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Add format specifier suggestion #76443

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53 changes: 47 additions & 6 deletions compiler/rustc_builtin_macros/src/format.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1090,20 +1090,21 @@ pub fn expand_preparsed_format_args(
if !errs.is_empty() {
let args_used = cx.arg_types.len() - errs_len;
let args_unused = errs_len;
let found_fmt_specs = &cx.arg_spans;

let mut diag = {
if let [(sp, msg)] = &errs[..] {
let mut diag = cx.ecx.struct_span_err(*sp, *msg);
diag.span_label(*sp, *msg);
diag
} else {
let mut diag = cx.ecx.struct_span_err(
errs.iter().map(|&(sp, _)| sp).collect::<Vec<Span>>(),
"multiple unused formatting arguments",
);
let mut diag = cx
.ecx
.struct_span_err(errs.iter().map(|&(sp, _)| sp).collect::<Vec<Span>>(),
"multiple unused formatting arguments");
diag.span_label(cx.fmtsp, "multiple missing formatting specifiers");
for (sp, msg) in errs {
diag.span_label(sp, msg);
for (sp, msg) in &errs {
diag.span_label(*sp, *msg);
}
diag
}
Expand Down Expand Up @@ -1178,6 +1179,46 @@ pub fn expand_preparsed_format_args(
if !found_foreign && errs_len == 1 {
diag.span_label(cx.fmtsp, "formatting specifier missing");
}
if !found_foreign && found_fmt_specs.is_empty() {
diag.note("format specifiers use curly braces: `{}`");
}

if !found_foreign && !found_fmt_specs.is_empty() {
let mut note_span: MultiSpan = cx.arg_spans.clone().into();
let used_args = cx
.arg_types
.iter()
.enumerate()
.filter(|(_i, ty)| !ty.is_empty())
.map(|(i, _)| {
(cx.args[i].span, i)
})
.collect::<Vec<_>>();

let names_reversed: FxHashMap<usize, Symbol> = cx.names.iter().map(|(symbol, pos)| {
(*pos, *symbol)
}).collect();

for (span, index) in &used_args {
let mut fmt_arg_type = "positional";
let mut fmt_arg_ident = (*index).to_string();

if let Some(&symbol) = names_reversed.get(index) {
fmt_arg_type = "named";
fmt_arg_ident = symbol.to_ident_string();
}

note_span.push_span_label(*span, format!("used {} formatting argument `{}`", fmt_arg_type, fmt_arg_ident));

// for each reference to a formatting argument(identified by index), get the span of its formatting specifier
// for &ref in &cx.arg_index_map[*index] {
// let sp = &cx.arg_spans[ref];
// note_span.push_span_label(*sp, format!("{} argument `{}` used here: ",fmt_arg_type, fmt_arg_ident));
// }
}

diag.span_note(note_span, "the following existing formatting specifiers are used");
}

diag.emit();
}
Expand Down
4 changes: 2 additions & 2 deletions src/test/ui/fmt/format-args-capture-missing-variables.stderr
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Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
error: named argument never used
--> $DIR/format-args-capture-missing-variables.rs:10:51
--> $DIR/format-args-capture-missing-variables.rs:10:14
|
LL | format!("{valuea} {valueb}", valuea=5, valuec=7);
| ------------------- ^ named argument never used
| -^^^^^^^^-^^^^^^^^- ^ named argument never used
| |
| formatting specifier missing

Expand Down
32 changes: 18 additions & 14 deletions src/test/ui/if/ifmt-bad-arg.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -13,10 +13,10 @@ LL | format!("{1}", 1);
= note: positional arguments are zero-based

error: argument never used
--> $DIR/ifmt-bad-arg.rs:9:20
--> $DIR/ifmt-bad-arg.rs:9:14
|
LL | format!("{1}", 1);
| ----- ^ argument never used
| -^^^- ^ argument never used
| |
| formatting specifier missing

Expand Down Expand Up @@ -90,36 +90,38 @@ LL | format!("", 1, 2);
| | |
| | argument never used
| multiple missing formatting specifiers
|
= note: format specifiers use curly braces: `{}`

error: argument never used
--> $DIR/ifmt-bad-arg.rs:33:22
--> $DIR/ifmt-bad-arg.rs:33:14
|
LL | format!("{}", 1, 2);
| ---- ^ argument never used
| -^^- ^ argument never used
| |
| formatting specifier missing
Comment on lines 96 to 102
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I think that ideally this would look like

error: argument never used
  --> $DIR/ifmt-bad-arg.rs:33:22
   |
LL |     format!("{}", 1, 2);
   |             ----     ^ argument never used
   |             |
   |             formatting specifier missing
note: the following existing formatting specifiers are used
   |
LL |     format!("{}", 1, 2);
   |              ^^      - used by positional formatting specifier `0`
   |              |
   |              this is positional formatting specifier `0`

In order to accomplish that we would need to

  • keep track of the spans for each formatting specifier and a way to refer to them ("positional specifier 0", "named specifier foo", etc.)
  • look at the mapping for which formatting specifier is used by which argument
  • we'll need to account for named and positional specifiers that are not used

For the proposed output we would need to do something like (simplified):

let note_span: MultiSpan = cx.arg_spans.into();
for span in cx.arg_spans {
    note_span.push_span_label(span, "used argument");
}
for span in errs.iter().map(|&(sp, _)| sp) {
  note_span.push_span_label(span, "argument used here");
}
err.span_note(note_span, "the following existing formatting specifiers are used");

Would you be ok with taking on trying to accomplish this?

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yup, I'll work on making these changes. Thanks for the feedback!


error: argument never used
--> $DIR/ifmt-bad-arg.rs:34:20
--> $DIR/ifmt-bad-arg.rs:34:14
|
LL | format!("{1}", 1, 2);
| ----- ^ argument never used
| -^^^- ^ argument never used
| |
| formatting specifier missing

error: named argument never used
--> $DIR/ifmt-bad-arg.rs:35:26
--> $DIR/ifmt-bad-arg.rs:35:14
|
LL | format!("{}", 1, foo=2);
| ---- ^ named argument never used
| -^^- ^ named argument never used
| |
| formatting specifier missing

error: argument never used
--> $DIR/ifmt-bad-arg.rs:36:22
--> $DIR/ifmt-bad-arg.rs:36:14
|
LL | format!("{foo}", 1, foo=2);
| ------- ^ argument never used
| -^^^^^- ^ argument never used
| |
| formatting specifier missing

Expand All @@ -130,12 +132,14 @@ LL | format!("", foo=2);
| -- ^ named argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`

error: multiple unused formatting arguments
--> $DIR/ifmt-bad-arg.rs:38:32
--> $DIR/ifmt-bad-arg.rs:38:14
|
LL | format!("{} {}", 1, 2, foo=1, bar=2);
| ------- ^ ^ named argument never used
| -^^-^^- ^ ^ named argument never used
| | |
| | named argument never used
| multiple missing formatting specifiers
Expand Down Expand Up @@ -165,10 +169,10 @@ LL | format!("{valuea} {valueb}", valuea=5, valuec=7);
= help: if you intended to capture `valueb` from the surrounding scope, add `#![feature(format_args_capture)]` to the crate attributes

error: named argument never used
--> $DIR/ifmt-bad-arg.rs:45:51
--> $DIR/ifmt-bad-arg.rs:45:14
|
LL | format!("{valuea} {valueb}", valuea=5, valuec=7);
| ------------------- ^ named argument never used
| -^^^^^^^^-^^^^^^^^- ^ named argument never used
| |
| formatting specifier missing

Expand Down
4 changes: 2 additions & 2 deletions src/test/ui/macros/format-foreign.stderr
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Expand Up @@ -45,10 +45,10 @@ LL | {}!\n
|

error: argument never used
--> $DIR/format-foreign.rs:12:30
--> $DIR/format-foreign.rs:12:15
|
LL | println!("{} %f", "one", 2.0);
| ------- ^^^ argument never used
| -^^---- ^^^ argument never used
| |
| formatting specifier missing

Expand Down
6 changes: 6 additions & 0 deletions src/test/ui/macros/format-unused-lables.stderr
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Expand Up @@ -7,6 +7,8 @@ LL | println!("Test", 123, 456, 789);
| | | argument never used
| | argument never used
| multiple missing formatting specifiers
|
= note: format specifiers use curly braces: `{}`

error: multiple unused formatting arguments
--> $DIR/format-unused-lables.rs:6:9
Expand All @@ -19,6 +21,8 @@ LL | 456,
| ^^^ argument never used
LL | 789
| ^^^ argument never used
|
= note: format specifiers use curly braces: `{}`

error: named argument never used
--> $DIR/format-unused-lables.rs:11:35
Expand All @@ -27,6 +31,8 @@ LL | println!("Some stuff", UNUSED="args");
| ------------ ^^^^^^ named argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`

error: multiple unused formatting arguments
--> $DIR/format-unused-lables.rs:14:9
Expand Down
38 changes: 38 additions & 0 deletions src/test/ui/suggestions/issue-68293-missing-format-specifier.rs
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@@ -0,0 +1,38 @@
// Issue 68293: This tests that the following changes work:
// the suggestion "format specifiers use curly braces: `{}`" is made
// found format specifiers are pointed at

fn no_format_specifiers_one_unused_argument() {
println!("list: ", 1);
//~^ ERROR argument never used
//~| NOTE formatting specifier missing
//~| NOTE format specifiers use curly braces: `{}`
//~| NOTE argument never used
}

fn no_format_specifiers_multiple_unused_arguments() {
println!("list: ", 3, 4, 5);
//~^ ERROR multiple unused formatting arguments
//~| NOTE multiple missing formatting specifiers
//~| NOTE format specifiers use curly braces: `{}`
//~| NOTE argument never used
//~| NOTE argument never used
//~| NOTE argument never used
}

fn missing_format_specifiers_one_unused_argument() {
println!("list: a{}, b{}", 1, 2, 3);
//~^ ERROR argument never used
//~| NOTE formatting specifier missing
//~| NOTE argument never used
}

fn missing_format_specifiers_multiple_unused_arguments() {
println!("list: a{}, b{} c{}", 1, 2, 3, 4, 5);
//~^ ERROR multiple unused formatting arguments
//~| NOTE multiple missing formatting specifiers
//~| NOTE argument never used
//~| NOTE argument never used
}

fn main() {}
41 changes: 41 additions & 0 deletions src/test/ui/suggestions/issue-68293-missing-format-specifier.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,41 @@
error: argument never used
--> $DIR/issue-68293-missing-format-specifier.rs:6:22
|
LL | println!("list: ", 1);
| -------- ^ argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`

error: multiple unused formatting arguments
--> $DIR/issue-68293-missing-format-specifier.rs:14:22
|
LL | println!("list: ", 3, 4, 5);
| -------- ^ ^ ^ argument never used
| | | |
| | | argument never used
| | argument never used
| multiple missing formatting specifiers
|
= note: format specifiers use curly braces: `{}`

error: argument never used
--> $DIR/issue-68293-missing-format-specifier.rs:24:20
|
LL | println!("list: a{}, b{}", 1, 2, 3);
| --------^^---^^- ^ argument never used
| |
| formatting specifier missing

error: multiple unused formatting arguments
--> $DIR/issue-68293-missing-format-specifier.rs:31:20
|
LL | println!("list: a{}, b{} c{}", 1, 2, 3, 4, 5);
| --------^^---^^--^^- ^ ^ argument never used
| | |
| | argument never used
| multiple missing formatting specifiers

error: aborting due to 4 previous errors