feat(eval): mark getenv() as api-fast #42703

Problem:
`vim.env` (`vim.fn.getenv`) fails in a fast context (luv callbacks, LSP
rpc).

Solution:
Mark `getenv()` as |api-fast|. `vim_getenv()` never tickles `os_breakcheck()`.

runtime/doc/news.txt

@@ -575,10 +575,10 @@ VIMSCRIPT
 • |v:useractive| indicates user activity.
 • |serverlist()| with `info=true` returns details for each server (own + peers).
 • These Vimscript functions may be called from |api-fast| context (e.g.
-  |vim.uv| timer/handle callbacks): |keytrans()|, |char2nr()|, |nr2char()|,
-  |str2list()|, |strpart()|, |strcharpart()|, |strgetchar()|, |strchars()|,
-  |strcharlen()|, |strlen()|, |strdisplaywidth()|, |byteidx()|, |charidx()|,
-  |utf16idx()|, |tr()|, |trim()|.
+  |vim.uv| timer/handle callbacks): |getenv()|, |keytrans()|, |char2nr()|,
+  |nr2char()|, |str2list()|, |strpart()|, |strcharpart()|, |strgetchar()|,
+  |strchars()|, |strcharlen()|, |strlen()|, |strdisplaywidth()|, |byteidx()|,
+  |charidx()|, |utf16idx()|, |tr()|, |trim()|.
 
 ==============================================================================
 CHANGED FEATURES                                                 *news-changed*

runtime/doc/vimfn.txt

@@ -3816,6 +3816,9 @@ getenv({name})                                                        *getenv()*
 		is different from a variable set to an empty string.
 		See also |expr-env|.
 
+                Attributes: ~
+                  |api-fast|
+
                 Parameters: ~
                   • {name} (`string`)
 

runtime/lua/vim/log.lua

@@ -102,8 +102,7 @@ local function default_format_func(min_level, level, ...)
   local info = debug.getinfo(3, 'Sl')
   -- Full path (`short_src` is truncated), with $VIMRUNTIME abbreviated.
   local src = info and (info.source:match('^@(.*)') or info.short_src) or '?'
-  local vimruntime = vim.uv.os_getenv('VIMRUNTIME') -- Use `vim.uv` for api-fast (e.g. LSP rpc).
-  local rt_path = vimruntime and vim.fs.relpath(vimruntime, src)
+  local rt_path = vim.env.VIMRUNTIME and vim.fs.relpath(vim.env.VIMRUNTIME, src)
   local header = string.format(
     '[%s][%s] %s:%s',
     level_names[level],

src/nvim/eval.lua

@@ -4161,6 +4161,7 @@ M.funcs = {
       See also |expr-env|.
 
     ]=],
+    fast = true,
     name = 'getenv',
     params = { { 'name', 'string' } },
     returns = 'string',

test/functional/api/fast_spec.lua

@@ -12,6 +12,7 @@ describe('|api-fast| functions', function()
   it('callable in a fast event', function()
     local out = exec_lua(function()
       local result
+      vim.uv.os_setenv('XTEST_FAST', 'x')
       local timer = assert(vim.uv.new_timer())
       timer:start(0, 0, function()
         timer:close()
@@ -21,6 +22,7 @@ describe('|api-fast| functions', function()
             byteidx = vim.fn.byteidx('héllo', 2),
             char2nr = vim.fn.char2nr('A'),
             charidx = vim.fn.charidx('héllo', 3),
+            getenv = vim.env.XTEST_FAST,
             in_fast = vim.in_fast_event(),
             keycode = vim.keycode('<C-a>'),
             keytrans = vim.fn.keytrans(vim.keycode('<C-Home>')),
@@ -55,6 +57,7 @@ describe('|api-fast| functions', function()
       byteidx = 3,
       char2nr = 65,
       charidx = 2,
+      getenv = 'x',
       in_fast = true,
       keycode = '\1', -- <C-a>
       keytrans = '<C-Home>',
@@ -108,6 +111,11 @@ describe('|api-fast| functions', function()
         charidx = function()
           vim.fn.charidx(big, 500000)
         end,
+        getenv = function()
+          -- Unset, so getenv() computes it.
+          vim.env.VIMRUNTIME = nil
+          vim.fn.getenv('VIMRUNTIME')
+        end,
         keycode = function()
           vim.keycode('<C-a>')
         end,