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Suggest examples of format specifiers in error messages #146123

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41 changes: 41 additions & 0 deletions compiler/rustc_builtin_macros/src/format.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -565,6 +565,7 @@ fn make_format_args(
&used,
&args,
&pieces,
&invalid_refs,
detect_foreign_fmt,
str_style,
fmt_str,
Expand Down Expand Up @@ -645,6 +646,7 @@ fn report_missing_placeholders(
used: &[bool],
args: &FormatArguments,
pieces: &[parse::Piece<'_>],
invalid_refs: &[(usize, Option<Span>, PositionUsedAs, FormatArgPositionKind)],
detect_foreign_fmt: bool,
str_style: Option<usize>,
fmt_str: &str,
Expand Down Expand Up @@ -762,6 +764,45 @@ fn report_missing_placeholders(
diag.span_label(fmt_span, "formatting specifier missing");
}

if !found_foreign && invalid_refs.is_empty() {
// Show example if user didn't use any format specifiers
let show_example = used.iter().all(|used| !used);

if !show_example && unused.len() > 1 {
diag.note(format!("consider adding {} format specifiers", unused.len()));
}

let original_fmt_str = if fmt_str.len() >= 1 { &fmt_str[..fmt_str.len() - 1] } else { "" };

if show_example && unused.len() == 1 {
diag.note("format specifiers use curly braces: `{}`");

diag.span_suggestion_verbose(
fmt_span,
"consider adding format specifier",
format!("\"{}{{}}\"", original_fmt_str),
Applicability::MaybeIncorrect,
);
}

if show_example && unused.len() > 1 {
diag.note("format specifiers use curly braces: `{}`");

let mut suggest_fixed_fmt = format!("\"{}", original_fmt_str);
for _ in &unused {
suggest_fixed_fmt.push_str("{}");
}
suggest_fixed_fmt.push('"');

diag.span_suggestion_verbose(
fmt_span,
format!("consider adding {} format specifiers", unused.len()),
suggest_fixed_fmt,
Applicability::MaybeIncorrect,
);
}
}

diag.emit();
}

Expand Down
14 changes: 14 additions & 0 deletions tests/ui/fmt/ifmt-bad-arg.stderr
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,12 @@ LL | format!("", 1, 2);
| | |
| | argument never used
| multiple missing formatting specifiers
|
= note: format specifiers use curly braces: `{}`
help: consider adding 2 format specifiers
|
LL | format!("{}{}", 1, 2);
| ++++

error: argument never used
--> $DIR/ifmt-bad-arg.rs:33:22
Expand Down Expand Up @@ -102,6 +108,12 @@ LL | format!("", foo=2);
| -- ^ named argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`
help: consider adding format specifier
|
LL | format!("{}", foo=2);
| ++

error: multiple unused formatting arguments
--> $DIR/ifmt-bad-arg.rs:38:32
Expand All @@ -111,6 +123,8 @@ LL | format!("{} {}", 1, 2, foo=1, bar=2);
| | |
| | named argument never used
| multiple missing formatting specifiers
|
= note: consider adding 2 format specifiers

error: duplicate argument named `foo`
--> $DIR/ifmt-bad-arg.rs:40:29
Expand Down
18 changes: 18 additions & 0 deletions tests/ui/macros/format-unused-lables.stderr
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,12 @@ LL | println!("Test", 123, 456, 789);
| | | argument never used
| | argument never used
| multiple missing formatting specifiers
|
= note: format specifiers use curly braces: `{}`
help: consider adding 3 format specifiers
|
LL | println!("Test{}{}{}", 123, 456, 789);
| ++++++

error: multiple unused formatting arguments
--> $DIR/format-unused-lables.rs:6:9
Expand All @@ -19,6 +25,12 @@ LL | 456,
| ^^^ argument never used
LL | 789
| ^^^ argument never used
|
= note: format specifiers use curly braces: `{}`
help: consider adding 3 format specifiers
|
LL | println!("Test2{}{}{}",
| ++++++

error: named argument never used
--> $DIR/format-unused-lables.rs:11:35
Expand All @@ -27,6 +39,12 @@ LL | println!("Some stuff", UNUSED="args");
| ------------ ^^^^^^ named argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`
help: consider adding format specifier
|
LL | println!("Some stuff{}", UNUSED="args");
| ++

error: multiple unused formatting arguments
--> $DIR/format-unused-lables.rs:14:9
Expand Down
6 changes: 6 additions & 0 deletions tests/ui/mir/unsized-extern-static.stderr
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,12 @@ LL | println!("C", unsafe { &symbol });
| --- ^^^^^^^^^^^^^^^^^^ argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`
help: consider adding format specifier
|
LL | println!("C{}", unsafe { &symbol });
| ++

error[E0277]: the size for values of type `[i8]` cannot be known at compilation time
--> $DIR/unsized-extern-static.rs:6:5
Expand Down
35 changes: 35 additions & 0 deletions tests/ui/suggestions/missing-format-specifiers-issue-68293.rs
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
fn no_format_specifier_two_unused_args() {
println!("Hello", "World");
//~^ ERROR argument never used
//~| NOTE formatting specifier missing
//~| NOTE format specifiers use curly braces: `{}`
//~| NOTE argument never used
}

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

fn missing_format_specifiers_multiple_unused_args() {
println!("list: {}", 1, 2, 3);
//~^ ERROR multiple unused formatting arguments
//~| NOTE multiple missing formatting specifiers
//~| NOTE argument never used
//~| NOTE argument never used
//~| NOTE consider adding 2 format specifiers
}

fn main() { }
51 changes: 51 additions & 0 deletions tests/ui/suggestions/missing-format-specifiers-issue-68293.stderr
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,51 @@
error: argument never used
--> $DIR/missing-format-specifiers-issue-68293.rs:2:23
|
LL | println!("Hello", "World");
| ------- ^^^^^^^ argument never used
| |
| formatting specifier missing
|
= note: format specifiers use curly braces: `{}`
help: consider adding format specifier
|
LL | println!("Hello{}", "World");
| ++

error: multiple unused formatting arguments
--> $DIR/missing-format-specifiers-issue-68293.rs:10:24
|
LL | println!("list: ", 1, 2, 3);
| -------- ^ ^ ^ argument never used
| | | |
| | | argument never used
| | argument never used
| multiple missing formatting specifiers
|
= note: format specifiers use curly braces: `{}`
help: consider adding 3 format specifiers
|
LL | println!("list: {}{}{}", 1, 2, 3);
| ++++++

error: argument never used
--> $DIR/missing-format-specifiers-issue-68293.rs:20:36
|
LL | println!("list: {}, {}", 1, 2, 3);
| -------------- ^ argument never used
| |
| formatting specifier missing

error: multiple unused formatting arguments
--> $DIR/missing-format-specifiers-issue-68293.rs:27:29
|
LL | println!("list: {}", 1, 2, 3);
| ---------- ^ ^ argument never used
| | |
| | argument never used
| multiple missing formatting specifiers
|
= note: consider adding 2 format specifiers

error: aborting due to 4 previous errors

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