Avoid oscillating line wrapping due to symbol indices

tests/ui/hygiene/unpretty-debug-lifetimes.rs

@@ -4,8 +4,15 @@
 // Regression test for lifetime hygiene annotations in -Zunpretty=expanded,hygiene
 // Previously, lifetimes were missing the #N syntax context suffix.
 
-// Don't break whenever Symbol numbering changes
-//@ normalize-stdout: "\d+#" -> "0#"
+// This test deliberately has no `.stdout` snapshot. The hygiene annotations
+// embed `Symbol` indices, whose width feeds into the pretty-printer's line
+// breaking, so the layout shifts whenever a `Symbol` gains or loses a digit.
+// `normalize-stdout` can't help, because the layout is decided before
+// normalization runs. Assert the property this test is about instead: the two
+// `'a` share their text but carry different syntax contexts.
+//@ dont-check-compiler-stdout
+//@ check-stdout
+//@ regex-error-pattern: f\s*/\*\s*\d+#0\s*\*/<'a\s*/\*\s*\d+#0\s*\*/,\s*'a\s*/\*\s*\d+#1\s*\*/
 
 #![feature(decl_macro)]
 #![feature(no_core)]