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Limit USELESS_FORMAT with args to string args

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mcarton 2016-02-22 17:54:46 +01:00
parent 0e9ced5cb8
commit 2a0fb1fb44
2 changed files with 37 additions and 12 deletions
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24
src/format.rs
View file

@ -1,16 +1,17 @@
use rustc::front::map::Node::NodeItem;
use rustc::lint::*;
use rustc::middle::ty::TypeVariants;
use rustc_front::hir::*;
use syntax::ast::LitKind;
use utils::{DISPLAY_FMT_METHOD_PATH, FMT_ARGUMENTS_NEWV1_PATH};
use utils::{is_expn_of, match_path, span_lint};
use utils::{DISPLAY_FMT_METHOD_PATH, FMT_ARGUMENTS_NEWV1_PATH, STRING_PATH};
use utils::{is_expn_of, match_path, match_type, span_lint, walk_ptrs_ty};
/// **What it does:** This lints about use of `format!("string literal with no argument")` and
/// `format!("{}", foo)`.
/// `format!("{}", foo)` where `foo` is a string.
///
/// **Why is this bad?** There is no point of doing that. If you want a `String` you can use
/// `to_owned` on the string literal or expression. The even worse `&format!("foo")` is often
/// encountered in the wild.
/// **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()` is `foo: &str`.
///
/// **Known problems:** None.
///
@ -43,7 +44,7 @@ impl LateLintPass for FormatMacLint {
// ensure the format string is `"{..}"` with only one argument and no text
check_static_str(cx, &args[0]),
// ensure the format argument is `{}` ie. Display with no fancy option
check_arg_is_display(&args[1])
check_arg_is_display(cx, &args[1])
], {
span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
}}
@ -94,11 +95,14 @@ fn check_static_str(cx: &LateContext, expr: &Expr) -> bool {
/// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0, ::std::fmt::Display::fmt)],
/// })
/// ```
fn check_arg_is_display(expr: &Expr) -> bool {
fn check_arg_is_display(cx: &LateContext, expr: &Expr) -> bool {
if_let_chain! {[
let ExprAddrOf(_, ref expr) = expr.node,
let ExprMatch(_, ref arms, _) = expr.node,
arms.len() == 1,
arms[0].pats.len() == 1,
let PatKind::Tup(ref pat) = arms[0].pats[0].node,
pat.len() == 1,
let ExprVec(ref exprs) = arms[0].body.node,
exprs.len() == 1,
let ExprCall(_, ref args) = exprs[0].node,
@ -106,7 +110,9 @@ fn check_arg_is_display(expr: &Expr) -> bool {
let ExprPath(None, ref path) = args[1].node,
match_path(path, &DISPLAY_FMT_METHOD_PATH)
], {
return true;
let ty = walk_ptrs_ty(cx.tcx.pat_ty(&pat[0]));
return ty.sty == TypeVariants::TyStr || match_type(cx, ty, &STRING_PATH);
}}
false

25
tests/compile-fail/format.rs
View file

@ -4,12 +4,31 @@
fn main() {
format!("foo"); //~ERROR useless use of `format!`
format!("{}", 42); //~ERROR useless use of `format!`
format!("{:?}", 42); // we only want to warn about `{}`
format!("{:+}", 42); // we only want to warn about `{}`
format!("{}", "foo"); //~ERROR useless use of `format!`
format!("{:?}", "foo"); // we only want to warn about `{}`
format!("{:+}", "foo"); // we only want to warn about `{}`
format!("foo {}", "bar");
format!("{} bar", "foo");
let arg: String = "".to_owned();
format!("{}", arg); //~ERROR useless use of `format!`
format!("{:?}", arg); // we only want to warn about `{}`
format!("{:+}", arg); // we only want to warn about `{}`
format!("foo {}", arg);
format!("{} bar", arg);
// we don’t want to warn for non-string args, see #697
format!("{}", 42);
format!("{:?}", 42);
format!("{:+}", 42);
format!("foo {}", 42);
format!("{} bar", 42);
// we only want to warn about `format!` itself
println!("foo");
println!("{}", "foo");
println!("foo {}", "foo");
println!("{}", 42);
println!("foo {}", 42);
}