rust/clippy_lints/src/unicode.rs

use rustc::lint::*;
use rustc::hir::*;
use syntax::ast::LitKind;
use syntax::codemap::Span;
use unicode_normalization::UnicodeNormalization;
use utils::{snippet, span_help_and_lint};

/// **What it does:** This lint checks for the Unicode zero-width space in the code.
///
/// **Why is this bad?** Having an invisible character in the code makes for all sorts of April
/// fools, but otherwise is very much frowned upon.
///
/// **Known problems:** None
///
/// **Example:** You don't see it, but there may be a zero-width space somewhere in this text.
declare_lint! {
    pub ZERO_WIDTH_SPACE, Deny,
    "using a zero-width space in a string literal, which is confusing"
}

/// **What it does:** This lint checks for non-ASCII characters in string literals.
///
/// **Why is this bad?** Yeah, we know, the 90's called and wanted their charset back. Even so,
/// there still are editors and other programs out there that don't work well with Unicode. So if
/// the code is meant to be used internationally, on multiple operating systems, or has other
/// portability requirements, activating this lint could be useful.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// let x = "Hä?"
/// ```
declare_lint! {
    pub NON_ASCII_LITERAL, Allow,
    "using any literal non-ASCII chars in a string literal; suggests \
     using the `\\u` escape instead"
}

/// **What it does:** This lint checks for string literals that contain Unicode in a form that is
/// not equal to its [NFC-recomposition](http://www.unicode.org/reports/tr15/#Norm_Forms).
///
/// **Why is this bad?** If such a string is compared to another, the results may be surprising.
///
/// **Known problems** None
///
/// **Example:** You may not see it, but “à” and “à” aren't the same string. The former when
/// escaped is actually `"a\u{300}"` while the latter is `"\u{e0}"`.
declare_lint! {
    pub UNICODE_NOT_NFC, Allow,
    "using a unicode literal not in NFC normal form (see \
     [unicode tr15](http://www.unicode.org/reports/tr15/) for further information)"
}


#[derive(Copy, Clone)]
pub struct Unicode;

impl LintPass for Unicode {
    fn get_lints(&self) -> LintArray {
        lint_array!(ZERO_WIDTH_SPACE, NON_ASCII_LITERAL, UNICODE_NOT_NFC)
    }
}

impl LateLintPass for Unicode {
    fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
        if let ExprLit(ref lit) = expr.node {
            if let LitKind::Str(_, _) = lit.node {
                check_str(cx, lit.span)
            }
        }
    }
}

fn escape<T: Iterator<Item = char>>(s: T) -> String {
    let mut result = String::new();
    for c in s {
        if c as u32 > 0x7F {
            for d in c.escape_unicode() {
                result.push(d)
            }
        } else {
            result.push(c);
        }
    }
    result
}

fn check_str(cx: &LateContext, span: Span) {
    let string = snippet(cx, span, "");
    if string.contains('\u{200B}') {
        span_help_and_lint(cx,
                           ZERO_WIDTH_SPACE,
                           span,
                           "zero-width space detected",
                           &format!("Consider replacing the string with:\n\"{}\"",
                                    string.replace("\u{200B}", "\\u{200B}")));
    }
    if string.chars().any(|c| c as u32 > 0x7F) {
        span_help_and_lint(cx,
                           NON_ASCII_LITERAL,
                           span,
                           "literal non-ASCII character detected",
                           &format!("Consider replacing the string with:\n\"{}\"",
                                    if cx.current_level(UNICODE_NOT_NFC) == Level::Allow {
                                        escape(string.chars())
                                    } else {
                                        escape(string.nfc())
                                    }));
    }
    if cx.current_level(NON_ASCII_LITERAL) == Level::Allow && string.chars().zip(string.nfc()).any(|(a, b)| a != b) {
        span_help_and_lint(cx,
                           UNICODE_NOT_NFC,
                           span,
                           "non-nfc unicode sequence detected",
                           &format!("Consider replacing the string with:\n\"{}\"", string.nfc().collect::<String>()));
    }
}