Rollup merge of #93394 - m-ou-se:fix-93378, r=estebank

Don't allow {} to refer to implicit captures in format_args.

Fixes #93378

3 files changed, 41 insertions, 0 deletions

diff --git a/src/test/ui/fmt/format-args-capture-issue-93378.rs b/src/test/ui/fmt/format-args-capture-issue-93378.rs
new file mode 100644
index 00000000000..67444444264
--- /dev/null
+++ b/src/test/ui/fmt/format-args-capture-issue-93378.rs
@@ -0,0 +1,11 @@
+fn main() {
+    let a = "a";
+    let b = "b";
+
+    println!("{a} {b} {} {} {c} {}", c = "c");
+    //~^ ERROR: invalid reference to positional arguments 1 and 2 (there is 1 argument)
+
+    let n = 1;
+    println!("{a:.n$} {b:.*}");
+    //~^ ERROR: invalid reference to positional argument 0 (no arguments were given)
+}
diff --git a/src/test/ui/fmt/format-args-capture-issue-93378.stderr b/src/test/ui/fmt/format-args-capture-issue-93378.stderr
new file mode 100644
index 00000000000..588541044fe
--- /dev/null
+++ b/src/test/ui/fmt/format-args-capture-issue-93378.stderr
@@ -0,0 +1,22 @@
+error: invalid reference to positional arguments 1 and 2 (there is 1 argument)
+  --> $DIR/format-args-capture-issue-93378.rs:5:26
+   |
+LL |     println!("{a} {b} {} {} {c} {}", c = "c");
+   |                          ^^     ^^
+   |
+   = note: positional arguments are zero-based
+
+error: invalid reference to positional argument 0 (no arguments were given)
+  --> $DIR/format-args-capture-issue-93378.rs:9:23
+   |
+LL |     println!("{a:.n$} {b:.*}");
+   |               ------- ^^^--^
+   |               |          |
+   |               |          this precision flag adds an extra required argument at position 0, which is why there are 3 arguments expected
+   |               this parameter corresponds to the precision flag
+   |
+   = note: positional arguments are zero-based
+   = note: for information about formatting flags, visit https://doc.rust-lang.org/std/fmt/index.html
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/fmt/format-args-capture.rs b/src/test/ui/fmt/format-args-capture.rs
index e830a5bc9c5..d31d2a6c336 100644
--- a/src/test/ui/fmt/format-args-capture.rs
+++ b/src/test/ui/fmt/format-args-capture.rs
@@ -5,6 +5,7 @@ fn main() {
     named_argument_takes_precedence_to_captured();
     formatting_parameters_can_be_captured();
     capture_raw_strings_and_idents();
+    repeated_capture();
 
     #[cfg(panic = "unwind")]
     {
@@ -80,3 +81,10 @@ fn formatting_parameters_can_be_captured() {
     let s = format!("{x:-^width$.precision$}");
     assert_eq!(&s, "--7.000--");
 }
+
+fn repeated_capture() {
+    let a = 1;
+    let b = 2;
+    let s = format!("{a} {b} {a}");
+    assert_eq!(&s, "1 2 1");
+}