mirror of
https://github.com/rust-lang/rust-clippy
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103 lines
4.1 KiB
Rust
103 lines
4.1 KiB
Rust
//! This LintPass catches both string addition and string addition + assignment
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//!
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//! Note that since we have two lints where one subsumes the other, we try to
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//! disable the subsumed lint unless it has a higher level
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use rustc::lint::*;
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use rustc_front::hir::*;
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use syntax::codemap::Spanned;
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use eq_op::is_exp_equal;
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use utils::{match_type, span_lint, walk_ptrs_ty, get_parent_expr};
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use utils::STRING_PATH;
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/// **What it does:** This lint matches code of the form `x = x + y` (without `let`!). It is `Allow` by default.
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///
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/// **Why is this bad?** Because this expression needs another copy as opposed to `x.push_str(y)` (in practice LLVM will usually elide it, though). Despite [llogiq](https://github.com/llogiq)'s reservations, this lint also is `allow` by default, as some people opine that it's more readable.
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///
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/// **Known problems:** None. Well apart from the lint being `allow` by default. :smile:
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///
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/// **Example:**
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///
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/// ```
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/// let mut x = "Hello".to_owned();
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/// x = x + ", World";
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/// ```
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declare_lint! {
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pub STRING_ADD_ASSIGN,
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Allow,
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"using `x = x + ..` where x is a `String`; suggests using `push_str()` instead"
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}
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/// **What it does:** The `string_add` lint matches all instances of `x + _` where `x` is of type `String`, but only if [`string_add_assign`](#string_add_assign) does *not* match. It is `Allow` by default.
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///
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/// **Why is this bad?** It's not bad in and of itself. However, this particular `Add` implementation is asymmetric (the other operand need not be `String`, but `x` does), while addition as mathematically defined is symmetric, also the `String::push_str(_)` function is a perfectly good replacement. Therefore some dislike it and wish not to have it in their code.
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///
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/// That said, other people think that String addition, having a long tradition in other languages is actually fine, which is why we decided to make this particular lint `allow` by default.
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///
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/// **Known problems:** None
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///
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/// **Example:**
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///
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/// ```
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/// let x = "Hello".to_owned();
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/// x + ", World"
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/// ```
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declare_lint! {
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pub STRING_ADD,
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Allow,
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"using `x + ..` where x is a `String`; suggests using `push_str()` instead"
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}
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#[derive(Copy, Clone)]
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pub struct StringAdd;
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impl LintPass for StringAdd {
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fn get_lints(&self) -> LintArray {
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lint_array!(STRING_ADD, STRING_ADD_ASSIGN)
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}
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}
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impl LateLintPass for StringAdd {
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fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
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if let ExprBinary(Spanned{ node: BiAdd, .. }, ref left, _) = e.node {
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if is_string(cx, left) {
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if let Allow = cx.current_level(STRING_ADD_ASSIGN) {
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// the string_add_assign is allow, so no duplicates
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} else {
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let parent = get_parent_expr(cx, e);
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if let Some(ref p) = parent {
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if let ExprAssign(ref target, _) = p.node {
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// avoid duplicate matches
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if is_exp_equal(cx, target, left) { return; }
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}
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}
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}
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span_lint(cx, STRING_ADD, e.span,
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"you added something to a string. \
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Consider using `String::push_str()` instead");
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}
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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) {
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span_lint(cx, STRING_ADD_ASSIGN, e.span,
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"you assigned the result of adding something to this string. \
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Consider using `String::push_str()` instead");
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}
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}
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}
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}
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fn is_string(cx: &LateContext, e: &Expr) -> bool {
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match_type(cx, walk_ptrs_ty(cx.tcx.expr_ty(e)), &STRING_PATH)
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}
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fn is_add(cx: &LateContext, src: &Expr, target: &Expr) -> bool {
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match src.node {
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ExprBinary(Spanned{ node: BiAdd, .. }, ref left, _) =>
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is_exp_equal(cx, target, left),
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ExprBlock(ref block) => block.stmts.is_empty() &&
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block.expr.as_ref().map_or(false,
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|expr| is_add(cx, expr, target)),
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_ => false
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}
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}
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