ui: Do not attempt to display the line preceding the 0th.

* ccwl/ui.scm (source-in-context): Do not attempt to display the line
preceding the 0th.
* tests/ui.scm ("display source in context on 0th line"): New line.

2 files changed, 18 insertions, 8 deletions

diff --git a/ccwl/ui.scm b/ccwl/ui.scm
index c499041..7f5c76a 100644
--- a/ccwl/ui.scm
+++ b/ccwl/ui.scm
@@ -124,14 +124,16 @@ with S-expression at LINE-NUMBER, COLUMN-NUMBER highlit in
 red. LINE-NUMBER and COLUMN-NUMBER are zero-based."
   (call-with-output-string
     (lambda (out)
-      ;; Get to line preceding syntax x.
-      (repeat (cut get-line port)
-              (max 0 (1- line-number)))
-      ;; Display line preceding syntax x unless blank.
-      (let ((line (get-line port)))
-        (unless (or (zero? line-number)
-                    (string-blank? line))
-          (put-line line out)))
+      ;; Unless the 0th line is requested, display line preceding
+      ;; syntax x.
+      (unless (zero? line-number)
+        ;; Get to line preceding syntax x.
+        (repeat (cut get-line port)
+                (1- line-number))
+        ;; Display line preceding syntax x unless blank.
+        (let ((line (get-line port)))
+          (unless (string-blank? line)
+            (put-line line out))))
       ;; Display part of line before syntax x.
       (display (get-string-n port column-number)
                out)
diff --git a/tests/ui.scm b/tests/ui.scm
index f7810d7..4189e6c 100644
--- a/tests/ui.scm
+++ b/tests/ui.scm
@@ -35,4 +35,12 @@
 "
     (cut source-in-context <> 1 2)))
 
+(test-equal "display source in context on 0th line"
+  (string-append "(foo "
+                 (colorize-string "(bar)" 'BOLD 'RED)
+                 ")
+")
+  (call-with-input-string "(foo (bar))"
+    (cut source-in-context <> 0 5)))
+
 (test-end "ui")