rust-clippy/clippy_lints/src/format.rs
Oliver Schneider afd91248ed Rustup
2018-07-23 13:01:12 +02:00

163 lines
5.9 KiB
Rust

use rustc::hir::*;
use rustc::lint::*;
use rustc::{declare_lint, lint_array};
use if_chain::if_chain;
use rustc::ty;
use syntax::ast::LitKind;
use syntax_pos::Span;
use crate::utils::paths;
use crate::utils::{in_macro, is_expn_of, last_path_segment, match_def_path, match_type, opt_def_id, resolve_node, snippet, span_lint_and_then, walk_ptrs_ty};
/// **What it does:** Checks for the use of `format!("string literal with no
/// argument")` and `format!("{}", foo)` where `foo` is a string.
///
/// **Why is this bad?** There is no point of doing that. `format!("too")` can
/// be replaced by `"foo".to_owned()` if you really need a `String`. The even
/// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
/// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
/// if `foo: &str`.
///
/// **Known problems:** None.
///
/// **Examples:**
/// ```rust
/// format!("foo")
/// format!("{}", foo)
/// ```
declare_clippy_lint! {
pub USELESS_FORMAT,
complexity,
"useless use of `format!`"
}
#[derive(Copy, Clone, Debug)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array![USELESS_FORMAT]
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let Some(span) = is_expn_of(expr.span, "format") {
if in_macro(span) {
return;
}
match expr.node {
// `format!("{}", foo)` expansion
ExprKind::Call(ref fun, ref args) => {
if_chain! {
if let ExprKind::Path(ref qpath) = fun.node;
if args.len() == 3;
if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, fun.hir_id));
if match_def_path(cx.tcx, fun_def_id, &paths::FMT_ARGUMENTS_NEWV1FORMATTED);
if check_single_piece(&args[0]);
if let Some(format_arg) = get_single_string_arg(cx, &args[1]);
if check_unformatted(&args[2]);
then {
let sugg = format!("{}.to_string()", snippet(cx, format_arg, "<arg>").into_owned());
span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
db.span_suggestion(expr.span, "consider using .to_string()", sugg);
});
}
}
},
// `format!("foo")` expansion contains `match () { () => [], }`
ExprKind::Match(ref matchee, _, _) => if let ExprKind::Tup(ref tup) = matchee.node {
if tup.is_empty() {
let sugg = format!("{}.to_string()", snippet(cx, expr.span, "<expr>").into_owned());
span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
db.span_suggestion(span, "consider using .to_string()", sugg);
});
}
},
_ => (),
}
}
}
}
/// Checks if the expressions matches `&[""]`
fn check_single_piece(expr: &Expr) -> bool {
if_chain! {
if let ExprKind::AddrOf(_, ref expr) = expr.node; // &[""]
if let ExprKind::Array(ref exprs) = expr.node; // [""]
if exprs.len() == 1;
if let ExprKind::Lit(ref lit) = exprs[0].node;
if let LitKind::Str(ref lit, _) = lit.node;
then {
return lit.as_str().is_empty();
}
}
false
}
/// Checks if the expressions matches
/// ```rust,ignore
/// &match (&"arg",) {
/// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
/// ::std::fmt::Display::fmt)],
/// }
/// ```
/// and that type of `__arg0` is `&str` or `String`
/// then returns the span of first element of the matched tuple
fn get_single_string_arg(cx: &LateContext<'_, '_>, expr: &Expr) -> Option<Span> {
if_chain! {
if let ExprKind::AddrOf(_, ref expr) = expr.node;
if let ExprKind::Match(ref match_expr, ref arms, _) = expr.node;
if arms.len() == 1;
if arms[0].pats.len() == 1;
if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node;
if pat.len() == 1;
if let ExprKind::Array(ref exprs) = arms[0].body.node;
if exprs.len() == 1;
if let ExprKind::Call(_, ref args) = exprs[0].node;
if args.len() == 2;
if let ExprKind::Path(ref qpath) = args[1].node;
if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, args[1].hir_id));
if match_def_path(cx.tcx, fun_def_id, &paths::DISPLAY_FMT_METHOD);
then {
let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
if ty.sty == ty::TyStr || match_type(cx, ty, &paths::STRING) {
if let ExprKind::Tup(ref values) = match_expr.node {
return Some(values[0].span);
}
}
}
}
None
}
/// Checks if the expression matches
/// ```rust,ignore
/// &[_ {
/// format: _ {
/// width: _::Implied,
/// ...
/// },
/// ...,
/// }]
/// ```
fn check_unformatted(expr: &Expr) -> bool {
if_chain! {
if let ExprKind::AddrOf(_, ref expr) = expr.node;
if let ExprKind::Array(ref exprs) = expr.node;
if exprs.len() == 1;
if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
if let Some(format_field) = fields.iter().find(|f| f.ident.name == "format");
if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node;
if let Some(align_field) = fields.iter().find(|f| f.ident.name == "width");
if let ExprKind::Path(ref qpath) = align_field.expr.node;
if last_path_segment(qpath).ident.name == "Implied";
then {
return true;
}
}
false
}