tidy/

style.rs

//! Tidy check to enforce various stylistic guidelines on the Rust codebase.
//!
//! Example checks are:
//!
//! * No lines over 100 characters (in non-Rust files).
//! * No files with over 3000 lines (in non-Rust files).
//! * No tabs.
//! * No trailing whitespace.
//! * No CR characters.
//! * No `TODO` or `XXX` directives.
//! * No unexplained ` ```ignore ` or ` ```rust,ignore ` doc tests.
//!
//! Note that some of these rules are excluded from Rust files because we enforce rustfmt. It is
//! preferable to be formatted rather than tidy-clean.
//!
//! A number of these checks can be opted-out of with various directives of the form:
//! `// ignore-tidy-CHECK-NAME`.
// ignore-tidy-dbg

use std::ffi::OsStr;
use std::path::Path;
use std::sync::LazyLock;

use regex::RegexSetBuilder;
use rustc_hash::FxHashMap;

use crate::diagnostics::{CheckId, TidyCtx};
use crate::walk::{filter_dirs, walk};

#[cfg(test)]
mod tests;

/// Error code markdown is restricted to 80 columns because they can be
/// displayed on the console with --example.
const ERROR_CODE_COLS: usize = 80;
const COLS: usize = 100;
const GOML_COLS: usize = 120;

const LINES: usize = 3000;

const UNEXPLAINED_IGNORE_DOCTEST_INFO: &str = r#"unexplained "```ignore" doctest; try one:

* make the test actually pass, by adding necessary imports and declarations, or
* use "```text", if the code is not Rust code, or
* use "```compile_fail,Ennnn", if the code is expected to fail at compile time, or
* use "```should_panic", if the code is expected to fail at run time, or
* use "```no_run", if the code should type-check but not necessary linkable/runnable, or
* explain it like "```ignore (cannot-test-this-because-xxxx)", if the annotation cannot be avoided.

"#;

const LLVM_UNREACHABLE_INFO: &str = r"\
C++ code used llvm_unreachable, which triggers undefined behavior
when executed when assertions are disabled.
Use llvm::report_fatal_error for increased robustness.";

const DOUBLE_SPACE_AFTER_DOT: &str = r"\
Use a single space after dots in comments.";

const ANNOTATIONS_TO_IGNORE: &[&str] = &[
    "// @!has",
    "// @has",
    "// @matches",
    "// CHECK",
    "// EMIT_MIR",
    "// compile-flags",
    "//@ compile-flags",
    "// error-pattern",
    "//@ error-pattern",
    "//@ gdb",
    "//@ lldb",
    "//@ cdb",
    "//@ normalize-stderr",
];

const LINELENGTH_CHECK: &str = "linelength";

// If you edit this, also edit where it gets used in `check` (calling `contains_ignore_directives`)
const CONFIGURABLE_CHECKS: [&str; 11] = [
    "cr",
    "undocumented-unsafe",
    "tab",
    LINELENGTH_CHECK,
    "filelength",
    "end-whitespace",
    "trailing-newlines",
    "leading-newlines",
    "copyright",
    "dbg",
    "odd-backticks",
];

fn generate_problems<'a>(
    consts: &'a [u32],
    letter_digit: &'a FxHashMap<char, char>,
) -> impl Iterator<Item = u32> + 'a {
    consts.iter().flat_map(move |const_value| {
        let problem = letter_digit.iter().fold(format!("{const_value:X}"), |acc, (key, value)| {
            acc.replace(&value.to_string(), &key.to_string())
        });
        let indexes: Vec<usize> = problem
            .chars()
            .enumerate()
            .filter_map(|(index, c)| if letter_digit.contains_key(&c) { Some(index) } else { None })
            .collect();
        (0..1 << indexes.len()).map(move |i| {
            u32::from_str_radix(
                &problem
                    .chars()
                    .enumerate()
                    .map(|(index, c)| {
                        if let Some(pos) = indexes.iter().position(|&x| x == index) {
                            if (i >> pos) & 1 == 1 { letter_digit[&c] } else { c }
                        } else {
                            c
                        }
                    })
                    .collect::<String>(),
                0x10,
            )
            .unwrap()
        })
    })
}

// Intentionally written in decimal rather than hex
const ROOT_PROBLEMATIC_CONSTS: &[u32] = &[
    184594741, 2880289470, 2881141438, 2965027518, 2976579765, 3203381950, 3405691582, 3405697037,
    3735927486, 3735932941, 4027431614, 4276992702, 195934910, 252707358, 762133, 179681982,
    173390526, 721077,
];

const LETTER_DIGIT: &[(char, char)] = &[('A', '4'), ('B', '8'), ('E', '3')];

// Returns all permutations of problematic consts, over 2000 elements.
fn generate_problematic_strings(
    consts: &[u32],
    letter_digit: &FxHashMap<char, char>,
) -> Vec<String> {
    generate_problems(consts, letter_digit)
        .flat_map(|v| vec![v.to_string(), format!("{:X}", v)])
        .collect()
}

static PROBLEMATIC_CONSTS_STRINGS: LazyLock<Vec<String>> = LazyLock::new(|| {
    generate_problematic_strings(ROOT_PROBLEMATIC_CONSTS, &LETTER_DIGIT.iter().cloned().collect())
});

fn contains_problematic_const(trimmed: &str) -> bool {
    PROBLEMATIC_CONSTS_STRINGS.iter().any(|s| trimmed.to_uppercase().contains(s))
}

const INTERNAL_COMPILER_DOCS_LINE: &str = "#### This error code is internal to the compiler and will not be emitted with normal Rust code.";

/// Parser states for `line_is_url`.
#[derive(Clone, Copy, PartialEq)]
#[allow(non_camel_case_types)]
enum LIUState {
    EXP_COMMENT_START,
    EXP_LINK_LABEL_OR_URL,
    EXP_URL,
    EXP_END,
}

/// Returns `true` if `line` appears to be a line comment containing a URL,
/// possibly with a Markdown link label in front, and nothing else.
/// The Markdown link label, if present, may not contain whitespace.
/// Lines of this form are allowed to be overlength, because Markdown
/// offers no way to split a line in the middle of a URL, and the lengths
/// of URLs to external references are beyond our control.
fn line_is_url(is_error_code: bool, columns: usize, line: &str) -> bool {
    // more basic check for markdown, to avoid complexity in implementing two state machines
    if is_error_code {
        return line.starts_with('[') && line.contains("]:") && line.contains("http");
    }

    use self::LIUState::*;
    let mut state: LIUState = EXP_COMMENT_START;
    let is_url = |w: &str| w.starts_with("http://") || w.starts_with("https://");

    for tok in line.split_whitespace() {
        match (state, tok) {
            (EXP_COMMENT_START, "//") | (EXP_COMMENT_START, "///") | (EXP_COMMENT_START, "//!") => {
                state = EXP_LINK_LABEL_OR_URL
            }

            (EXP_LINK_LABEL_OR_URL, w)
                if w.len() >= 4 && w.starts_with('[') && w.ends_with("]:") =>
            {
                state = EXP_URL
            }

            (EXP_LINK_LABEL_OR_URL, w) if is_url(w) => state = EXP_END,

            (EXP_URL, w) if is_url(w) || w.starts_with("../") => state = EXP_END,

            (_, w) if w.len() > columns && is_url(w) => state = EXP_END,

            (_, _) => {}
        }
    }

    state == EXP_END
}

/// Returns `true` if `line` can be ignored. This is the case when it contains
/// an annotation that is explicitly ignored.
fn should_ignore(line: &str) -> bool {
    // Matches test annotations like `//~ ERROR text`.
    // This mirrors the regex in src/tools/compiletest/src/runtest.rs, please
    // update both if either are changed.
    static_regex!("\\s*//(\\[.*\\])?~.*").is_match(line)
        || ANNOTATIONS_TO_IGNORE.iter().any(|a| line.contains(a))

    // For `ui_test`-style UI test directives, also ignore
    // - `//@[rev] compile-flags`
    // - `//@[rev] normalize-stderr`
        || static_regex!("\\s*//@(\\[.*\\]) (compile-flags|normalize-stderr|error-pattern).*")
            .is_match(line)
        // Matching for rustdoc tests commands.
        // It allows to prevent them emitting warnings like `line longer than 100 chars`.
        || static_regex!(
            "\\s*//@ \\!?(count|files|has|has-dir|hasraw|matches|matchesraw|snapshot)\\s.*"
        ).is_match(line)
}

/// Returns `true` if `line` is allowed to be longer than the normal limit.
fn long_line_is_ok(extension: &str, is_error_code: bool, max_columns: usize, line: &str) -> bool {
    match extension {
        // fluent files are allowed to be any length
        "ftl" => true,
        // non-error code markdown is allowed to be any length
        "md" if !is_error_code => true,
        // HACK(Ezrashaw): there is no way to split a markdown header over multiple lines
        "md" if line == INTERNAL_COMPILER_DOCS_LINE => true,
        _ => line_is_url(is_error_code, max_columns, line) || should_ignore(line),
    }
}

#[derive(Clone, Copy)]
enum Directive {
    /// By default, tidy always warns against style issues.
    Deny,

    /// `Ignore(false)` means that an `ignore-tidy-*` directive
    /// has been provided, but is unnecessary. `Ignore(true)`
    /// means that it is necessary (i.e. a warning would be
    /// produced if `ignore-tidy-*` was not present).
    Ignore(bool),
}

// Use a fixed size array in the return type to catch mistakes with changing `CONFIGURABLE_CHECKS`
// without changing the code in `check` easier.
fn contains_ignore_directives<const N: usize>(
    path_str: &str,
    can_contain: bool,
    contents: &str,
    checks: [&str; N],
) -> [Directive; N] {
    // The rustdoc-json test syntax often requires very long lines, so the checks
    // for long lines aren't really useful.
    let always_ignore_linelength = path_str.contains("rustdoc-json");

    if !can_contain && !always_ignore_linelength {
        return [Directive::Deny; N];
    }

    checks.map(|check| {
        if check == LINELENGTH_CHECK && always_ignore_linelength {
            return Directive::Ignore(false);
        }

        // Update `can_contain` when changing this
        if contents.contains(&format!("// ignore-tidy-{check}"))
            || contents.contains(&format!("# ignore-tidy-{check}"))
            || contents.contains(&format!("/* ignore-tidy-{check} */"))
            || contents.contains(&format!("<!-- ignore-tidy-{check} -->"))
        {
            Directive::Ignore(false)
        } else {
            Directive::Deny
        }
    })
}

macro_rules! suppressible_tidy_err {
    ($err:ident, $skip:ident, $msg:literal) => {
        if let Directive::Deny = $skip {
            $err(&format!($msg));
        } else {
            $skip = Directive::Ignore(true);
        }
    };
}

pub fn is_in(full_path: &Path, parent_folder_to_find: &str, folder_to_find: &str) -> bool {
    if let Some(parent) = full_path.parent() {
        if parent.file_name().map_or_else(
            || false,
            |f| {
                f == folder_to_find
                    && parent
                        .parent()
                        .and_then(|f| f.file_name())
                        .map_or_else(|| false, |f| f == parent_folder_to_find)
            },
        ) {
            true
        } else {
            is_in(parent, parent_folder_to_find, folder_to_find)
        }
    } else {
        false
    }
}

fn skip_markdown_path(path: &Path) -> bool {
    // These aren't ready for tidy.
    const SKIP_MD: &[&str] = &[
        "src/doc/edition-guide",
        "src/doc/embedded-book",
        "src/doc/nomicon",
        "src/doc/reference",
        "src/doc/rust-by-example",
        "src/doc/rustc-dev-guide",
    ];
    SKIP_MD.iter().any(|p| path.ends_with(p))
}

fn is_unexplained_ignore(extension: &str, line: &str) -> bool {
    if !line.ends_with("```ignore") && !line.ends_with("```rust,ignore") {
        return false;
    }
    if extension == "md" && line.trim().starts_with("//") {
        // Markdown examples may include doc comments with ignore inside a
        // code block.
        return false;
    }
    true
}

pub fn check(path: &Path, tidy_ctx: TidyCtx) {
    let mut check = tidy_ctx.start_check(CheckId::new("style").path(path));

    fn skip(path: &Path, is_dir: bool) -> bool {
        if path.file_name().is_some_and(|name| name.to_string_lossy().starts_with(".#")) {
            // vim or emacs temporary file
            return true;
        }

        if filter_dirs(path) || skip_markdown_path(path) {
            return true;
        }

        // Don't check extensions for directories
        if is_dir {
            return false;
        }

        let extensions = ["rs", "py", "js", "sh", "c", "cpp", "h", "md", "css", "ftl", "goml"];

        // NB: don't skip paths without extensions (or else we'll skip all directories and will only check top level files)
        if path.extension().is_none_or(|ext| !extensions.iter().any(|e| ext == OsStr::new(e))) {
            return true;
        }

        // We only check CSS files in rustdoc.
        path.extension().is_some_and(|e| e == "css") && !is_in(path, "src", "librustdoc")
    }

    // This creates a RegexSet as regex contains performance optimizations to be able to deal with these over
    // 2000 needles efficiently. This runs over the entire source code, so performance matters.
    let problematic_regex = RegexSetBuilder::new(PROBLEMATIC_CONSTS_STRINGS.as_slice())
        .case_insensitive(true)
        .build()
        .unwrap();

    // In some cases, a style check would be triggered by its own implementation
    // or comments. A simple workaround is to just allowlist this file.
    let this_file = Path::new(file!());

    walk(path, skip, &mut |entry, contents| {
        let file = entry.path();
        let path_str = file.to_string_lossy();
        let filename = file.file_name().unwrap().to_string_lossy();

        let is_css_file = filename.ends_with(".css");
        let under_rustfmt = filename.ends_with(".rs") &&
            // This list should ideally be sourced from rustfmt.toml but we don't want to add a toml
            // parser to tidy.
            !file.ancestors().any(|a| {
                (a.ends_with("tests") && a.join("COMPILER_TESTS.md").exists()) ||
                    a.ends_with("src/doc/book")
            });

        if contents.is_empty() {
            check.error(format!("{}: empty file", file.display()));
        }

        let extension = file.extension().unwrap().to_string_lossy();
        let is_error_code = extension == "md" && is_in(file, "src", "error_codes");
        let is_goml_code = extension == "goml";

        let max_columns = if is_error_code {
            ERROR_CODE_COLS
        } else if is_goml_code {
            GOML_COLS
        } else {
            COLS
        };

        // When you change this, also change the `directive_line_starts` variable below
        let can_contain = contents.contains("// ignore-tidy-")
            || contents.contains("# ignore-tidy-")
            || contents.contains("/* ignore-tidy-")
            || contents.contains("<!-- ignore-tidy-");
        // Enable testing ICE's that require specific (untidy)
        // file formats easily eg. `issue-1234-ignore-tidy.rs`
        if filename.contains("ignore-tidy") {
            return;
        }
        // Shell completions are automatically generated
        if let Some(p) = file.parent()
            && p.ends_with(Path::new("src/etc/completions"))
        {
            return;
        }
        let [
            mut skip_cr,
            mut skip_undocumented_unsafe,
            mut skip_tab,
            mut skip_line_length,
            mut skip_file_length,
            mut skip_end_whitespace,
            mut skip_trailing_newlines,
            mut skip_leading_newlines,
            mut skip_copyright,
            mut skip_dbg,
            mut skip_odd_backticks,
        ] = contains_ignore_directives(&path_str, can_contain, contents, CONFIGURABLE_CHECKS);
        let mut leading_new_lines = false;
        let mut trailing_new_lines = 0;
        let mut lines = 0;
        let mut last_safety_comment = false;
        let mut comment_block: Option<(usize, usize)> = None;
        let is_test = file.components().any(|c| c.as_os_str() == "tests")
            || file.file_stem().unwrap() == "tests";
        let is_codegen_test = is_test && file.components().any(|c| c.as_os_str() == "codegen-llvm");
        let is_this_file = file.ends_with(this_file) || this_file.ends_with(file);
        let is_test_for_this_file =
            is_test && file.parent().unwrap().ends_with(this_file.with_extension(""));
        // scanning the whole file for multiple needles at once is more efficient than
        // executing lines times needles separate searches.
        let any_problematic_line =
            !is_this_file && !is_test_for_this_file && problematic_regex.is_match(contents);
        for (i, line) in contents.split('\n').enumerate() {
            if line.is_empty() {
                if i == 0 {
                    leading_new_lines = true;
                }
                trailing_new_lines += 1;
                continue;
            } else {
                trailing_new_lines = 0;
            }

            let trimmed = line.trim();

            if !trimmed.starts_with("//") {
                lines += 1;
            }

            let mut err = |msg: &str| {
                check.error(format!("{}:{}: {msg}", file.display(), i + 1));
            };

            if trimmed.contains("dbg!")
                && !trimmed.starts_with("//")
                && !file.ancestors().any(|a| {
                    (a.ends_with("tests") && a.join("COMPILER_TESTS.md").exists())
                        || a.ends_with("library/alloctests")
                })
                && filename != "tests.rs"
            {
                suppressible_tidy_err!(
                    err,
                    skip_dbg,
                    "`dbg!` macro is intended as a debugging tool. It should not be in version control."
                )
            }

            if is_codegen_test && trimmed.contains("CHECK") && trimmed.ends_with(": br") {
                err("`CHECK: br` and `CHECK-NOT: br` in codegen tests are fragile to false \
                    positives in mangled symbols. Try using `br {{.*}}` instead.")
            }

            if !under_rustfmt
                && line.chars().count() > max_columns
                && !long_line_is_ok(&extension, is_error_code, max_columns, line)
            {
                suppressible_tidy_err!(
                    err,
                    skip_line_length,
                    "line longer than {max_columns} chars"
                );
            }
            if !is_css_file && line.contains('\t') {
                suppressible_tidy_err!(err, skip_tab, "tab character");
            }
            if line.ends_with(' ') || line.ends_with('\t') {
                suppressible_tidy_err!(err, skip_end_whitespace, "trailing whitespace");
            }
            if is_css_file && line.starts_with(' ') {
                err("CSS files use tabs for indent");
            }
            if line.contains('\r') {
                suppressible_tidy_err!(err, skip_cr, "CR character");
            }
            if !is_this_file {
                let directive_line_starts = ["// ", "# ", "/* ", "<!-- "];
                let possible_line_start =
                    directive_line_starts.into_iter().any(|s| line.starts_with(s));
                let contains_potential_directive =
                    possible_line_start && (line.contains("-tidy") || line.contains("tidy-"));
                let has_recognized_ignore_directive =
                    contains_ignore_directives(&path_str, can_contain, line, CONFIGURABLE_CHECKS)
                        .into_iter()
                        .any(|directive| matches!(directive, Directive::Ignore(_)));
                let has_alphabetical_directive = line.contains("tidy-alphabetical-start")
                    || line.contains("tidy-alphabetical-end");
                let has_other_tidy_ignore_directive =
                    line.contains("ignore-tidy-target-specific-tests");
                let has_recognized_directive = has_recognized_ignore_directive
                    || has_alphabetical_directive
                    || has_other_tidy_ignore_directive;
                if contains_potential_directive && (!has_recognized_directive) {
                    err("Unrecognized tidy directive")
                }
                // Allow using TODO in diagnostic suggestions by marking the
                // relevant line with `// ignore-tidy-todo`.
                if trimmed.contains("TODO") && !trimmed.contains("ignore-tidy-todo") {
                    err(
                        "TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME",
                    )
                }
                if trimmed.contains("//") && trimmed.contains(" XXX") {
                    err("Instead of XXX use FIXME")
                }
                if any_problematic_line && contains_problematic_const(trimmed) {
                    err("Don't use magic numbers that spell things (consider 0x12345678)");
                }
            }
            // for now we just check libcore
            if trimmed.contains("unsafe {")
                && !trimmed.starts_with("//")
                && !last_safety_comment
                && file.components().any(|c| c.as_os_str() == "core")
                && !is_test
            {
                suppressible_tidy_err!(err, skip_undocumented_unsafe, "undocumented unsafe");
            }
            if trimmed.contains("// SAFETY:") {
                last_safety_comment = true;
            } else if trimmed.starts_with("//") || trimmed.is_empty() {
                // keep previous value
            } else {
                last_safety_comment = false;
            }
            if (line.starts_with("// Copyright")
                || line.starts_with("# Copyright")
                || line.starts_with("Copyright"))
                && (trimmed.contains("Rust Developers")
                    || trimmed.contains("Rust Project Developers"))
            {
                suppressible_tidy_err!(
                    err,
                    skip_copyright,
                    "copyright notices attributed to the Rust Project Developers are deprecated"
                );
            }
            if !file.components().any(|c| c.as_os_str() == "rustc_baked_icu_data")
                && is_unexplained_ignore(&extension, line)
            {
                err(UNEXPLAINED_IGNORE_DOCTEST_INFO);
            }

            if filename.ends_with(".cpp") && line.contains("llvm_unreachable") {
                err(LLVM_UNREACHABLE_INFO);
            }

            // For now only enforce in compiler
            let is_compiler = || file.components().any(|c| c.as_os_str() == "compiler");

            if is_compiler() {
                if line.contains("//")
                    && line
                        .chars()
                        .collect::<Vec<_>>()
                        .windows(4)
                        .any(|cs| matches!(cs, ['.', ' ', ' ', last] if last.is_alphabetic()))
                {
                    err(DOUBLE_SPACE_AFTER_DOT)
                }

                if filename.ends_with(".ftl") {
                    let line_backticks = trimmed.chars().filter(|ch| *ch == '`').count();
                    if line_backticks % 2 == 1 {
                        suppressible_tidy_err!(err, skip_odd_backticks, "odd number of backticks");
                    }
                } else if trimmed.contains("//") {
                    let (start_line, mut backtick_count) = comment_block.unwrap_or((i + 1, 0));
                    let line_backticks = trimmed.chars().filter(|ch| *ch == '`').count();
                    let comment_text = trimmed.split("//").nth(1).unwrap();
                    // This check ensures that we don't lint for code that has `//` in a string literal
                    if line_backticks % 2 == 1 {
                        backtick_count += comment_text.chars().filter(|ch| *ch == '`').count();
                    }
                    comment_block = Some((start_line, backtick_count));
                } else if let Some((start_line, backtick_count)) = comment_block.take()
                    && backtick_count % 2 == 1
                {
                    let mut err = |msg: &str| {
                        check.error(format!("{}:{start_line}: {msg}", file.display()));
                    };
                    let block_len = (i + 1) - start_line;
                    if block_len == 1 {
                        suppressible_tidy_err!(
                            err,
                            skip_odd_backticks,
                            "comment with odd number of backticks"
                        );
                    } else {
                        suppressible_tidy_err!(
                            err,
                            skip_odd_backticks,
                            "{block_len}-line comment block with odd number of backticks"
                        );
                    }
                }
            }
        }
        if leading_new_lines {
            let mut err = |_| {
                check.error(format!("{}: leading newline", file.display()));
            };
            suppressible_tidy_err!(err, skip_leading_newlines, "missing leading newline");
        }
        let mut err = |msg: &str| {
            check.error(format!("{}: {}", file.display(), msg));
        };
        match trailing_new_lines {
            0 => suppressible_tidy_err!(err, skip_trailing_newlines, "missing trailing newline"),
            1 => {}
            n => suppressible_tidy_err!(
                err,
                skip_trailing_newlines,
                "too many trailing newlines ({n})"
            ),
        };
        if lines > LINES {
            let mut err = |_| {
                check.error(format!(
                    "{}: too many lines ({lines}) (add `// \
                     ignore-tidy-filelength` to the file to suppress this error)",
                    file.display(),
                ));
            };
            suppressible_tidy_err!(err, skip_file_length, "");
        }

        if let Directive::Ignore(false) = skip_cr {
            check.error(format!("{}: ignoring CR characters unnecessarily", file.display()));
        }
        if let Directive::Ignore(false) = skip_tab {
            check.error(format!("{}: ignoring tab characters unnecessarily", file.display()));
        }
        if let Directive::Ignore(false) = skip_end_whitespace {
            check.error(format!("{}: ignoring trailing whitespace unnecessarily", file.display()));
        }
        if let Directive::Ignore(false) = skip_trailing_newlines {
            check.error(format!("{}: ignoring trailing newlines unnecessarily", file.display()));
        }
        if let Directive::Ignore(false) = skip_leading_newlines {
            check.error(format!("{}: ignoring leading newlines unnecessarily", file.display()));
        }
        if let Directive::Ignore(false) = skip_copyright {
            check.error(format!("{}: ignoring copyright unnecessarily", file.display()));
        }
        // We deliberately do not warn about these being unnecessary,
        // that would just lead to annoying churn.
        let _unused = skip_line_length;
        let _unused = skip_file_length;
    });
}