Rollup merge of #114511 - chenyukang:yukang-fix-114374-fmt-args, r=b-naber

Remove the unhelpful let binding diag comes from FormatArguments

Fixes #114374

2 files changed, 49 insertions, 0 deletions

diff --git a/tests/ui/borrowck/issue-114374-invalid-help-fmt-args.rs b/tests/ui/borrowck/issue-114374-invalid-help-fmt-args.rs
new file mode 100644
index 00000000000..4a6c2f9ed06
--- /dev/null
+++ b/tests/ui/borrowck/issue-114374-invalid-help-fmt-args.rs
@@ -0,0 +1,16 @@
+#![allow(dead_code)]
+
+fn bar<'a>(_: std::fmt::Arguments<'a>) {}
+fn main() {
+    let x = format_args!("a {} {} {}.", 1, format_args!("b{}!", 2), 3);
+    //~^ ERROR temporary value dropped while borrowed
+
+    bar(x);
+
+    let foo = format_args!("{}", "hi");
+    //~^ ERROR temporary value dropped while borrowed
+    bar(foo);
+
+    let foo = format_args!("hi"); // no placeholder in arguments, so no error
+    bar(foo);
+}
diff --git a/tests/ui/borrowck/issue-114374-invalid-help-fmt-args.stderr b/tests/ui/borrowck/issue-114374-invalid-help-fmt-args.stderr
new file mode 100644
index 00000000000..8221505b100
--- /dev/null
+++ b/tests/ui/borrowck/issue-114374-invalid-help-fmt-args.stderr
@@ -0,0 +1,33 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/issue-114374-invalid-help-fmt-args.rs:5:13
+   |
+LL |     let x = format_args!("a {} {} {}.", 1, format_args!("b{}!", 2), 3);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^- temporary value is freed at the end of this statement
+   |             |
+   |             creates a temporary value which is freed while still in use
+...
+LL |     bar(x);
+   |         - borrow later used here
+   |
+   = note: the result of `format_args!` can only be assigned directly if no placeholders in it's arguments are used
+   = note: to learn more, visit <https://doc.rust-lang.org/std/macro.format_args.html>
+   = note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/issue-114374-invalid-help-fmt-args.rs:10:15
+   |
+LL |     let foo = format_args!("{}", "hi");
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^- temporary value is freed at the end of this statement
+   |               |
+   |               creates a temporary value which is freed while still in use
+LL |
+LL |     bar(foo);
+   |         --- borrow later used here
+   |
+   = note: the result of `format_args!` can only be assigned directly if no placeholders in it's arguments are used
+   = note: to learn more, visit <https://doc.rust-lang.org/std/macro.format_args.html>
+   = note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0716`.