Add htmlhint (simple html linter) (#491)

README.md

@@ -125,6 +125,7 @@ Other dedicated linters that are built-in are:
 | [DirectX Shader Compiler][dxc]     | `dxc`                  |
 | [hadolint][28]                     | `hadolint`             |
 | [hlint][32]                        | `hlint`                |
+| [htmlhint][htmlhint]               | `htmlhint`             |
 | [HTML Tidy][12]                    | `tidy`                 |
 | [Inko][17]                         | `inko`                 |
 | [janet][janet]                     | `janet`                |
@@ -495,3 +496,4 @@ busted tests/
 [regal]: https://github.com/StyraInc/regal
 [vala-lint]: https://github.com/vala-lang/vala-lint
 [systemdlint]: https://github.com/priv-kweihmann/systemdlint
+[htmlhint]: https://htmlhint.com/

lua/lint/linters/htmlhint.lua

@@ -0,0 +1,24 @@
+local pattern = '.*: line (%d+), col (%d+), (%a+) %- (.+) %((.+)%)'
+local groups = { 'lnum', 'col', 'severity', 'message', 'code' }
+local severities = {
+  error = vim.diagnostic.severity.ERROR,
+  warning = vim.diagnostic.severity.WARN,
+}
+
+return {
+  cmd = "htmlhint",
+  stdin = true,
+  args = {
+    "stdin",
+    "-f",
+    "compact",
+  },
+  stream = "stdout",
+  ignore_exitcode = true,
+  parser = require('lint.parser').from_pattern(
+    pattern,
+    groups,
+    severities,
+    { source = "htmlhint" }
+  )
+}