feat: get_available_servers now accepts a filter (#25)

Co-authored-by: William Boman <william@redwill.se>

doc/mason-lspconfig.txt

@@ -234,7 +234,7 @@ get_installed_servers()
         |mason-registry.get_installed_package_names()|
 
                                      *mason-lspconfig.get_available_servers()*
-get_available_servers()
+get_available_servers({filter})
     Returns the available (both installed & uninstalled) LSP servers.
 
     Note: ~
@@ -244,6 +244,12 @@ get_available_servers()
         table and use its values to directly interact with lspconfig (for
         example setting up all installed servers).
 
+    Parameters: ~
+        {filter}  (table|nil) A table with key-value pairs used to
+                  filter the list of server names. The available keys are:
+                  - filetype (string | string[]): Only return servers with
+                    matching filetype
+
     Returns: ~
         string[]
 

lua/mason-lspconfig/init.lua

@@ -78,16 +78,53 @@ function M.get_installed_servers()
     end, registry.get_installed_package_names())
 end
 
+---@param filetype string | string[]
+local function is_server_in_filetype(filetype)
+    local filetype_mapping = require "mason-lspconfig.mappings.filetype"
+
+    local function get_servers_by_filetype(ft)
+        return filetype_mapping[ft] or {}
+    end
+
+    local server_candidates = _.compose(
+        _.set_of,
+        _.cond {
+            { _.is "string", get_servers_by_filetype },
+            { _.is "table", _.compose(_.flatten, _.map(get_servers_by_filetype)) },
+            { _.T, _.always {} },
+        }
+    )(filetype)
+
+    ---@param server_name string
+    ---@return boolean
+    return function(server_name)
+        return server_candidates[server_name]
+    end
+end
+
 ---Get a list of available servers in mason-registry
+---@param filter { filetype: string | string[] }?: (optional) Used to filter the list of server names.
+--- The available keys are
+---   - filetype (string | string[]): Only return servers with matching filetype
 ---@return string[]
-function M.get_available_servers()
+function M.get_available_servers(filter)
     local registry = require "mason-registry"
     local server_mapping = require "mason-lspconfig.mappings.server"
     local Optional = require "mason-core.optional"
-    local server_names = _.filter_map(function(pkg_name)
-        return Optional.of_nilable(server_mapping.package_to_lspconfig[pkg_name])
+    filter = filter or {}
+    local predicates = {}
+
+    if filter.filetype then
+        table.insert(predicates, is_server_in_filetype(filter.filetype))
+    end
+
+    return _.filter_map(function(pkg_name)
+        return Optional.of_nilable(server_mapping.package_to_lspconfig[pkg_name]):map(function(server_name)
+            if #predicates == 0 or _.all_pass(predicates, server_name) then
+                return server_name
+            end
+        end)
     end, registry.get_all_package_names())
-    return server_names
 end
 
 return M

tests/mason-lspconfig/api/api_spec.lua

@@ -0,0 +1,43 @@
+local mason_lspconfig = require "mason-lspconfig"
+local _ = require "mason-core.functional"
+
+describe("mason-lspconfig API", function()
+    it("should return all available servers", function()
+        local server_mappings = require "mason-lspconfig.mappings.server"
+        local available_servers = mason_lspconfig.get_available_servers()
+        assert.equal(#vim.tbl_keys(server_mappings.package_to_lspconfig), #available_servers)
+    end)
+
+    it("should return all available servers for given filetype", function()
+        assert.same(
+            { "terraformls", "tflint" },
+            _.sort_by(
+                _.identity,
+                mason_lspconfig.get_available_servers {
+                    filetype = "terraform",
+                }
+            )
+        )
+    end)
+
+    it("should return all available servers for given filetypes", function()
+        assert.same(
+            { "lemminx", "taplo" },
+            _.sort_by(
+                _.identity,
+                mason_lspconfig.get_available_servers {
+                    filetype = { "xml", "xsd", "xsl", "toml" },
+                }
+            )
+        )
+    end)
+
+    it("should return no servers if filetype predicate has no matches", function()
+        assert.same(
+            {},
+            mason_lspconfig.get_available_servers {
+                filetype = { "thisfiletypesimplydoesntexist" },
+            }
+        )
+    end)
+end)