Allow requesting try_lint() to only run linters supporting stdin

When hooking linting to an event like InsertLeave, running linters that
only work with content that already made to the storage does not make
sense.

Enhance try_lint() to accept an optional boolean flag stdin_only in its
set of options. When this flag is present and set to "true" try_lint()
will skip all linters that do not advertise stdin support (via
linter.stdin).

Author: dtor

doc/lint.txt

@@ -32,8 +32,8 @@ M.try_lint({names?}, {opts?})                                    *lint.try_lint*
 
 
     Parameters: ~
-        {names?}  (string|string[])                       name of the linter
-        {opts?}   ({cwd?:string,ignore_errors?:boolean})  options
+        {names?}  (string|string[])                                           name of the linter
+        {opts?}   ({cwd?:string,ignore_errors?:boolean,stdin_only?:boolean})  options
 
 
 M.get_namespace({name})                                     *lint.get_namespace*

lua/lint.lua

@@ -54,7 +54,7 @@ M.linters_by_ft = {
 --- If no names are given, it runs the linters configured in `linters_by_ft`
 ---
 ---@param names? string|string[] name of the linter
----@param opts? {cwd?: string, ignore_errors?: boolean} options
+---@param opts? {cwd?: string, ignore_errors?: boolean, stdin_only?: boolean} options
 function M.try_lint(names, opts)
   assert(
     vim.diagnostic,
@@ -82,16 +82,21 @@ function M.try_lint(names, opts)
   local running_procs = running_procs_by_buf[bufnr] or {}
   for _, linter_name in pairs(names) do
     local linter = lookup_linter(linter_name)
-    local proc = running_procs[linter.name]
-    if proc then
-      proc:cancel()
-    end
-    running_procs[linter.name] = nil
-    local ok, lintproc_or_error = pcall(M.lint, linter, opts)
-    if ok then
-      running_procs[linter.name] = lintproc_or_error
-    elseif not opts.ignore_errors then
-      notify(lintproc_or_error --[[@as string]], vim.log.levels.WARN)
+    if not opts.stdin_only or linter.stdin then
+      local proc = running_procs[linter.name]
+      if proc then
+        proc:cancel()
+      end
+      running_procs[linter.name] = nil
+      local ok, lintproc_or_error = pcall(M.lint, linter, {
+        cwd = opts.cwd,
+        ignore_errors = opts.ignore_errors,
+      })
+      if ok then
+        running_procs[linter.name] = lintproc_or_error
+      elseif not opts.ignore_errors then
+        notify(lintproc_or_error --[[@as string]], vim.log.levels.WARN)
+      end
     end
   end
   running_procs_by_buf[bufnr] = running_procs