external: do not crash if command can't be found

bebop/browser/browser.py

@@ -675,7 +675,10 @@ class Browser:
             return
 
         command = self.config["source_editor"] + [source_filename]
-        open_external_program(command)
+        success = open_external_program(command)
+        if not success:
+            self.set_status_error("Could not open editor.")
+
         if delete_source_after:
             os.unlink(source_filename)
         self.refresh_windows()

bebop/command_line.py

@@ -200,7 +200,9 @@ class CommandLine:
             return
 
         command = self.editor_command + [temp_filepath]
-        open_external_program(command)
+        success = open_external_program(command)
+        if not success:
+            return
 
         try:
             with open(temp_filepath, "rt") as temp_file:

bebop/external.py

@@ -1,6 +1,7 @@
 """Call external commands."""
 
 import curses
+import logging
 import subprocess
 
 
@@ -9,12 +10,21 @@ def open_external_program(command):
 
     The caller has to refresh whatever windows it manages after calling this
     method or garbage may be left on the screen.
+
+    Returns:
+    True if no exception occured.
     """
     curses.nocbreak()
     curses.echo()
     curses.curs_set(1)
+    result = True
+    try:
         subprocess.run(command)
+    except OSError as exc:
+        logging.error(f"Failed to run '{command}': {exc}")
+        result = False
     curses.mousemask(curses.ALL_MOUSE_EVENTS)
     curses.curs_set(0)
     curses.noecho()
     curses.cbreak()
+    return result