Tweak minor details of #58153 fix.

* ChangeLog: Explain root-clause analysis more completely.
* src/roff/troff/input.cpp: Use same brief-scope variable names as
  earlier code for better continuity.

2 files changed, 10 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 07d5fbe8b..e4954897d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -60,7 +60,12 @@
 	get_location() for its side effect of rewriting a filename of
 	"-" to "<standard input>", for consistency with other diagnostic
 	messages.  (In this class, this member function always returns
-	1, so ignore the return value.)
+	1, so ignore the return value.  This fact is an essential part
+	of what led to the bug; the conditional
+		p && !p->get_location(0, &f, &n)
+	which appeared in the for loop of the old
+	input_stack::backtrace() would always evaluate to false when a
+	node of the file_iterator class was encountered.)
 	(input_stack::backtrace): Replace member function body with that
 	of input_stack::backtrace_all().
 	(input_stack::backtrace_all): Delete.
diff --git a/src/roff/troff/input.cpp b/src/roff/troff/input.cpp
index f35fcbf3c..26394ade0 100644
--- a/src/roff/troff/input.cpp
+++ b/src/roff/troff/input.cpp
@@ -401,13 +401,13 @@ int file_iterator::get_location(int /*allow_macro*/,
 
 void file_iterator::backtrace()
 {
-  const char *fn;
-  int l;
+  const char *f;
+  int n;
   // Get side effect of filename rewrite if stdin.
-  (void) get_location(0, &fn, &l);
+  (void) get_location(0, &f, &n);
   if (program_name)
     fprintf(stderr, "%s: ", program_name);
-  errprint("backtrace: %3 '%1':%2\n", fn, l, popened ? "pipe" : "file");
+  errprint("backtrace: %3 '%1':%2\n", f, n, popened ? "pipe" : "file");
 }
 
 int file_iterator::set_location(const char *f, int ln)