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use crate::{
lints::{
HiddenUnicodeCodepointsDiag, HiddenUnicodeCodepointsDiagLabels,
HiddenUnicodeCodepointsDiagSub,
},
EarlyContext, EarlyLintPass, LintContext,
};
use ast::util::unicode::{contains_text_flow_control_chars, TEXT_FLOW_CONTROL_CHARS};
use rustc_ast as ast;
use rustc_span::{BytePos, Span, Symbol};
declare_lint! {
/// The `text_direction_codepoint_in_literal` lint detects Unicode codepoints that change the
/// visual representation of text on screen in a way that does not correspond to their on
/// memory representation.
///
/// ### Explanation
///
/// The unicode characters `\u{202A}`, `\u{202B}`, `\u{202D}`, `\u{202E}`, `\u{2066}`,
/// `\u{2067}`, `\u{2068}`, `\u{202C}` and `\u{2069}` make the flow of text on screen change
/// its direction on software that supports these codepoints. This makes the text "abc" display
/// as "cba" on screen. By leveraging software that supports these, people can write specially
/// crafted literals that make the surrounding code seem like it's performing one action, when
/// in reality it is performing another. Because of this, we proactively lint against their
/// presence to avoid surprises.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(text_direction_codepoint_in_literal)]
/// fn main() {
/// println!("{:?}", '');
/// }
/// ```
///
/// {{produces}}
///
pub TEXT_DIRECTION_CODEPOINT_IN_LITERAL,
Deny,
"detect special Unicode codepoints that affect the visual representation of text on screen, \
changing the direction in which text flows",
}
declare_lint_pass!(HiddenUnicodeCodepoints => [TEXT_DIRECTION_CODEPOINT_IN_LITERAL]);
impl HiddenUnicodeCodepoints {
fn lint_text_direction_codepoint(
&self,
cx: &EarlyContext<'_>,
text: Symbol,
span: Span,
padding: u32,
point_at_inner_spans: bool,
label: &str,
) {
// Obtain the `Span`s for each of the forbidden chars.
let spans: Vec<_> = text
.as_str()
.char_indices()
.filter_map(|(i, c)| {
TEXT_FLOW_CONTROL_CHARS.contains(&c).then(|| {
let lo = span.lo() + BytePos(i as u32 + padding);
(c, span.with_lo(lo).with_hi(lo + BytePos(c.len_utf8() as u32)))
})
})
.collect();
let count = spans.len();
let labels = point_at_inner_spans
.then_some(HiddenUnicodeCodepointsDiagLabels { spans: spans.clone() });
let sub = if point_at_inner_spans && !spans.is_empty() {
HiddenUnicodeCodepointsDiagSub::Escape { spans }
} else {
HiddenUnicodeCodepointsDiagSub::NoEscape { spans }
};
cx.emit_spanned_lint(
TEXT_DIRECTION_CODEPOINT_IN_LITERAL,
span,
HiddenUnicodeCodepointsDiag { label, count, span_label: span, labels, sub },
);
}
}
impl EarlyLintPass for HiddenUnicodeCodepoints {
fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
if let ast::AttrKind::DocComment(_, comment) = attr.kind {
if contains_text_flow_control_chars(comment.as_str()) {
self.lint_text_direction_codepoint(cx, comment, attr.span, 0, false, "doc comment");
}
}
}
#[inline]
fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
// byte strings are already handled well enough by `EscapeError::NonAsciiCharInByteString`
match &expr.kind {
ast::ExprKind::Lit(token_lit) => {
let text = token_lit.symbol;
if !contains_text_flow_control_chars(text.as_str()) {
return;
}
let padding = match token_lit.kind {
// account for `"` or `'`
ast::token::LitKind::Str | ast::token::LitKind::Char => 1,
// account for `r###"`
ast::token::LitKind::StrRaw(n) => n as u32 + 2,
_ => return,
};
self.lint_text_direction_codepoint(cx, text, expr.span, padding, true, "literal");
}
_ => {}
};
}
}
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