fix: don't steal focus when an async weather response renders

wttrin--display-weather ran switch-to-buffer from the async callback, so a
response arriving after the user moved to another buffer yanked them back to
*wttr.in*. It now renders with set-buffer; selecting the buffer is the
interactive command's job (wttrin-query already does it at invocation), so a
late response updates the buffer in place without changing the selected window.

3 files changed, 54 insertions, 5 deletions

diff --git a/tests/test-wttrin--display-weather-focus.el b/tests/test-wttrin--display-weather-focus.el
new file mode 100644
index 0000000..cc08fdd
--- /dev/null
+++ b/tests/test-wttrin--display-weather-focus.el
@@ -0,0 +1,45 @@
+;;; test-wttrin--display-weather-focus.el --- Async render doesn't steal focus -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2024-2026 Craig Jennings
+
+;;; Commentary:
+;; wttrin--display-weather runs from an async callback.  If the user moved to
+;; another buffer while the fetch was in flight, rendering the result must not
+;; select *wttr.in* and steal the window.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin)
+(require 'testutil-wttrin)
+
+(ert-deftest test-wttrin--display-weather-error-does-not-steal-focus ()
+  "Error: rendering an async response does not select *wttr.in*.
+If the user moved to another buffer while the fetch was in flight, displaying
+the result must leave the selected window on that other buffer."
+  (let ((other (get-buffer-create "*wttrin-other*")))
+    (unwind-protect
+        (progn
+          (set-window-buffer (selected-window) other)
+          (wttrin--display-weather "Paris" "Weather report: paris\n+10 C\n"
+                                   nil nil nil)
+          (should (eq (window-buffer (selected-window)) other)))
+      (when (get-buffer "*wttr.in*") (kill-buffer "*wttr.in*"))
+      (when (buffer-live-p other) (kill-buffer other)))))
+
+(ert-deftest test-wttrin--display-weather-normal-populates-buffer ()
+  "Normal: rendering still fills *wttr.in* with the weather content."
+  (let ((other (get-buffer-create "*wttrin-other*")))
+    (unwind-protect
+        (progn
+          (set-window-buffer (selected-window) other)
+          (wttrin--display-weather "Paris" "Weather report: paris\n+10 C\n"
+                                   nil nil nil)
+          (with-current-buffer "*wttr.in*"
+            (should (string-match-p "Weather report: Paris"
+                                    (buffer-string)))))
+      (when (get-buffer "*wttr.in*") (kill-buffer "*wttr.in*"))
+      (when (buffer-live-p other) (kill-buffer other)))))
+
+(provide 'test-wttrin--display-weather-focus)
+;;; test-wttrin--display-weather-focus.el ends here
diff --git a/tests/test-wttrin--display-weather.el b/tests/test-wttrin--display-weather.el
index 99ea067..3b9cdee 100644
--- a/tests/test-wttrin--display-weather.el
+++ b/tests/test-wttrin--display-weather.el
@@ -51,7 +51,10 @@ Weather report: Paris, France
 ;;; Normal Cases
 
 (ert-deftest test-wttrin--display-weather-normal-valid-data-creates-buffer ()
-  "Test that valid weather data creates and displays buffer correctly."
+  "Test that valid weather data creates and fills the buffer correctly.
+Display is the interactive command's job (wttrin-query selects the buffer at
+invocation); this async render only updates content, so it does not select a
+window."
   (test-wttrin--display-weather-setup)
   (unwind-protect
       (testutil-wttrin-with-clean-weather-buffer
@@ -60,9 +63,6 @@ Weather report: Paris, France
         ;; Buffer should exist
         (should (get-buffer "*wttr.in*"))
 
-        ;; Buffer should be displayed
-        (should (get-buffer-window "*wttr.in*"))
-
         ;; Buffer should have content
         (with-current-buffer "*wttr.in*"
           (should (> (buffer-size) 0))
diff --git a/wttrin.el b/wttrin.el
index e34fdb5..c0359d9 100644
--- a/wttrin.el
+++ b/wttrin.el
@@ -1176,7 +1176,11 @@ coordinates but can name the place)."
                      "Cannot retrieve weather data. Perhaps the location was misspelled?"))
       (wttrin--add-to-location-history display)
       (let ((buffer (get-buffer-create (format "*wttr.in*"))))
-        (switch-to-buffer buffer)
+        ;; Render into the buffer without selecting it.  This runs from an
+        ;; async callback; the command (wttrin-query) already showed the buffer
+        ;; at invocation time, so re-selecting here would steal focus if the
+        ;; user moved away while the fetch was in flight.
+        (set-buffer buffer)
 
         ;; wttrin-mode calls kill-all-local-variables, so it must run
         ;; before setting any buffer-local state (xterm-color, location)