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, 10 insertions, 0 deletions

diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 3cdd3a4b2c3..b293aa8de38 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -52,6 +52,16 @@ pub fn expand_column(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
     base::MacEager::expr(cx.expr_u32(topmost, loc.col.to_usize() as u32))
 }
 
+/* __rust_unstable_column!(): expands to the current column number */
+pub fn expand_column_gated(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
+                  -> Box<base::MacResult+'static> {
+    if sp.allows_unstable() {
+        expand_column(cx, sp, tts)
+    } else {
+        cx.span_fatal(sp, "the __rust_unstable_column macro is unstable");
+    }
+}
+
 /// file!(): expands to the current filename */
 /// The filemap (`loc.file`) contains a bunch more information we could spit
 /// out if we wanted.