perf: host pre-compiled filetype mappings (#555)

Generating the filetype mappings by accessing `vim.lsp.config` turns out to be a bad idea because:
1) performance
2) some `lsp/` configurations in nvim-lspconfig execute code immediately (see angularls)
3) accessing `vim.lsp.config[server_name]` seems to populate `:checkhealth vim.lsp`

2 files changed, 82 insertions, 0 deletions

diff --git a/scripts/lua/mason-scripts/mason-lspconfig/generate.lua b/scripts/lua/mason-scripts/mason-lspconfig/generate.lua
new file mode 100644
index 0000000..75584aa
--- /dev/null
+++ b/scripts/lua/mason-scripts/mason-lspconfig/generate.lua
@@ -0,0 +1,42 @@
+local Optional = require "mason-core.optional"
+
+local _ = require "mason-core.functional"
+local a = require "mason-core.async"
+local path = require "mason-core.path"
+local script_utils = require "mason-scripts.utils"
+
+local MASON_LSPCONFIG_DIR = path.concat { "lua", "mason-lspconfig" }
+
+require("mason").setup()
+local registry = require "mason-registry"
+registry.refresh()
+
+---@async
+local function create_lspconfig_filetype_map()
+    local lspconfig_servers =
+        _.filter_map(_.compose(Optional.of_nilable, _.path { "neovim", "lspconfig" }), registry.get_all_package_specs())
+    ---@type table<string, string[]>
+    local filetype_map = {}
+
+    for _, server_name in ipairs(lspconfig_servers) do
+        local filetypes = vim.tbl_get(vim.lsp.config, server_name, "filetypes")
+        if filetypes then
+            for _, filetype in ipairs(filetypes) do
+                if not filetype_map[filetype] then
+                    filetype_map[filetype] = {}
+                end
+                table.insert(filetype_map[filetype], server_name)
+            end
+        end
+    end
+
+    script_utils.write_file(
+        path.concat { MASON_LSPCONFIG_DIR, "filetype_mappings.lua" },
+        "return " .. vim.inspect(filetype_map),
+        "w"
+    )
+end
+
+a.run_blocking(function()
+    create_lspconfig_filetype_map()
+end)
diff --git a/scripts/lua/mason-scripts/utils.lua b/scripts/lua/mason-scripts/utils.lua
new file mode 100644
index 0000000..ee6ab10
--- /dev/null
+++ b/scripts/lua/mason-scripts/utils.lua
@@ -0,0 +1,40 @@
+local _ = require "mason-core.functional"
+local fs = require "mason-core.fs"
+
+local M = {}
+
+---@async
+---@param path string
+---@param contents string
+---@param flags string?
+function M.write_file(path, contents, flags)
+    local header = _.cond({
+        {
+            _.matches "%.lua$",
+            _.always {
+                "-- THIS FILE IS GENERATED. DO NOT EDIT MANUALLY.",
+                "-- stylua: ignore start",
+            },
+        },
+        {
+            _.matches "%.md$",
+            _.always {
+                "<!--- THIS FILE IS GENERATED. DO NOT EDIT MANUALLY. -->",
+            },
+        },
+        {
+            _.matches "doc/.+%.txt$",
+            _.always {},
+        },
+        {
+            _.T,
+            _.always {
+                "# THIS FILE IS GENERATED. DO NOT EDIT MANUALLY.",
+            },
+        },
+    }, path)
+
+    fs.async.write_file(path, table.concat(_.concat(header, { contents }), "\n"), flags)
+end
+
+return M