[clippy::version = "1.84.0"]
+    pub EXCESSIVE_FILE_LENGTH,
+    restriction,
+    "checks for files that exceed a configurable line count threshold"
+}
+
+impl_lint_pass!(ExcessiveFileLength => [EXCESSIVE_FILE_LENGTH]);
+
+pub struct ExcessiveFileLength {
+    pub excessive_file_length_threshold: u64,
+}
+
+impl ExcessiveFileLength {
+    pub fn new(conf: &'static Conf) -> Self {
+        Self {
+            excessive_file_length_threshold: conf.excessive_file_length_threshold,
+        }
+    }
+}
+
+impl EarlyLintPass for ExcessiveFileLength {
+    fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &Crate) {
+        // Only check if threshold is set (non-zero)
+        if self.excessive_file_length_threshold == 0 {
+            return;
+        }
+
+        // Get all source files for the local crate
+        let source_map = cx.sess().source_map();
+
+        // We want to check each file in the current crate
+        for file in source_map.files().iter() {
+            // Only check files from the local crate, not external dependencies
+            if file.cnum != LOCAL_CRATE {
+                continue;
+            }
+
+            // Skip non-real files (generated code, etc.)
+            if !matches!(&file.name, FileName::Real(_)) {
+                continue;
+            }
+
+            // Count total lines in the file
+            let line_count = file.count_lines() as u64;
+
+            // Check if file exceeds threshold
+            if line_count > self.excessive_file_length_threshold {
+                // Create a span at the start of the file for the lint
+                let span = Span::new(
+                    file.start_pos,
+                    file.start_pos,
+                    SyntaxContext::root(),
+                    None,
+                );
+
+                span_lint_and_help(
+                    cx,
+                    EXCESSIVE_FILE_LENGTH,
+                    span,
+                    format!(
+                        "this file has too many lines ({}/{})",
+                        line_count, self.excessive_file_length_threshold
+                    ),
+                    None,
+                    "consider splitting this file into smaller modules to improve maintainability",
+                );
+            }
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -128,6 +128,7 @@ mod error_impl_error;
 mod escape;
 mod eta_reduction;
 mod excessive_bools;
+mod excessive_file_length;
 mod excessive_nesting;
 mod exhaustive_items;
 mod exit;
@@ -747,6 +748,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
     store.register_late_pass(|_| Box::new(tests_outside_test_module::TestsOutsideTestModule));
     store.register_late_pass(|_| Box::new(manual_slice_size_calculation::ManualSliceSizeCalculation::new(conf)));
     store.register_early_pass(move || Box::new(excessive_nesting::ExcessiveNesting::new(conf)));
+    store.register_early_pass(move || Box::new(excessive_file_length::ExcessiveFileLength::new(conf)));
     store.register_late_pass(|_| Box::new(items_after_test_module::ItemsAfterTestModule));
     store.register_early_pass(|| Box::new(ref_patterns::RefPatterns));
     store.register_late_pass(|_| Box::new(default_constructed_unit_structs::DefaultConstructedUnitStructs));

tests/ui-toml/excessive_file_length/clippy.toml

@@ -0,0 +1 @@
+excessive-file-length-threshold = 10

tests/ui-toml/excessive_file_length/excessive_file_length.rs

@@ -0,0 +1,16 @@
+#![warn(clippy::excessive_file_length)]
+//~^ ERROR: this file has too many lines
+
+// This file should trigger the lint because it has more than 10 lines
+// (configured in clippy.toml)
+
+fn main() {
+    println!("Line 1");
+    println!("Line 2");
+    println!("Line 3");
+    println!("Line 4");
+    println!("Line 5");
+    println!("Line 6");
+    println!("Line 7");
+    // This file now has more than 10 lines and should trigger the lint
+}

tests/ui-toml/excessive_file_length/excessive_file_length.stderr

@@ -0,0 +1,12 @@
+error: this file has too many lines (16/10)
+  --> tests/ui-toml/excessive_file_length/excessive_file_length.rs:1:1
+   |
+LL | #![warn(clippy::excessive_file_length)]
+   | ^
+   |
+   = help: consider splitting this file into smaller modules to improve maintainability
+   = note: `-D clippy::excessive-file-length` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::excessive_file_length)]`
+
+error: aborting due to 1 previous error
+

tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr

@@ -46,6 +46,7 @@ error: error reading Clippy's configuration file: unknown field `foobar`, expect
            enforced-import-renames
            enum-variant-name-threshold
            enum-variant-size-threshold
+           excessive-file-length-threshold
            excessive-nesting-threshold
            future-size-threshold
            ignore-interior-mutability
@@ -143,6 +144,7 @@ error: error reading Clippy's configuration file: unknown field `barfoo`, expect
            enforced-import-renames
            enum-variant-name-threshold
            enum-variant-size-threshold
+           excessive-file-length-threshold
            excessive-nesting-threshold
            future-size-threshold
            ignore-interior-mutability
@@ -240,6 +242,7 @@ error: error reading Clippy's configuration file: unknown field `allow_mixed_uni
            enforced-import-renames
            enum-variant-name-threshold
            enum-variant-size-threshold
+           excessive-file-length-threshold
            excessive-nesting-threshold
            future-size-threshold
            ignore-interior-mutability