Auto merge of #43735 - est31:master, r=alexcrichton

Avoid calling the column!() macro in panic

Closes #43057

This "fix" adds a new macro called `__rust_unstable_column` and to use it instead of the `column` macro inside panic. The new macro can be shadowed as well as `column` can, but its very likely that there is no code that does this in practice.

There is no real way to make "unstable" macros that are usable by stable macros, so we do the next best thing and prefix the macro with `__rust_unstable` to make sure people recognize it is unstable.

r? @alexcrichton

1 files changed, 14 insertions, 2 deletions

diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 03db1e4f01c..5e88a46ecc3 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -14,6 +14,16 @@
 //! library. Each macro is available for use when linking against the standard
 //! library.
 
+#[macro_export]
+// This stability attribute is totally useless.
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg(stage0)]
+macro_rules! __rust_unstable_column {
+    () => {
+        column!()
+    }
+}
+
 /// The entry point for panic of Rust threads.
 ///
 /// This macro is used to inject panic into a Rust thread, causing the thread to
@@ -48,7 +58,8 @@ macro_rules! panic {
     ($msg:expr) => ({
         $crate::rt::begin_panic($msg, {
             // static requires less code at runtime, more constant data
-            static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(), column!());
+            static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(),
+                __rust_unstable_column!());
             &_FILE_LINE_COL
         })
     });
@@ -58,7 +69,8 @@ macro_rules! panic {
             // used inside a dead function. Just `#[allow(dead_code)]` is
             // insufficient, since the user may have
             // `#[forbid(dead_code)]` and which cannot be overridden.
-            static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(), column!());
+            static _FILE_LINE_COL: (&'static str, u32, u32) = (file!(), line!(),
+                __rust_unstable_column!());
             &_FILE_LINE_COL
         })
     });