Add a way to get mismatch backtrace using cfg

dtolnay · Jan 3, 2024 · cb94081 · cb94081
1 parent 3eb1857
commit cb94081
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Showing 2 changed files with 10 additions and 2 deletions.
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -76,7 +76,7 @@ jobs:
       - name: RUSTFLAGS='-Z allow-features=' cargo test
         run: cargo test
         env:
-          RUSTFLAGS: -Z allow-features= ${{env.RUSTFLAGS}}
+          RUSTFLAGS: -Z allow-features= --cfg procmacro2_backtrace ${{env.RUSTFLAGS}}
 
   minimal:
     name: Minimal versions

diff --git a/src/wrapper.rs b/src/wrapper.rs
@@ -40,7 +40,15 @@ impl LexError {
 
 #[cold]
 fn mismatch(line: u32) -> ! {
-    panic!("compiler/fallback mismatch #{}", line)
+    #[cfg(procmacro2_backtrace)]
+    {
+        let backtrace = std::backtrace::Backtrace::force_capture();
+        panic!("compiler/fallback mismatch #{}\n\n{}", line, backtrace)
+    }
+    #[cfg(not(procmacro2_backtrace))]
+    {
+        panic!("compiler/fallback mismatch #{}", line)
+    }
 }
 
 impl DeferredTokenStream {