From 5a75bbff7852752ffb09afc57b171dfcf4dbd51a Mon Sep 17 00:00:00 2001
From: "Paul A. Patience" <paul@apatience.com>
Date: Sat, 10 Jul 2021 12:12:46 -0400
Subject: doc-lookup: ignore BROWSER when empty.

* stdlib/doc-lookup.tl (open-url): Treat empty BROWSER variable
as if it were unset (i.e., ignore it). Otherwise the doc
function silently fails rather than falling back to alternative
URL-opening methods.

* txr.1: Documented.
---
 stdlib/doc-lookup.tl | 16 ++++++++--------
 txr.1                |  7 ++++---
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/stdlib/doc-lookup.tl b/stdlib/doc-lookup.tl
index e939aa2a..231d3b62 100644
--- a/stdlib/doc-lookup.tl
+++ b/stdlib/doc-lookup.tl
@@ -36,14 +36,14 @@
            (fallback '#"firefox iceweasel seamonkey mozilla \
                         epiphany konqueror chromium chromium-browser \
                         google-chrome"))
-       (let ((prog (or (getenv "BROWSER")
-                       (if (abs-path-p opener)
-                         opener
-                         (path-search opener))
-                       [find-true path-search fallback])))
-         (if prog
-           (detached-run prog (list url))
-           (error "~s: no URL-opening method available" 'open-url))))))
+       (iflet ((prog (getenv "BROWSER"))
+               (prog (or (and (plusp (len prog)) prog)
+                         (if (abs-path-p opener)
+                           opener
+                           (path-search opener))
+                         [find-true path-search fallback])))
+         (detached-run prog (list url))
+         (error "~s: no URL-opening method available" 'open-url)))))
   ((:cygwin :cygnal)
    (with-dyn-lib "shell32.dll"
      (deffi shell-execute "ShellExecuteW"
diff --git a/txr.1 b/txr.1
index c035ba39..82f53081 100644
--- a/txr.1
+++ b/txr.1
@@ -82571,9 +82571,10 @@ function is relied upon to open the URL.
 
 On other platforms, if the
 .code BROWSER
-environment variable exists, its value is assumed to indicate the
-name or path of the web-browsing program which can accept the URL
-as an argument. If this variable doesn't exist, then
+environment variable exists and is nonempty,
+its value is assumed to indicate the name or path
+of the web-browsing program which can accept the URL as an argument.
+If this variable doesn't exist or is empty, then
 .code doc
 searches for a system-dependent URL-opening utility, such as
 .codn xdg-open .
-- 
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