fix: avoid calling vim.fn in fast event (#1878)

lua/mason-core/package/init.lua

@@ -7,6 +7,7 @@ local a = require "mason-core.async"
 local fs = require "mason-core.fs"
 local log = require "mason-core.log"
 local path = require "mason-core.path"
+local platform = require "mason-core.platform"
 local registry = require "mason-registry"
 
 local is_not_nil = _.complement(_.is_nil)
@@ -87,7 +88,7 @@ local PackageMt = { __index = Package }
 
 ---@param spec PackageSpec | RegistryPackageSpec
 local function validate_spec(spec)
-    if vim.fn.has "nvim-0.11" ~= 1 then
+    if platform.cached_features["nvim-0.11"] ~= 1 then
         return
     end
     if is_registry_spec(spec) then

lua/mason-core/platform.lua

@@ -66,14 +66,15 @@ end)
 
 -- Most of the code that calls into these functions executes outside of the main event loop, where API/fn functions are
 -- disabled. We evaluate these immediately here to avoid issues with main loop synchronization.
-local cached_features = {
+M.cached_features = {
     ["win"] = vim.fn.has "win32",
     ["win32"] = vim.fn.has "win32",
     ["win64"] = vim.fn.has "win64",
     ["mac"] = vim.fn.has "mac",
     ["darwin"] = vim.fn.has "mac",
     ["unix"] = vim.fn.has "unix",
     ["linux"] = vim.fn.has "linux",
+    ["nvim-0.11"] = vim.fn.has "nvim-0.11",
 }
 
 ---@type fun(env: string): boolean
@@ -104,7 +105,7 @@ local check_env = _.memoize(_.cond {
 M.is = setmetatable({}, {
     __index = function(__, key)
         local os, arch, env = unpack(vim.split(key, "_", { plain = true }))
-        if not cached_features[os] or cached_features[os] ~= 1 then
+        if not M.cached_features[os] or M.cached_features[os] ~= 1 then
             return false
         end
         if arch and arch ~= M.arch then

tests/mason-core/package/package_spec.lua

@@ -193,4 +193,28 @@ describe("package", function()
             end)
         end)
     )
+
+    it(
+        "should be able to instantiate package outside of main loop",
+        async_test(function()
+            local dummy = registry.get_package "registry"
+
+            -- Move outside the main loop
+            a.wait(function(resolve)
+                local timer = vim.loop.new_timer()
+                timer:start(0, 0, function()
+                    timer:close()
+                    resolve()
+                end)
+            end)
+
+            assert.is_true(vim.in_fast_event())
+
+            local pkg = assert.is_not.has_error(function()
+                return Pkg.new(dummy.spec)
+            end)
+
+            assert.same(dummy.spec, pkg.spec)
+        end)
+    )
 end)