rust/clippy_lints/src/identity_conversion.rs

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use rustc::lint::*;
use rustc::hir::*;
use syntax::ast::NodeId;
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use crate::utils::{in_macro, match_def_path, match_trait_method, same_tys, snippet, span_lint_and_then};
use crate::utils::{opt_def_id, paths, resolve_node};
/// **What it does:** Checks for always-identical `Into`/`From` conversions.
///
/// **Why is this bad?** Redundant code.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// // format!() returns a `String`
/// let s: String = format!("hello").into();
/// ```
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declare_clippy_lint! {
pub IDENTITY_CONVERSION,
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complexity,
"using always-identical `Into`/`From` conversions"
}
#[derive(Default)]
pub struct IdentityConversion {
try_desugar_arm: Vec<NodeId>,
}
impl LintPass for IdentityConversion {
fn get_lints(&self) -> LintArray {
lint_array!(IDENTITY_CONVERSION)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if in_macro(e.span) {
return;
}
if Some(&e.id) == self.try_desugar_arm.last() {
return;
}
match e.node {
ExprMatch(_, ref arms, MatchSource::TryDesugar) => {
let e = match arms[0].body.node {
ExprRet(Some(ref e)) | ExprBreak(_, Some(ref e)) => e,
_ => return,
};
if let ExprCall(_, ref args) = e.node {
self.try_desugar_arm.push(args[0].id);
} else {
return;
}
},
ExprMethodCall(ref name, .., ref args) => {
if match_trait_method(cx, e, &paths::INTO[..]) && &*name.name.as_str() == "into" {
let a = cx.tables.expr_ty(e);
let b = cx.tables.expr_ty(&args[0]);
if same_tys(cx, a, b) {
let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
db.span_suggestion(e.span, "consider removing `.into()`", sugg);
});
}
}
},
ExprCall(ref path, ref args) => if let ExprPath(ref qpath) = path.node {
if let Some(def_id) = opt_def_id(resolve_node(cx, qpath, path.hir_id)) {
if match_def_path(cx.tcx, def_id, &paths::FROM_FROM[..]) {
let a = cx.tables.expr_ty(e);
let b = cx.tables.expr_ty(&args[0]);
if same_tys(cx, a, b) {
let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
let sugg_msg = format!("consider removing `{}()`", snippet(cx, path.span, "From::from"));
span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
db.span_suggestion(e.span, &sugg_msg, sugg);
});
}
}
}
},
_ => {},
}
}
fn check_expr_post(&mut self, _: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if Some(&e.id) == self.try_desugar_arm.last() {
self.try_desugar_arm.pop();
}
}
}