'main': Fix issue zsh-users#677, concerning multiline aliases.

The fix is to exempt such aliases from the empty commands sanity check.

Author: danielshahaf

highlighters/main/main-highlighter.zsh

@@ -750,9 +750,17 @@ _zsh_highlight_main_highlighter_highlight_list()
        style=commandseparator
      elif [[ $this_word == *':start:'* ]] && [[ $arg == $'\n' ]]; then
        style=commandseparator
+     elif [[ $this_word == *':start:'* ]] && [[ $arg == ';' ]] && (( in_alias )); then
+       style=commandseparator
      else
-       # This highlights empty commands (semicolon follows nothing) as an error.
-       # Zsh accepts them, though.
+       # Empty commands (semicolon follows nothing) are valid syntax.
+       # However, in interactive use they are likely to be erroneous;
+       # therefore, we highlight them as errors.
+       #
+       # Alias definitions are exempted from this check to allow multiline aliases
+       # with explicit (redundant) semicolons: «alias foo=$'bar;\nbaz'» (issue #677).
+       #
+       # See also #691 about possibly changing the style used here.
        style=unknown-token
      fi
 

highlighters/main/test-data/alias-comment1.zsh

@@ -33,5 +33,5 @@ alias x=$'# foo\npwd'
 BUFFER='x'
 
 expected_region_highlight=(
-  '1 1 alias "issue #677"' # x
+  '1 1 alias' # x
 )