fix #45171, keyword sorter location should just be definition line

src/julia-syntax.scm

@@ -543,7 +543,7 @@
         ,(method-def-expr-
           name positional-sparams pargl-all
           `(block
-            ,@(without-generated prologue)
+            ,@(keep-first linenum? (without-generated prologue))
             ,(let (;; call mangled(vals..., [rest_kw,] pargs..., [vararg]...)
                    (ret `(return (call ,mangled
                                        ,@(if ordered-defaults keynames vals)
@@ -562,7 +562,7 @@
              ,(if (any kwarg? pargl) (gensy) UNUSED)
              (call (core kwftype) ,ftype)) ,kw ,@pargl ,@vararg)
           `(block
-            ,@(filter linenum? prologue)
+            ,@(keep-first linenum? prologue)
             ;; nospecialize meta for just positional args
             ,@(map (lambda (m)
                      `(meta ,(cadr m) ,@(filter (lambda (v) (not (memq v keynames)))

src/utils.scm

@@ -104,3 +104,11 @@
           (begin (put! tbl (car xs) i)
                  (loop (cdr xs) (+ i 1)))))
     tbl))
+
+;; keep at most the first element matching a given predicate
+(define (keep-first pred lst)
+  (cond ((null? lst) lst)
+        ((pred (car lst))
+         (cons (car lst) (filter (lambda (x) (not (pred x))) (cdr lst))))
+        (else
+         (cons (car lst) (keep-first pred (cdr lst))))))

test/backtrace.jl

@@ -224,6 +224,19 @@ let trace = try
     @test trace[1].line == 2
 end
 
+# issue #45171
+linenum = @__LINE__; function f45171(;kwarg = true)
+    1
+    error()
+end
+let trace = try
+        f45171()
+    catch
+        stacktrace(catch_backtrace())
+    end
+    @test trace[3].line == linenum
+end
+
 # issue #29695 (see also test for #28442)
 let code = """
     f29695(c) = g29695(c)