src/tools/tidy/src/pal.rs

//! Tidy check to enforce rules about platform-specific code in std.
//!
//! This is intended to maintain existing standards of code
//! organization in hopes that the standard library will continue to
//! be refactored to isolate platform-specific bits, making porting
//! easier; where "standard library" roughly means "all the
//! dependencies of the std and test crates".
//!
//! This generally means placing restrictions on where `cfg(unix)`,
//! `cfg(windows)`, `cfg(target_os)` and `cfg(target_env)` may appear,
//! the basic objective being to isolate platform-specific code to the
//! platform-specific `std::sys` modules, and to the allocation,
//! unwinding, and libc crates.
//!
//! Following are the basic rules, though there are currently
//! exceptions:
//!
//! - core may not have platform-specific code.
//! - libpanic_abort may have platform-specific code.
//! - libpanic_unwind may have platform-specific code.
//! - libunwind may have platform-specific code.
//! - other crates in the std facade may not.
//! - std may have platform-specific code in the following places:
//!   - `sys/`
//!   - `os/`
//!
//! `std/sys_common` should _not_ contain platform-specific code.
//! Finally, because std contains tests with platform-specific
//! `ignore` attributes, once the parser encounters `mod tests`,
//! platform-specific cfgs are allowed. Not sure yet how to deal with
//! this in the long term.

use crate::walk::{filter_dirs, walk};
use std::path::Path;

// Paths that may contain platform-specific code.
const EXCEPTION_PATHS: &[&str] = &[
    "library/panic_abort",
    "library/panic_unwind",
    "library/unwind",
    "library/rtstartup", // Not sure what to do about this. magic stuff for mingw
    "library/test",      // Probably should defer to unstable `std::sys` APIs.
    // The `VaList` implementation must have platform specific code.
    // The Windows implementation of a `va_list` is always a character
    // pointer regardless of the target architecture. As a result,
    // we must use `#[cfg(windows)]` to conditionally compile the
    // correct `VaList` structure for windows.
    "library/core/src/ffi/mod.rs",
    "library/std/src/sys/", // Platform-specific code for std lives here.
    "library/std/src/os",   // Platform-specific public interfaces
    // Temporary `std` exceptions
    // FIXME: platform-specific code should be moved to `sys`
    "library/std/src/io/copy.rs",
    "library/std/src/io/stdio.rs",
    "library/std/src/lib.rs", // for miniz_oxide leaking docs, which itself workaround
    "library/std/src/path.rs",
    "library/std/src/sys_common", // Should only contain abstractions over platforms
    "library/std/src/net/test.rs", // Utility helpers for tests
];

pub fn check(path: &Path, bad: &mut bool) {
    // Sanity check that the complex parsing here works.
    let mut saw_target_arch = false;
    let mut saw_cfg_bang = false;
    walk(path, |path, _is_dir| filter_dirs(path), &mut |entry, contents| {
        let file = entry.path();
        let filestr = file.to_string_lossy().replace("\\", "/");
        if !filestr.ends_with(".rs") {
            return;
        }

        let is_exception_path = EXCEPTION_PATHS.iter().any(|s| filestr.contains(&**s));
        if is_exception_path {
            return;
        }

        // exclude tests and benchmarks as some platforms do not support all tests
        if filestr.contains("tests") || filestr.contains("benches") {
            return;
        }

        check_cfgs(contents, &file, bad, &mut saw_target_arch, &mut saw_cfg_bang);
    });

    assert!(saw_target_arch);
    assert!(saw_cfg_bang);
}

fn check_cfgs(
    contents: &str,
    file: &Path,
    bad: &mut bool,
    saw_target_arch: &mut bool,
    saw_cfg_bang: &mut bool,
) {
    // Pull out all `cfg(...)` and `cfg!(...)` strings.
    let cfgs = parse_cfgs(contents);

    let mut line_numbers: Option<Vec<usize>> = None;
    let mut err = |idx: usize, cfg: &str| {
        if line_numbers.is_none() {
            line_numbers = Some(contents.match_indices('\n').map(|(i, _)| i).collect());
        }
        let line_numbers = line_numbers.as_ref().expect("");
        let line = match line_numbers.binary_search(&idx) {
            Ok(_) => unreachable!(),
            Err(i) => i + 1,
        };
        tidy_error!(bad, "{}:{}: platform-specific cfg: {}", file.display(), line, cfg);
    };

    for (idx, cfg) in cfgs {
        // Sanity check that the parsing here works.
        if !*saw_target_arch && cfg.contains("target_arch") {
            *saw_target_arch = true
        }
        if !*saw_cfg_bang && cfg.contains("cfg!") {
            *saw_cfg_bang = true
        }

        let contains_platform_specific_cfg = cfg.contains("target_os")
            || cfg.contains("target_env")
            || cfg.contains("target_abi")
            || cfg.contains("target_vendor")
            || cfg.contains("target_family")
            || cfg.contains("unix")
            || cfg.contains("windows");

        if !contains_platform_specific_cfg {
            continue;
        }

        let preceded_by_doc_comment = {
            let pre_contents = &contents[..idx];
            let pre_newline = pre_contents.rfind('\n');
            let pre_doc_comment = pre_contents.rfind("///");
            match (pre_newline, pre_doc_comment) {
                (Some(n), Some(c)) => n < c,
                (None, Some(_)) => true,
                (_, None) => false,
            }
        };

        if preceded_by_doc_comment {
            continue;
        }

        // exclude tests as some platforms do not support all tests
        if cfg.contains("test") {
            continue;
        }

        err(idx, cfg);
    }
}

fn parse_cfgs(contents: &str) -> Vec<(usize, &str)> {
    let candidate_cfgs = contents.match_indices("cfg");
    let candidate_cfg_idxs = candidate_cfgs.map(|(i, _)| i);
    // This is puling out the indexes of all "cfg" strings
    // that appear to be tokens followed by a parenthesis.
    let cfgs = candidate_cfg_idxs.filter(|i| {
        let pre_idx = i.saturating_sub(1);
        let succeeds_non_ident = !contents
            .as_bytes()
            .get(pre_idx)
            .cloned()
            .map(char::from)
            .map(char::is_alphanumeric)
            .unwrap_or(false);
        let contents_after = &contents[*i..];
        let first_paren = contents_after.find('(');
        let paren_idx = first_paren.map(|ip| i + ip);
        let preceeds_whitespace_and_paren = paren_idx
            .map(|ip| {
                let maybe_space = &contents[*i + "cfg".len()..ip];
                maybe_space.chars().all(|c| char::is_whitespace(c) || c == '!')
            })
            .unwrap_or(false);

        succeeds_non_ident && preceeds_whitespace_and_paren
    });

    cfgs.flat_map(|i| {
        let mut depth = 0;
        let contents_from = &contents[i..];
        for (j, byte) in contents_from.bytes().enumerate() {
            match byte {
                b'(' => {
                    depth += 1;
                }
                b')' => {
                    depth -= 1;
                    if depth == 0 {
                        return Some((i, &contents_from[..=j]));
                    }
                }
                _ => {}
            }
        }

        // if the parentheses are unbalanced just ignore this cfg -- it'll be caught when attempting
        // to run the compiler, and there's no real reason to lint it separately here
        None
    })
    .collect()
}