Close #4442 - Use Neovim diagnostics by default

Use Neovim's diagnostics API by default in recent enough Neovim
versions. This will make problems found by ALE play nicely with problems
found by other tools.

doc/ale.txt

@@ -121,7 +121,7 @@ circumstances.
 ALE will report problems with your code in the following ways, listed with
 their relevant options.
 
-* Via the Neovim diagnostics API (Off by default)  - |g:ale_use_neovim_diagnostics_api|
+* Via Neovim diagnostics (On in Neovim 0.6+)       - |g:ale_use_neovim_diagnostics_api|
 * By updating loclist. (On by default)             - |g:ale_set_loclist|
 * By updating quickfix. (Off by default)           - |g:ale_set_quickfix|
 * By setting error highlights.                     - |g:ale_set_highlights|
@@ -816,7 +816,6 @@ g:ale_command_wrapper                                   *g:ale_command_wrapper*
     " Has the same effect as the above.
     let g:ale_command_wrapper = 'nice -n5 %*'
 <
-
   For passing all of the arguments for a command as one argument to a wrapper,
   `%@` can be used instead. >
 
@@ -841,7 +840,6 @@ g:ale_completion_delay                                 *g:ale_completion_delay*
 
 g:ale_completion_enabled                             *g:ale_completion_enabled*
                                                      *b:ale_completion_enabled*
-
   Type: |Number|
   Default: `0`
 
@@ -907,7 +905,7 @@ g:ale_completion_excluded_words               *g:ale_completion_excluded_words*
 g:ale_completion_symbols                             *g:ale_completion_symbols*
 
   Type: |Dictionary|
-
+  Default: See `autoload/ale/completion.vim`
 
   A mapping from completion types to symbols for completions. See
   |ale-symbols| for more information.
@@ -986,7 +984,6 @@ g:ale_cursor_detail                                       *g:ale_cursor_detail*
 
 g:ale_default_navigation                             *g:ale_default_navigation*
                                                      *b:ale_default_navigation*
-
   Type: |String|
   Default: `'buffer'`
 
@@ -1005,7 +1002,6 @@ g:ale_detail_to_floating_preview             *g:ale_detail_to_floating_preview*
 
 g:ale_disable_lsp                                           *g:ale_disable_lsp*
                                                             *b:ale_disable_lsp*
-
   Type: |Number|
   Default: `0`
 
@@ -1056,7 +1052,6 @@ g:ale_echo_msg_error_str                             *g:ale_echo_msg_error_str*
 
 g:ale_echo_msg_format                                   *g:ale_echo_msg_format*
                                                         *b:ale_echo_msg_format*
-
   Type: |String|
   Default: `'%code: %%s'`
 
@@ -1129,7 +1124,6 @@ g:ale_enabled                                                   *g:ale_enabled*
   " Disable linting for all minified JS files.
   let g:ale_pattern_options = {'\.min.js$': {'ale_enabled': 0}}
 <
-
   See |g:ale_pattern_options| for more information on that option.
 
 
@@ -1138,6 +1132,8 @@ g:ale_exclude_highlights                             *g:ale_exclude_highlights*
   Type: |List|
   Default: `[]`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   A list of regular expressions for matching against highlight messages to
   remove. For example: >
 
@@ -1828,6 +1824,8 @@ g:ale_max_signs                                               *g:ale_max_signs*
   Type: |Number|
   Default: `-1`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   When set to any positive integer, ALE will not render any more than the
   given number of signs for any one buffer.
 
@@ -2036,6 +2034,11 @@ g:ale_set_highlights                                     *g:ale_set_highlights*
   Type: |Number|
   Default: `has('syntax')`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+  In addition, ALE's highlight groups will not be used when setting
+  highlights through Neovim's diagnostics API. See |diagnostic-highlights| for
+  how to configure Neovim diagnostic highlighting.
+
   When this option is set to `1`, highlights will be set for problems.
 
   ALE will use the following highlight groups for problems:
@@ -2097,8 +2100,10 @@ g:ale_set_signs                                               *g:ale_set_signs*
   signs marking where problems appear in the file.
 
   When |g:ale_use_neovim_diagnostics_api| is `1`, the only other setting that
-  will be respected for signs is |g:ale_sign_priority|. No other settings,
+  will be respected for signs is |g:ale_sign_priority|. ALE's highlight groups
-  highlights, text, or behaviors will apply.
+  will and other sign settings will not apply when setting signs through
+  Neovim's diagnostics API. See |diagnostic-signs| for how to configure signs
+  in Neovim.
 
   ALE will use the following highlight groups for problems:
 
@@ -2183,6 +2188,8 @@ g:ale_sign_column_always                             *g:ale_sign_column_always*
   Type: |Number|
   Default: `0`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   By default, the sign gutter will disappear when all warnings and errors have
   been fixed for a file. When this option is set to `1`, the sign column will
   remain open. This can be preferable if you don't want the text in your file
@@ -2194,6 +2201,8 @@ g:ale_sign_error                                             *g:ale_sign_error*
   Type: |String|
   Default: `'>>'`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   The sign for errors in the sign gutter.
 
 
@@ -2202,6 +2211,8 @@ g:ale_sign_info                                               *g:ale_sign_info*
   Type: |String|
   Default: `g:ale_sign_warning`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   The sign for "info" markers in the sign gutter.
 
 
@@ -2210,6 +2221,8 @@ g:ale_sign_style_error                                 *g:ale_sign_style_error*
   Type: |String|
   Default: `g:ale_sign_error`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   The sign for style errors in the sign gutter.
 
 
@@ -2218,6 +2231,8 @@ g:ale_sign_style_warning                             *g:ale_sign_style_warning*
   Type: |String|
   Default: `g:ale_sign_warning`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   The sign for style warnings in the sign gutter.
 
 
@@ -2226,6 +2241,8 @@ g:ale_sign_offset                                           *g:ale_sign_offset*
   Type: |Number|
   Default: `1000000`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   This variable controls offset from which numeric IDs will be generated for
   new signs. Signs cannot share the same ID values, so when two Vim plugins
   set signs at the same time, the IDs have to be configured such that they do
@@ -2240,6 +2257,8 @@ g:ale_sign_warning                                         *g:ale_sign_warning*
   Type: |String|
   Default: `'--'`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   The sign for warnings in the sign gutter.
 
 
@@ -2248,6 +2267,8 @@ g:ale_sign_highlight_linenrs                     *g:ale_sign_highlight_linenrs*
   Type: |Number|
   Default: `0`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   When set to `1`, this option enables highlighting problems on the 'number'
   column in Vim versions that support `numhl` highlights. This option must be
   configured before ALE is loaded.
@@ -2305,16 +2326,13 @@ g:ale_use_global_executables                     *g:ale_use_global_executables*
 g:ale_use_neovim_diagnostics_api             *g:ale_use_neovim_diagnostics_api*
 
   Type: |Number|
-  Default: `0`
+  Default: `has('nvim-0.6')`
 
   If enabled, this option will disable ALE's standard UI, and instead send
   all linter output to Neovim's diagnostics API. This allows you to collect
   errors from nvim-lsp, ALE, and anything else that uses diagnostics all in
-  one place. The following options are ignored when using the diagnostics API:
+  one place. Many options for configuring how problems appear on the screen
-
+  will not apply when the API is enabled.
-    - |g:ale_set_highlights|
-    - |g:ale_set_signs|
-    - |g:ale_virtualtext_cursor|
 
   To enable this option, set the value to `1`.
 
@@ -2334,11 +2352,17 @@ g:ale_virtualtext_cursor                             *g:ale_virtualtext_cursor*
   `'current'`, `'1'`, or `1`     - Show problems for the current line.
   `'disabled'`, `'0'`, or `0`    - Do not show problems with virtual-text.
 
+  When |g:ale_use_neovim_diagnostics_api| is `1`, `'current'` will behave the
+  same as `'all'`.
+
   Messages are only displayed after a short delay. See |g:ale_virtualtext_delay|.
 
-  Messages can be prefixed with a string. See |g:ale_virtualtext_prefix|.
+  Messages can be prefixed with a string if not using Neovim's diagnostics
+  API. See |g:ale_virtualtext_prefix|.
 
-  ALE will use the following highlight groups for problems:
+  If and only if not displaying problems via Neovim's diagnostics API,
+  highlights for configuring ALE's virtualtext messages can be configured with
+  custom highlight groups:
 
   |ALEVirtualTextError|        - Items with `'type': 'E'`
   |ALEVirtualTextWarning|      - Items with `'type': 'W'`
@@ -2352,6 +2376,8 @@ g:ale_virtualtext_delay                               *g:ale_virtualtext_delay*
   Type: |Number|
   Default: `10`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   Given any integer, this option controls the number of milliseconds before
   ALE will show a message for a problem near the cursor.
 
@@ -2364,6 +2390,8 @@ g:ale_virtualtext_prefix                             *g:ale_virtualtext_prefix*
   Type: |String|
   Default: `'%comment% %type%: '`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   Prefix to be used with |g:ale_virtualtext_cursor|.
 
   This setting can be changed in each buffer with `b:ale_virtualtext_prefix`.
@@ -2385,6 +2413,8 @@ g:ale_virtualtext_maxcolumn                       *g:ale_virtualtext_maxcolumn*
   Type: |String| or |Number|
   Default: `0`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   Virtualtext column range, from `column` to `maxcolumn`.  If a line is
   `column` or less characters long, the virtualtext message is shifted right
   to `column`.
@@ -2406,6 +2436,8 @@ g:ale_virtualtext_single                             *g:ale_virtualtext_single*
   Type: |Number|
   Default: `0`
 
+  This setting has no effect when |g:ale_use_neovim_diagnostics_api| is `1`.
+
   Enable or disable concatenation of multiple virtualtext messages on a single
   line.  By default, if a line has multiple errors or warnings, each will be
   appended in turn.

plugin/ale.vim

@@ -197,7 +197,7 @@ let g:ale_save_hidden = get(g:, 'ale_save_hidden', 0)
 
 " If 1, disables ALE's built in error display. Instead, all errors are piped
 " to the diagnostics API.
-let g:ale_use_neovim_diagnostics_api = get(g:, 'ale_use_neovim_diagnostics_api', 0)
+let g:ale_use_neovim_diagnostics_api = get(g:, 'ale_use_neovim_diagnostics_api', has('nvim-0.6'))
 
 if g:ale_use_neovim_diagnostics_api && !has('nvim-0.6')
     " no-custom-checks

test/vimrc

@@ -2,6 +2,8 @@
 
 " Make most tests just set lists synchronously when run in Docker, etc.
 let g:ale_set_lists_synchronously = 1
+" Disable Neovim diagnostics by default for CI tests.
+let g:ale_use_neovim_diagnostics_api = 0
 
 " This lowercase highlight definition is needed for highlight tests.
 hi link aleerrorline spellbad