rust-clippy/src/strings.rs

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//! This LintPass catches both string addition and string addition + assignment
//!
//! Note that since we have two lints where one subsumes the other, we try to
//! disable the subsumed lint unless it has a higher level
use rustc::lint::*;
use syntax::ast::*;
use syntax::codemap::Spanned;
use eq_op::is_exp_equal;
use utils::{match_type, span_lint, walk_ptrs_ty, get_parent_expr};
use utils::STRING_PATH;
declare_lint! {
pub STRING_ADD_ASSIGN,
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Allow,
"using `x = x + ..` where x is a `String`; suggests using `push_str()` instead"
}
declare_lint! {
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pub STRING_ADD,
Allow,
"using `x + ..` where x is a `String`; suggests using `push_str()` instead"
}
#[derive(Copy, Clone)]
pub struct StringAdd;
impl LintPass for StringAdd {
fn get_lints(&self) -> LintArray {
lint_array!(STRING_ADD, STRING_ADD_ASSIGN)
}
fn check_expr(&mut self, cx: &Context, e: &Expr) {
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if let &ExprBinary(Spanned{ node: BiAdd, .. }, ref left, _) = &e.node {
if is_string(cx, left) {
if let Allow = cx.current_level(STRING_ADD_ASSIGN) {
// the string_add_assign is allow, so no duplicates
} else {
let parent = get_parent_expr(cx, e);
if let Some(ref p) = parent {
if let &ExprAssign(ref target, _) = &p.node {
// avoid duplicate matches
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if is_exp_equal(cx, target, left) { return; }
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}
}
}
//TODO check for duplicates
span_lint(cx, STRING_ADD, e.span,
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"you added something to a string. \
Consider using `String::push_str()` instead")
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}
} else if let &ExprAssign(ref target, ref src) = &e.node {
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if is_string(cx, target) && is_add(cx, src, target) {
span_lint(cx, STRING_ADD_ASSIGN, e.span,
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"you assigned the result of adding something to this string. \
Consider using `String::push_str()` instead")
}
}
}
}
fn is_string(cx: &Context, e: &Expr) -> bool {
match_type(cx, walk_ptrs_ty(cx.tcx.expr_ty(e)), &STRING_PATH)
}
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fn is_add(cx: &Context, src: &Expr, target: &Expr) -> bool {
match &src.node {
&ExprBinary(Spanned{ node: BiAdd, .. }, ref left, _) =>
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is_exp_equal(cx, target, left),
&ExprBlock(ref block) => block.stmts.is_empty() &&
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block.expr.as_ref().map_or(false,
|expr| is_add(cx, &*expr, target)),
&ExprParen(ref expr) => is_add(cx, &*expr, target),
_ => false
}
}