manual_is_ascii_check.rs

use rustc_ast::LitKind::{Byte, Char};
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, PatKind, RangeEnd};
use rustc_lint::{LateContext, LateLintPass};
use rustc_semver::RustcVersion;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{def_id::DefId, sym};

use clippy_utils::{
    diagnostics::span_lint_and_sugg, in_constant, macros::root_macro_call, meets_msrv, msrvs, source::snippet,
};

declare_clippy_lint! {
    /// ### What it does
    /// Suggests to use dedicated built-in methods,
    /// `is_ascii_(lowercase|uppercase|digit)` for checking on corresponding ascii range
    ///
    /// ### Why is this bad?
    /// Using the built-in functions is more readable and makes it
    /// clear that it's not a specific subset of characters, but all
    /// ASCII (lowercase|uppercase|digit) characters.
    /// ### Example
    /// ```rust
    /// fn main() {
    ///     assert!(matches!('x', 'a'..='z'));
    ///     assert!(matches!(b'X', b'A'..=b'Z'));
    ///     assert!(matches!('2', '0'..='9'));
    ///     assert!(matches!('x', 'A'..='Z' | 'a'..='z'));
    /// }
    /// ```
    /// Use instead:
    /// ```rust
    /// fn main() {
    ///     assert!('x'.is_ascii_lowercase());
    ///     assert!(b'X'.is_ascii_uppercase());
    ///     assert!('2'.is_ascii_digit());
    ///     assert!('x'.is_ascii_alphabetic());
    /// }
    /// ```
    #[clippy::version = "1.66.0"]
    pub MANUAL_IS_ASCII_CHECK,
    style,
    "use dedicated method to check ascii range"
}
impl_lint_pass!(ManualIsAsciiCheck => [MANUAL_IS_ASCII_CHECK]);

pub struct ManualIsAsciiCheck {
    msrv: Option<RustcVersion>,
}

impl ManualIsAsciiCheck {
    #[must_use]
    pub fn new(msrv: Option<RustcVersion>) -> Self {
        Self { msrv }
    }
}

#[derive(Debug, PartialEq)]
enum CharRange {
    /// 'a'..='z' | b'a'..=b'z'
    LowerChar,
    /// 'A'..='Z' | b'A'..=b'Z'
    UpperChar,
    /// AsciiLower | AsciiUpper
    FullChar,
    /// '0..=9'
    Digit,
    Otherwise,
}

impl<'tcx> LateLintPass<'tcx> for ManualIsAsciiCheck {
    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
        if !meets_msrv(self.msrv, msrvs::IS_ASCII_DIGIT) {
            return;
        }

        if in_constant(cx, expr.hir_id) && !meets_msrv(self.msrv, msrvs::IS_ASCII_DIGIT_CONST) {
            return;
        }

        let Some(macro_call) = root_macro_call(expr.span) else { return };

        if is_matches_macro(cx, macro_call.def_id) {
            if let ExprKind::Match(recv, [arm, ..], _) = expr.kind {
                let range = check_pat(&arm.pat.kind);

                if let Some(sugg) = match range {
                    CharRange::UpperChar => Some("is_ascii_uppercase"),
                    CharRange::LowerChar => Some("is_ascii_lowercase"),
                    CharRange::FullChar => Some("is_ascii_alphabetic"),
                    CharRange::Digit => Some("is_ascii_digit"),
                    CharRange::Otherwise => None,
                } {
                    let default_snip = "..";
                    // `snippet_with_applicability` may set applicability to `MaybeIncorrect` for
                    // macro span, so we check applicability manually by comparing `recv` is not default.
                    let recv = snippet(cx, recv.span, default_snip);

                    let applicability = if recv == default_snip {
                        Applicability::HasPlaceholders
                    } else {
                        Applicability::MachineApplicable
                    };

                    span_lint_and_sugg(
                        cx,
                        MANUAL_IS_ASCII_CHECK,
                        macro_call.span,
                        "manual check for common ascii range",
                        "try",
                        format!("{recv}.{sugg}()"),
                        applicability,
                    );
                }
            }
        }
    }

    extract_msrv_attr!(LateContext);
}

fn check_pat(pat_kind: &PatKind<'_>) -> CharRange {
    match pat_kind {
        PatKind::Or(pats) => {
            let ranges = pats.iter().map(|p| check_pat(&p.kind)).collect::<Vec<_>>();

            if ranges.len() == 2 && ranges.contains(&CharRange::UpperChar) && ranges.contains(&CharRange::LowerChar) {
                CharRange::FullChar
            } else {
                CharRange::Otherwise
            }
        },
        PatKind::Range(Some(start), Some(end), kind) if *kind == RangeEnd::Included => check_range(start, end),
        _ => CharRange::Otherwise,
    }
}

fn check_range(start: &Expr<'_>, end: &Expr<'_>) -> CharRange {
    if let ExprKind::Lit(start_lit) = &start.kind
        && let ExprKind::Lit(end_lit) = &end.kind {
        match (&start_lit.node, &end_lit.node) {
            (Char('a'), Char('z')) | (Byte(b'a'), Byte(b'z')) => CharRange::LowerChar,
            (Char('A'), Char('Z')) | (Byte(b'A'), Byte(b'Z')) => CharRange::UpperChar,
            (Char('0'), Char('9')) | (Byte(b'0'), Byte(b'9')) => CharRange::Digit,
            _ => CharRange::Otherwise,
        }
    } else {
        CharRange::Otherwise
    }
}

fn is_matches_macro(cx: &LateContext<'_>, macro_def_id: DefId) -> bool {
    if let Some(name) = cx.tcx.get_diagnostic_name(macro_def_id) {
        return sym::matches_macro == name;
    }

    false
}