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matthiaskrgrmatthiaskrgr
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Rollup merge of rust-lang#146123 - IoaNNUwU:issue-68293, r=estebank
Suggest examples of format specifiers in error messages Format macro now suggests adding `{}` if no formatting specifiers are present. It also gives an example: ```rust 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"); | ++ ``` When one or more `{}` are present, it doesn't show 'format specifiers use curly braces: `{}`' and example, just small hint on how many you missing: ```rust LL | println!("list: {}", 1, 2, 3); | ---------- ^ ^ argument never used | | | | | argument never used | multiple missing formatting specifiers | = help: consider adding 2 format specifiers ``` Original issue: rust-lang#68293 Based on discussion in this PR: rust-lang#76443 Let me know if something is missing
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‎compiler/rustc_builtin_macros/src/format.rs‎

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Original file line numberDiff line numberDiff line change
@@ -565,6 +565,7 @@ fn make_format_args(
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&used,
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&args,
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&pieces,
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&invalid_refs,
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detect_foreign_fmt,
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str_style,
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fmt_str,
@@ -645,6 +646,7 @@ fn report_missing_placeholders(
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used: &[bool],
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args: &FormatArguments,
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pieces: &[parse::Piece<'_>],
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invalid_refs: &[(usize, Option<Span>, PositionUsedAs, FormatArgPositionKind)],
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detect_foreign_fmt: bool,
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str_style: Option<usize>,
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fmt_str: &str,
@@ -762,6 +764,31 @@ fn report_missing_placeholders(
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diag.span_label(fmt_span, "formatting specifier missing");
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}
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if !found_foreign && invalid_refs.is_empty() {
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// Show example if user didn't use any format specifiers
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let show_example = used.iter().all(|used| !used);
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if !show_example {
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if unused.len() > 1 {
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diag.note(format!("consider adding {} format specifiers", unused.len()));
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}
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} else {
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let original_fmt_str =
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if fmt_str.len() >= 1 { &fmt_str[..fmt_str.len() - 1] } else { "" };
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let msg = if unused.len() == 1 {
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"a format specifier".to_string()
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} else {
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format!("{} format specifiers", unused.len())
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};
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let sugg = format!("\"{}{}\"", original_fmt_str, "{}".repeat(unused.len()));
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let msg = format!("format specifiers use curly braces, consider adding {msg}");
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diag.span_suggestion_verbose(fmt_span, msg, sugg, Applicability::MaybeIncorrect);
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}
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}
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diag.emit();
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}
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‎tests/ui/fmt/ifmt-bad-arg.stderr‎

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Original file line numberDiff line numberDiff line change
@@ -62,6 +62,11 @@ LL | format!("", 1, 2);
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| | |
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| | argument never used
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| multiple missing formatting specifiers
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|
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help: format specifiers use curly braces, consider adding 2 format specifiers
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|
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LL | format!("{}{}", 1, 2);
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| ++++
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error: argument never used
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--> $DIR/ifmt-bad-arg.rs:33:22
@@ -102,6 +107,11 @@ LL | format!("", foo=2);
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| -- ^ named argument never used
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| |
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| formatting specifier missing
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|
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help: format specifiers use curly braces, consider adding a format specifier
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|
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LL | format!("{}", foo=2);
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| ++
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error: multiple unused formatting arguments
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--> $DIR/ifmt-bad-arg.rs:38:32
@@ -111,6 +121,8 @@ LL | format!("{} {}", 1, 2, foo=1, bar=2);
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| | |
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| | named argument never used
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| multiple missing formatting specifiers
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|
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= note: consider adding 2 format specifiers
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error: duplicate argument named `foo`
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--> $DIR/ifmt-bad-arg.rs:40:29

‎tests/ui/macros/format-unused-lables.stderr‎

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Original file line numberDiff line numberDiff line change
@@ -7,6 +7,11 @@ LL | println!("Test", 123, 456, 789);
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| | | argument never used
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| | argument never used
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| multiple missing formatting specifiers
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|
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help: format specifiers use curly braces, consider adding 3 format specifiers
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|
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LL | println!("Test{}{}{}", 123, 456, 789);
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| ++++++
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error: multiple unused formatting arguments
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--> $DIR/format-unused-lables.rs:6:9
@@ -19,6 +24,11 @@ LL | 456,
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| ^^^ argument never used
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LL | 789
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| ^^^ argument never used
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|
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help: format specifiers use curly braces, consider adding 3 format specifiers
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|
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LL | println!("Test2{}{}{}",
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| ++++++
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error: named argument never used
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--> $DIR/format-unused-lables.rs:11:35
@@ -27,6 +37,11 @@ LL | println!("Some stuff", UNUSED="args");
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| ------------ ^^^^^^ named argument never used
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| |
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| formatting specifier missing
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|
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help: format specifiers use curly braces, consider adding a format specifier
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|
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LL | println!("Some stuff{}", UNUSED="args");
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| ++
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error: multiple unused formatting arguments
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--> $DIR/format-unused-lables.rs:14:9

‎tests/ui/mir/unsized-extern-static.stderr‎

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@@ -5,6 +5,11 @@ LL | println!("C", unsafe { &symbol });
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| --- ^^^^^^^^^^^^^^^^^^ argument never used
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| |
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| formatting specifier missing
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|
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help: format specifiers use curly braces, consider adding a format specifier
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|
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LL | println!("C{}", unsafe { &symbol });
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| ++
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error[E0277]: the size for values of type `[i8]` cannot be known at compilation time
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--> $DIR/unsized-extern-static.rs:6:5

‎tests/ui/suggestions/missing-format-specifiers-issue-68293.rs‎

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@@ -0,0 +1,35 @@
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fn no_format_specifier_two_unused_args() {
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println!("Hello", "World");
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//~^ ERROR argument never used
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//~| NOTE formatting specifier missing
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//~| NOTE argument never used
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//~| HELP format specifiers use curly braces, consider adding a format specifier
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}
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fn no_format_specifier_multiple_unused_args() {
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println!("list: ", 1, 2, 3);
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//~^ ERROR multiple unused formatting arguments
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//~| NOTE multiple missing formatting specifiers
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//~| NOTE argument never used
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//~| NOTE argument never used
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//~| NOTE argument never used
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//~| HELP format specifiers use curly braces, consider adding 3 format specifiers
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}
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fn missing_format_specifiers_one_unused_arg() {
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println!("list: {}, {}", 1, 2, 3);
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//~^ ERROR argument never used
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//~| NOTE formatting specifier missing
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//~| NOTE argument never used
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}
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fn missing_format_specifiers_multiple_unused_args() {
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println!("list: {}", 1, 2, 3);
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//~^ ERROR multiple unused formatting arguments
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//~| NOTE multiple missing formatting specifiers
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//~| NOTE argument never used
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//~| NOTE argument never used
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//~| NOTE consider adding 2 format specifiers
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}
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fn main() { }

‎tests/ui/suggestions/missing-format-specifiers-issue-68293.stderr‎

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@@ -0,0 +1,49 @@
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error: argument never used
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--> $DIR/missing-format-specifiers-issue-68293.rs:2:23
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|
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LL | println!("Hello", "World");
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| ------- ^^^^^^^ argument never used
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| |
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| formatting specifier missing
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|
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help: format specifiers use curly braces, consider adding a format specifier
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|
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LL | println!("Hello{}", "World");
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| ++
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error: multiple unused formatting arguments
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--> $DIR/missing-format-specifiers-issue-68293.rs:10:24
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|
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LL | println!("list: ", 1, 2, 3);
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| -------- ^ ^ ^ argument never used
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| | | |
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| | | argument never used
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| | argument never used
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| multiple missing formatting specifiers
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|
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help: format specifiers use curly braces, consider adding 3 format specifiers
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|
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LL | println!("list: {}{}{}", 1, 2, 3);
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| ++++++
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error: argument never used
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--> $DIR/missing-format-specifiers-issue-68293.rs:20:36
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|
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LL | println!("list: {}, {}", 1, 2, 3);
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| -------------- ^ argument never used
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| |
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| formatting specifier missing
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error: multiple unused formatting arguments
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--> $DIR/missing-format-specifiers-issue-68293.rs:27:29
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|
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LL | println!("list: {}", 1, 2, 3);
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| ---------- ^ ^ argument never used
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| | |
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| | argument never used
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| multiple missing formatting specifiers
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|
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= note: consider adding 2 format specifiers
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error: aborting due to 4 previous errors
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