feat(filetype): remove side effects from vim.filetype.match (#18894)

Many filetypes from filetype.vim set buffer-local variables, meaning
vim.filetype.match cannot be used without side effects. Instead of
setting these buffer-local variables in the filetype detection functions
themselves, have vim.filetype.match return an optional function value
that, when called, sets these variables. This allows vim.filetype.match
to work without side effects.

1 files changed, 48 insertions, 35 deletions

diff --git a/runtime/lua/vim/filetype/detect.lua b/runtime/lua/vim/filetype/detect.lua
index 2cc75b026e..7e5ed0f4d1 100644
--- a/runtime/lua/vim/filetype/detect.lua
+++ b/runtime/lua/vim/filetype/detect.lua
@@ -27,24 +27,22 @@ local matchregex = vim.filetype.matchregex
 -- This function checks for the kind of assembly that is wanted by the user, or
 -- can be detected from the first five lines of the file.
 function M.asm(bufnr)
-  -- Make sure b:asmsyntax exists
-  if not vim.b[bufnr].asmsyntax then
-    vim.b[bufnr].asmsyntax = ''
-  end
-
-  if vim.b[bufnr].asmsyntax == '' then
-    M.asm_syntax(bufnr)
+  local syntax = vim.b[bufnr].asmsyntax
+  if not syntax or syntax == '' then
+    syntax = M.asm_syntax(bufnr)
   end
 
   -- If b:asmsyntax still isn't set, default to asmsyntax or GNU
-  if vim.b[bufnr].asmsyntax == '' then
+  if not syntax or syntax == '' then
     if vim.g.asmsyntax and vim.g.asmsyntax ~= 0 then
-      vim.b[bufnr].asmsyntax = vim.g.asmsyntax
+      syntax = vim.g.asmsyntax
     else
-      vim.b[bufnr].asmsyntax = 'asm'
+      syntax = 'asm'
     end
   end
-  return vim.fn.fnameescape(vim.b[bufnr].asmsyntax)
+  return syntax, function(b)
+    vim.b[b].asmsyntax = syntax
+  end
 end
 
 -- Checks the first 5 lines for a asmsyntax=foo override.
@@ -53,9 +51,9 @@ function M.asm_syntax(bufnr)
   local lines = table.concat(getlines(bufnr, 1, 5), ' '):lower()
   local match = lines:match('%sasmsyntax=([a-zA-Z0-9]+)%s')
   if match then
-    vim.b['asmsyntax'] = match
+    return match
   elseif findany(lines, { '%.title', '%.ident', '%.macro', '%.subtitle', '%.library' }) then
-    vim.b['asmsyntax'] = 'vmasm'
+    return 'vmasm'
   end
 end
 
@@ -376,12 +374,13 @@ function M.inc(bufnr)
   elseif findany(lines, { '^%s{', '^%s%(%*' }) or matchregex(lines, pascal_keywords) then
     return 'pascal'
   else
-    M.asm_syntax(bufnr)
-    if vim.b[bufnr].asm_syntax then
-      return vim.fn.fnameescape(vim.b[bufnr].asm_syntax)
-    else
+    local syntax = M.asm_syntax(bufnr)
+    if not syntax or syntax == '' then
       return 'pov'
     end
+    return syntax, function(b)
+      vim.b[b].asmsyntax = syntax
+    end
   end
 end
 
@@ -778,6 +777,8 @@ function M.sh(path, bufnr, name)
     return
   end
 
+  local on_detect
+
   if matchregex(name, [[\<csh\>]]) then
     -- Some .sh scripts contain #!/bin/csh.
     return M.shell(path, bufnr, 'csh')
@@ -788,19 +789,25 @@ function M.sh(path, bufnr, name)
   elseif matchregex(name, [[\<zsh\>]]) then
     return M.shell(path, bufnr, 'zsh')
   elseif matchregex(name, [[\<ksh\>]]) then
-    vim.b[bufnr].is_kornshell = 1
-    vim.b[bufnr].is_bash = nil
-    vim.b[bufnr].is_sh = nil
+    on_detect = function(b)
+      vim.b[b].is_kornshell = 1
+      vim.b[b].is_bash = nil
+      vim.b[b].is_sh = nil
+    end
   elseif vim.g.bash_is_sh or matchregex(name, [[\<bash\>]]) or matchregex(name, [[\<bash2\>]]) then
-    vim.b[bufnr].is_bash = 1
-    vim.b[bufnr].is_kornshell = nil
-    vim.b[bufnr].is_sh = nil
+    on_detect = function(b)
+      vim.b[b].is_bash = 1
+      vim.b[b].is_kornshell = nil
+      vim.b[b].is_sh = nil
+    end
   elseif matchregex(name, [[\<sh\>]]) then
-    vim.b[bufnr].is_sh = 1
-    vim.b[bufnr].is_kornshell = nil
-    vim.b[bufnr].is_bash = nil
+    on_detect = function(b)
+      vim.b[b].is_sh = 1
+      vim.b[b].is_kornshell = nil
+      vim.b[b].is_bash = nil
+    end
   end
-  return M.shell(path, bufnr, 'sh')
+  return M.shell(path, bufnr, 'sh'), on_detect
 end
 
 -- For shell-like file types, check for an "exec" command hidden in a comment, as used for Tcl.
@@ -918,9 +925,11 @@ function M.xml(bufnr)
     line = line:lower()
     local is_docbook5 = line:find([[ xmlns="http://docbook.org/ns/docbook"]])
     if is_docbook4 or is_docbook5 then
-      vim.b[bufnr].docbk_type = 'xml'
-      vim.b[bufnr].docbk_ver = is_docbook4 and 4 or 5
-      return 'docbk'
+      return 'docbk',
+        function(b)
+          vim.b[b].docbk_type = 'xml'
+          vim.b[b].docbk_ver = is_docbook4 and 4 or 5
+        end
     end
     if line:find([[xmlns:xbl="http://www.mozilla.org/xbl"]]) then
       return 'xbl'
@@ -954,9 +963,10 @@ function M.sgml(bufnr)
   if lines:find('linuxdoc') then
     return 'smgllnx'
   elseif lines:find('<!DOCTYPE.*DocBook') then
-    vim.b[bufnr].docbk_type = 'sgml'
-    vim.b[bufnr].docbk_ver = 4
-    return 'docbk'
+    return 'docbk', function(b)
+      vim.b[b].docbk_type = 'sgml'
+      vim.b[b].docbk_ver = 4
+    end
   else
     return 'sgml'
   end
@@ -1049,10 +1059,13 @@ end
 -- XFree86 config
 function M.xfree86(bufnr)
   local line = getlines(bufnr, 1)
+  local on_detect
   if matchregex(line, [[\<XConfigurator\>]]) then
-    vim.b[bufnr].xf86conf_xfree86_version = 3
-    return 'xf86conf'
+    on_detect = function(b)
+      vim.b[b].xf86conf_xfree86_version = 3
+    end
   end
+  return 'xf86conf', on_detect
 end
 
 -- luacheck: pop