vim-patch:9.0.1773: cannot distinguish Forth and Fortran *.f files (#24841)

Problem:  cannot distinguish Forth and Fortran *.f files
Solution: Add Filetype detection Code

Also add *.4th as a Forth filetype

closes: vim/vim#12251

https://github.com/vim/vim/commit/19a3bc3addf9b4aa8150a01b11b4249c67d15d3b

Don't remove filetype files from Vim patches:
- filetype.vim, script.vim, ft.vim usually contain useful changes
- script.vim and ft.vim don't even have their paths spelled correctly

Co-authored-by: Doug Kearns <dougkearns@gmail.com>

6 files changed, 108 insertions, 15 deletions

diff --git a/runtime/doc/filetype.txt b/runtime/doc/filetype.txt
index 9ebdc71eb2..cf60ecdb6b 100644
--- a/runtime/doc/filetype.txt
+++ b/runtime/doc/filetype.txt
@@ -144,6 +144,7 @@ variables can be used to overrule the filetype used for certain extensions:
 	`*.cls`		g:filetype_cls
 	`*.csh`		g:filetype_csh	|ft-csh-syntax|
 	`*.dat`		g:filetype_dat
+	`*.f`		g:filetype_f	|ft-forth-syntax|
 	`*.frm`		g:filetype_frm	|ft-form-syntax|
 	`*.fs`		g:filetype_fs	|ft-forth-syntax|
 	`*.i`		g:filetype_i	|ft-progress-syntax|
diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 498c55389a..59f8235ad2 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -1542,9 +1542,10 @@ example, FORM files, use this in your startup vimrc: >
 
 FORTH						*forth.vim* *ft-forth-syntax*
 
-Files matching "*.fs" could be F# or Forth.  If the automatic detection
-doesn't work for you, or you don't edit F# at all, use this in your
-startup vimrc: >
+Files matching "*.f" could be Fortran or Forth and those matching "*.fs" could
+be F# or Forth.  If the automatic detection doesn't work for you, or you don't
+edit F# or Fortran at all, use this in your startup vimrc: >
+   :let filetype_f  = "forth"
    :let filetype_fs = "forth"
 
 
diff --git a/runtime/lua/vim/filetype.lua b/runtime/lua/vim/filetype.lua
index ffb284cca7..c310eb3e42 100644
--- a/runtime/lua/vim/filetype.lua
+++ b/runtime/lua/vim/filetype.lua
@@ -398,6 +398,7 @@ local extension = {
   EXW = detect.euphoria,
   ex = detect.ex,
   exp = 'expect',
+  f = detect.f,
   factor = 'factor',
   fal = 'falcon',
   fan = 'fan',
@@ -410,8 +411,9 @@ local extension = {
   fish = 'fish',
   focexec = 'focexec',
   fex = 'focexec',
-  fth = 'forth',
   ft = 'forth',
+  fth = 'forth',
+  ['4th'] = 'forth',
   FOR = 'fortran',
   f77 = 'fortran',
   f03 = 'fortran',
@@ -427,7 +429,6 @@ local extension = {
   F77 = 'fortran',
   f95 = 'fortran',
   FPP = 'fortran',
-  f = 'fortran',
   F = 'fortran',
   F08 = 'fortran',
   f08 = 'fortran',
diff --git a/runtime/lua/vim/filetype/detect.lua b/runtime/lua/vim/filetype/detect.lua
index 59b50f2288..4a7a1cbefe 100644
--- a/runtime/lua/vim/filetype/detect.lua
+++ b/runtime/lua/vim/filetype/detect.lua
@@ -473,6 +473,38 @@ function M.ex(_, bufnr)
   end
 end
 
+--- @param bufnr integer
+--- @return boolean
+local function is_forth(bufnr)
+  local first_line = nextnonblank(bufnr, 1)
+
+  -- SwiftForth block comment (line is usually filled with '-' or '=') or
+  -- OPTIONAL (sometimes precedes the header comment)
+  if first_line and findany(first_line:lower(), { '^%{%s', '^%{$', '^optional%s' }) then
+    return true
+  end
+
+  for _, line in ipairs(getlines(bufnr, 1, 100)) do
+    -- Forth comments and colon definitions
+    if line:find('^[:(\\] ') then
+      return true
+    end
+  end
+  return false
+end
+
+-- Distinguish between Forth and Fortran
+--- @type vim.filetype.mapfn
+function M.f(_, bufnr)
+  if vim.g.filetype_f then
+    return vim.g.filetype_f
+  end
+  if is_forth(bufnr) then
+    return 'forth'
+  end
+  return 'fortran'
+end
+
 -- This function checks the first 15 lines for appearance of 'FoamFile'
 -- and then 'object' in a following line.
 -- In that case, it's probably an OpenFOAM file
@@ -518,16 +550,14 @@ function M.fvwm_v2(path, _)
   end
 end
 
--- Distinguish between Forth and F#.
+-- Distinguish between Forth and F#
 --- @type vim.filetype.mapfn
 function M.fs(_, bufnr)
   if vim.g.filetype_fs then
     return vim.g.filetype_fs
   end
-  for _, line in ipairs(getlines(bufnr, 1, 100)) do
-    if line:find('^[:(\\] ') then
-      return 'forth'
-    end
+  if is_forth(bufnr) then
+    return 'forth'
   end
   return 'fsharp'
 end
diff --git a/scripts/vim-patch.sh b/scripts/vim-patch.sh
index 3f411dac49..af73a8006a 100755
--- a/scripts/vim-patch.sh
+++ b/scripts/vim-patch.sh
@@ -202,9 +202,9 @@ preprocess_patch() {
   local na_src='auto\|configure.*\|GvimExt\|hardcopy.*\|libvterm\|proto\|tee\|VisVim\|xpm\|xxd\|Make.*\|INSTALL.*\|beval.*\|gui.*\|if_cscop\|if_lua\|if_mzsch\|if_olepp\|if_ole\|if_perl\|if_py\|if_ruby\|if_tcl\|if_xcmdsrv'
   2>/dev/null $nvim --cmd 'set dir=/tmp' +'g@^diff --git a/src/\S*\<\%(testdir/\)\@<!\%('"${na_src}"'\)\>@norm! d/\v(^diff)|%$
' +w +q "$file"
 
-  # Remove runtime files ported to Lua.
-  local na_rt='filetype\.vim\|scripts\.vim\|autoload\/ft\/dist\.vim\|print\/.*'
-  2>/dev/null $nvim --cmd 'set dir=/tmp' +'g@^diff --git a/runtime/\<\%('"${na_rt}"'\)\>@norm! d/\v(^diff)|%$
' +w +q "$file"
+  # Remove runtime/print/
+  local na_rt='print\/.*'
+  2>/dev/null $nvim --cmd 'set dir=/tmp' +'g@^diff --git a/runtime/\<\%('"${na_rt}"'\)\>@norm! d/\v(^diff)|%$' +w +q "$file"
 
   # Remove unwanted Vim doc files.
   local na_doc='channel\.txt\|if_cscop\.txt\|netbeans\.txt\|os_\w\+\.txt\|print\.txt\|term\.txt\|todo\.txt\|version\d\.txt\|vim9\.txt\|sponsor\.txt\|intro\.txt\|tags'
diff --git a/test/old/testdir/test_filetype.vim b/test/old/testdir/test_filetype.vim
index f11c0ffc31..3ce8e49b27 100644
--- a/test/old/testdir/test_filetype.vim
+++ b/test/old/testdir/test_filetype.vim
@@ -236,7 +236,7 @@ func s:GetFilenameChecks() abort
     \ 'fish': ['file.fish'],
     \ 'focexec': ['file.fex', 'file.focexec'],
     \ 'form': ['file.frm'],
-    \ 'forth': ['file.ft', 'file.fth'],
+    \ 'forth': ['file.ft', 'file.fth', 'file.4th'],
     \ 'fortran': ['file.f', 'file.for', 'file.fortran', 'file.fpp', 'file.ftn', 'file.f77', 'file.f90', 'file.f95', 'file.f03', 'file.f08'],
     \ 'fpcmake': ['file.fpc'],
     \ 'framescript': ['file.fsl'],
@@ -1173,6 +1173,54 @@ func Test_ex_file()
   filetype off
 endfunc
 
+func Test_f_file()
+  filetype on
+
+  call writefile(['looks like Fortran'], 'Xfile.f', 'D')
+  split Xfile.f
+  call assert_equal('fortran', &filetype)
+  bwipe!
+
+  let g:filetype_f = 'forth'
+  split Xfile.f
+  call assert_equal('forth', &filetype)
+  bwipe!
+  unlet g:filetype_f
+
+  " Test dist#ft#FTf()
+
+  " Forth
+
+  call writefile(['( Forth inline comment )'], 'Xfile.f')
+  split Xfile.f
+  call assert_equal('forth', &filetype)
+  bwipe!
+
+  call writefile(['\ Forth line comment'], 'Xfile.f')
+  split Xfile.f
+  call assert_equal('forth', &filetype)
+  bwipe!
+
+  call writefile([': squared ( n -- n^2 )', 'dup * ;'], 'Xfile.f')
+  split Xfile.f
+  call assert_equal('forth', &filetype)
+  bwipe!
+
+  " SwiftForth
+
+  call writefile(['{ ================', 'Header comment', '================ }'], 'Xfile.f')
+  split Xfile.f
+  call assert_equal('forth', &filetype)
+  bwipe!
+
+  call writefile(['OPTIONAL Maybe Descriptive text'], 'Xfile.f')
+  split Xfile.f
+  call assert_equal('forth', &filetype)
+  bwipe!
+
+  filetype off
+endfunc
+
 func Test_foam_file()
   filetype on
   call assert_true(mkdir('0', 'pR'))
@@ -1263,7 +1311,7 @@ func Test_fs_file()
 
   " Test dist#ft#FTfs()
 
-  " Forth (Gforth)
+  " Forth
 
   call writefile(['( Forth inline comment )'], 'Xfile.fs')
   split Xfile.fs
@@ -1280,6 +1328,18 @@ func Test_fs_file()
   call assert_equal('forth', &filetype)
   bwipe!
 
+  " SwiftForth
+
+  call writefile(['{ ================', 'Header comment', '================ }'], 'Xfile.fs')
+  split Xfile.fs
+  call assert_equal('forth', &filetype)
+  bwipe!
+
+  call writefile(['OPTIONAL Maybe Descriptive text'], 'Xfile.fs')
+  split Xfile.fs
+  call assert_equal('forth', &filetype)
+  bwipe!
+
   filetype off
 endfunc