'main': Don't highlight unknown precommand flags as errors.

We cannot now for sure whether the flag is misspelled or simply unknown to us,
so err on the side of caution.  This fixes an unreleased regression.  Fixes #658.

Issue #641 was originally filed about this problem, but is left open to track
further enhancements.

highlighters/main/main-highlighter.zsh

@@ -662,12 +662,9 @@ _zsh_highlight_main_highlighter_highlight_list()
           next_word+=':start:'
           next_word+=':sudo_opt:'
         elif [[ $arg == '-'* ]]; then
-          # Unknown flag
+          # Unknown flag.  We don't know whether it takes an argument or not,
+          # so we don't modify $next_word.
           this_word=':sudo_opt:'
-          next_word+=':start:'
-          next_word+=':sudo_opt:'
-          _zsh_highlight_main_add_region_highlight $start_pos $end_pos unknown-token
-          continue
         else
           # Not an option flag; nothing to do.  (If the command line is
           # syntactically valid, ${this_word//:sudo_opt:/} should be

highlighters/main/test-data/precommand-unknown-option.zsh

@@ -38,6 +38,6 @@ expected_region_highlight=(
   '10 11 command' # ls
   '12 12 commandseparator' # ;
   '14 17 precommand' # sudo
-  '19 20 unknown-token' # -x
-  '22 23 command' # ls
+  '19 20 single-hyphen-option' # -x
+  '22 23 default' # ls
 )

highlighters/main/test-data/sudo-longopt.zsh

@@ -32,6 +32,6 @@ BUFFER='sudo --askpass ls'
 
 expected_region_highlight=(
   '1 4 precommand' # sudo
-  '6 14 double-hyphen-option "issues #641 and #658"' # --askpass
-  '16 17 default "issues #641 and #658"' # ls (we don't know whether --askpass takes an argument)
+  '6 14 double-hyphen-option' # --askpass
+  '16 17 default' # ls (we don't know whether --askpass takes an argument)
 )