208 lines
7.6 KiB
Rust
208 lines
7.6 KiB
Rust
use crate::utils::paths;
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use crate::utils::{
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in_macro, is_expn_of, last_path_segment, match_def_path, match_type, resolve_node, snippet, span_lint_and_then,
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walk_ptrs_ty,
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};
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use if_chain::if_chain;
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use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass};
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use rustc::ty;
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use rustc::{declare_tool_lint, lint_array};
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use rustc_errors::Applicability;
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use syntax::ast::LitKind;
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use syntax::source_map::Span;
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declare_clippy_lint! {
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/// **What it does:** Checks for the use of `format!("string literal with no
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/// argument")` and `format!("{}", foo)` where `foo` is a string.
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///
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/// **Why is this bad?** There is no point of doing that. `format!("foo")` can
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/// be replaced by `"foo".to_owned()` if you really need a `String`. The even
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/// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
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/// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
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/// if `foo: &str`.
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///
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/// **Known problems:** None.
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///
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/// **Examples:**
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/// ```rust
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/// format!("foo")
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/// format!("{}", foo)
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/// ```
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pub USELESS_FORMAT,
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complexity,
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"useless use of `format!`"
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}
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#[derive(Copy, Clone, Debug)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array![USELESS_FORMAT]
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}
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fn name(&self) -> &'static str {
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"UselessFormat"
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let Some(span) = is_expn_of(expr.span, "format") {
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if in_macro(span) {
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return;
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}
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match expr.node {
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// `format!("{}", foo)` expansion
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ExprKind::Call(ref fun, ref args) => {
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if_chain! {
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if let ExprKind::Path(ref qpath) = fun.node;
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if let Some(fun_def_id) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
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let new_v1 = match_def_path(cx.tcx, fun_def_id, &paths::FMT_ARGUMENTS_NEWV1);
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let new_v1_fmt = match_def_path(
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cx.tcx,
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fun_def_id,
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&paths::FMT_ARGUMENTS_NEWV1FORMATTED
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);
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if new_v1 || new_v1_fmt;
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if check_single_piece(&args[0]);
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if let Some(format_arg) = get_single_string_arg(cx, &args[1]);
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if new_v1 || check_unformatted(&args[2]);
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if let ExprKind::AddrOf(_, ref format_arg) = format_arg.node;
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then {
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let (message, sugg) = if_chain! {
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if let ExprKind::MethodCall(ref path, _, _) = format_arg.node;
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if path.ident.as_interned_str() == "to_string";
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then {
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("`to_string()` is enough",
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snippet(cx, format_arg.span, "<arg>").to_string())
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} else {
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("consider using .to_string()",
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format!("{}.to_string()", snippet(cx, format_arg.span, "<arg>")))
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}
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};
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span_useless_format(cx, span, message, sugg);
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}
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}
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},
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// `format!("foo")` expansion contains `match () { () => [], }`
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ExprKind::Match(ref matchee, _, _) => {
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if let ExprKind::Tup(ref tup) = matchee.node {
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if tup.is_empty() {
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let sugg = format!("{}.to_string()", snippet(cx, expr.span, "<expr>").into_owned());
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span_useless_format(cx, span, "consider using .to_string()", sugg);
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}
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}
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},
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_ => (),
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}
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}
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}
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}
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fn span_useless_format<'a, 'tcx: 'a, T: LintContext<'tcx>>(cx: &'a T, span: Span, help: &str, mut sugg: String) {
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let to_replace = span.source_callsite();
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// The callsite span contains the statement semicolon for some reason.
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let snippet = snippet(cx, to_replace, "..");
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if snippet.ends_with(';') {
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sugg.push(';');
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}
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span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
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db.span_suggestion(
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to_replace,
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help,
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sugg,
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Applicability::MachineApplicable, // snippet
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);
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});
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}
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/// Checks if the expressions matches `&[""]`
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fn check_single_piece(expr: &Expr) -> bool {
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if_chain! {
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if let ExprKind::AddrOf(_, ref expr) = expr.node; // &[""]
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if let ExprKind::Array(ref exprs) = expr.node; // [""]
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if exprs.len() == 1;
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if let ExprKind::Lit(ref lit) = exprs[0].node;
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if let LitKind::Str(ref lit, _) = lit.node;
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then {
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return lit.as_str().is_empty();
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}
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}
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false
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}
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/// Checks if the expressions matches
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/// ```rust,ignore
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/// &match (&"arg",) {
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/// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
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/// ::std::fmt::Display::fmt)],
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/// }
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/// ```
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/// and that the type of `__arg0` is `&str` or `String`,
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/// then returns the span of first element of the matched tuple.
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fn get_single_string_arg<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<&'a Expr> {
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if_chain! {
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if let ExprKind::AddrOf(_, ref expr) = expr.node;
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if let ExprKind::Match(ref match_expr, ref arms, _) = expr.node;
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if arms.len() == 1;
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if arms[0].pats.len() == 1;
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if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node;
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if pat.len() == 1;
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if let ExprKind::Array(ref exprs) = arms[0].body.node;
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if exprs.len() == 1;
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if let ExprKind::Call(_, ref args) = exprs[0].node;
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if args.len() == 2;
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if let ExprKind::Path(ref qpath) = args[1].node;
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if let Some(fun_def_id) = resolve_node(cx, qpath, args[1].hir_id).opt_def_id();
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if match_def_path(cx.tcx, fun_def_id, &paths::DISPLAY_FMT_METHOD);
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then {
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let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
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if ty.sty == ty::Str || match_type(cx, ty, &paths::STRING) {
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if let ExprKind::Tup(ref values) = match_expr.node {
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return Some(&values[0]);
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}
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}
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}
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}
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None
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}
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/// Checks if the expression matches
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/// ```rust,ignore
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/// &[_ {
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/// format: _ {
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/// width: _::Implied,
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/// ...
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/// },
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/// ...,
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/// }]
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/// ```
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fn check_unformatted(expr: &Expr) -> bool {
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if_chain! {
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if let ExprKind::AddrOf(_, ref expr) = expr.node;
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if let ExprKind::Array(ref exprs) = expr.node;
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if exprs.len() == 1;
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if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
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if let Some(format_field) = fields.iter().find(|f| f.ident.name == "format");
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if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node;
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if let Some(width_field) = fields.iter().find(|f| f.ident.name == "width");
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if let ExprKind::Path(ref width_qpath) = width_field.expr.node;
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if last_path_segment(width_qpath).ident.name == "Implied";
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if let Some(precision_field) = fields.iter().find(|f| f.ident.name == "precision");
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if let ExprKind::Path(ref precision_path) = precision_field.expr.node;
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if last_path_segment(precision_path).ident.name == "Implied";
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then {
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return true;
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}
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}
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false
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}
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