Add support for the Lean 4 LSP, served by lake. (#4952)

ale_linters/lean/lake.vim

@@ -0,0 +1,28 @@
+" Author: Benjamin Block <https://github.com/benjamindblock>
+" Description: A language server for Lean 4.
+
+function! ale_linters#lean#lake#GetProjectRoot(buffer) abort
+    let l:lakefile_toml = ale#path#FindNearestFile(a:buffer, 'lakefile.toml')
+    let l:lakefile_lean = ale#path#FindNearestFile(a:buffer, 'lakefile.lean')
+
+    if !empty(l:lakefile_toml)
+        return fnamemodify(l:lakefile_toml, ':p:h')
+    elseif !empty(l:lakefile_lean)
+        return fnamemodify(l:lakefile_lean, ':p:h')
+    else
+        return fnamemodify('', ':h')
+    endif
+endfunction
+
+call ale#Set('lean_lake_executable', 'lake')
+call ale#Set('lean_lake_config', {})
+
+call ale#linter#Define('lean', {
+\   'name': 'lake',
+\   'lsp': 'stdio',
+\   'language': 'lean',
+\   'lsp_config': {b -> ale#Var(b, 'lean_lake_config')},
+\   'executable': {b -> ale#Var(b, 'lean_lake_executable')},
+\   'command': '%e serve',
+\   'project_root': function('ale_linters#lean#lake#GetProjectRoot'),
+\})