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Fix useless_format false negative

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Closes #2546
This commit is contained in:
Michael Wright 2018-04-12 08:21:03 +02:00
parent c067bc3cd0
commit 6ae617b313
3 changed files with 105 additions and 19 deletions
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62
clippy_lints/src/format.rs
View file

@ -2,8 +2,9 @@ use rustc::hir::*;
use rustc::lint::*;
use rustc::ty;
use syntax::ast::LitKind;
use syntax_pos::Span;
use utils::paths;
use utils::{in_macro, is_expn_of, match_def_path, match_type, opt_def_id, resolve_node, snippet, span_lint_and_then, walk_ptrs_ty};
use 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.
@ -43,20 +44,19 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
return;
}
match expr.node {
// `format!("{}", foo)` expansion
ExprCall(ref fun, ref args) => {
if_chain! {
if let ExprPath(ref qpath) = fun.node;
if args.len() == 2;
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_NEWV1);
// ensure the format string is `"{..}"` with only one argument and no text
if check_static_str(&args[0]);
// ensure the format argument is `{}` ie. Display with no fancy option
// and that the argument is a string
if check_arg_is_display(cx, &args[1]);
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, expr.span, "<expr>").into_owned());
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);
});
@ -79,7 +79,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
}
/// Checks if the expressions matches `&[""]`
fn check_static_str(expr: &Expr) -> bool {
fn check_single_piece(expr: &Expr) -> bool {
if_chain! {
if let ExprAddrOf(_, ref expr) = expr.node; // &[""]
if let ExprArray(ref exprs) = expr.node; // [""]
@ -96,15 +96,17 @@ fn check_static_str(expr: &Expr) -> bool {
/// Checks if the expressions matches
/// ```rust,ignore
/// &match (&42,) {
/// &match (&"arg",) {
/// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
/// ::std::fmt::Display::fmt)],
/// }
/// ```
fn check_arg_is_display(cx: &LateContext, expr: &Expr) -> bool {
/// 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 ExprAddrOf(_, ref expr) = expr.node;
if let ExprMatch(_, ref arms, _) = expr.node;
if let ExprMatch(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;
@ -118,8 +120,40 @@ fn check_arg_is_display(cx: &LateContext, expr: &Expr) -> bool {
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 ExprTup(ref values) = match_expr.node {
return Some(values[0].span);
}
}
}
}
return ty.sty == ty::TyStr || match_type(cx, ty, &paths::STRING);
None
}
/// Checks if the expression matches
/// ```rust,ignore
/// &[_ {
/// format: _ {
/// width: _::Implied,
/// ...
/// },
/// ...,
/// }]
/// ```
fn check_unformatted(expr: &Expr) -> bool {
if_chain! {
if let ExprAddrOf(_, ref expr) = expr.node;
if let ExprArray(ref exprs) = expr.node;
if exprs.len() == 1;
if let ExprStruct(_, ref fields, _) = exprs[0].node;
if let Some(format_field) = fields.iter().filter(|f| f.name.node == "format").next();
if let ExprStruct(_, ref fields, _) = format_field.expr.node;
if let Some(align_field) = fields.iter().filter(|f| f.name.node == "width").next();
if let ExprPath(ref qpath) = align_field.expr.node;
if last_path_segment(qpath).name == "Implied";
then {
return true;
}
}

12
tests/ui/format.rs
View file

@ -12,15 +12,19 @@ fn main() {
format!("foo");
format!("{}", "foo");
format!("{:?}", "foo"); // we only want to warn about `{}`
format!("{:+}", "foo"); // we only want to warn about `{}`
format!("{:?}", "foo"); // don't warn about debug
format!("{:8}", "foo");
format!("{:+}", "foo"); // warn when the format makes no difference
format!("{:<}", "foo"); // warn when the format makes no difference
format!("foo {}", "bar");
format!("{} bar", "foo");
let arg: String = "".to_owned();
format!("{}", arg);
format!("{:?}", arg); // we only want to warn about `{}`
format!("{:+}", arg); // we only want to warn about `{}`
format!("{:?}", arg); // don't warn about debug
format!("{:8}", arg);
format!("{:+}", arg); // warn when the format makes no difference
format!("{:<}", arg); // warn when the format makes no difference
format!("foo {}", arg);
format!("{} bar", arg);

50
tests/ui/format.stderr
View file

@ -6,5 +6,53 @@ error: useless use of `format!`
|
= note: `-D useless-format` implied by `-D warnings`
error: aborting due to previous error
error: useless use of `format!`
--> $DIR/format.rs:14:5
|
14 | format!("{}", "foo");
| ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: useless use of `format!`
--> $DIR/format.rs:17:5
|
17 | format!("{:+}", "foo"); // warn when the format makes no difference
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: useless use of `format!`
--> $DIR/format.rs:18:5
|
18 | format!("{:<}", "foo"); // warn when the format makes no difference
| ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: useless use of `format!`
--> $DIR/format.rs:23:5
|
23 | format!("{}", arg);
| ^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: useless use of `format!`
--> $DIR/format.rs:26:5
|
26 | format!("{:+}", arg); // warn when the format makes no difference
| ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: useless use of `format!`
--> $DIR/format.rs:27:5
|
27 | format!("{:<}", arg); // warn when the format makes no difference
| ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
|
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
error: aborting due to 7 previous errors