fix: gf fails on "foo/bar.txt:1:2" on Windows

Problem:
On Windows, "gf" fails on a filepath that has a line:column suffix.
Example:

    E447: Can't find file "src/app/core/services/identity/identity.service.ts:64:23"

Solution:
- Remove ":" from 'isfname' on Windows. Colon is not a valid filename
  character (except for the drive-letter).
- Handle drive letters specially in file_name_in_line().

Fixes #25160

7 files changed, 92 insertions, 8 deletions

diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index f0d01f92e7..2bf912dbfd 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -15,6 +15,9 @@ BREAKING CHANGES                                                *news-breaking*
 
 The following changes may require adaptations in user config or plugins.
 
+• Windows file path drive letters are now detected even if ":" is not in
+  'isfname'. The default 'isfname' no longer includes ":".
+
 • |vim.tbl_islist()| now checks whether a table is actually list-like (i.e.,
   has integer keys without gaps and starting from 1). For the previous
   behavior (only check for integer keys, allow gaps or not starting with 1),
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index bc207d7755..283c1e3612 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3453,7 +3453,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 
 						*'isfname'* *'isf'*
 'isfname' 'isf'		string	(default for Windows:
-                             "@,48-57,/,\,.,-,_,+,,,#,$,%,{,},[,],:,@-@,!,~,="
+                             "@,48-57,/,\,.,-,_,+,,,#,$,%,{,},[,],@-@,!,~,="
                             otherwise: "@,48-57,/,.,-,_,+,,,#,$,%,~,=")
 			global
 	The characters specified by this option are included in file names and
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index e9c04443a6..974aa051cf 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -53,6 +53,8 @@ Defaults					            *nvim-defaults*
 - 'hlsearch' is enabled
 - 'include' defaults to "". The C ftplugin sets it to "^\\s*#\\s*include"
 - 'incsearch' is enabled
+- 'isfname' does not include ":" on Windows. Include ":" in 'isfname' to treat
+  it as part of a filename anywhere in the name (not only the drive letter).
 - 'joinspaces' is disabled
 - 'langnoremap' is enabled
 - 'langremap' is disabled
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index a0b9306908..e70fe8614f 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -4298,9 +4298,9 @@ return {
       defaults = {
         condition = 'BACKSLASH_IN_FILENAME',
         if_false = '@,48-57,/,.,-,_,+,,,#,$,%,~,=',
-        if_true = '@,48-57,/,\\,.,-,_,+,,,#,$,%,{,},[,],:,@-@,!,~,=',
+        if_true = '@,48-57,/,\\,.,-,_,+,,,#,$,%,{,},[,],@-@,!,~,=',
         doc = [[for Windows:
-      "@,48-57,/,\,.,-,_,+,,,#,$,%,{,},[,],:,@-@,!,~,="
+      "@,48-57,/,\,.,-,_,+,,,#,$,%,{,},[,],@-@,!,~,="
      otherwise: "@,48-57,/,.,-,_,+,,,#,$,%,~,="]],
       },
       deny_duplicates = true,
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 41199306fa..ef6d3fd4a9 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -6943,11 +6943,12 @@ char *file_name_in_line(char *line, int col, int options, int count, char *rel_f
   bool is_url = false;
 
   // Search backward for first char of the file name.
-  // Go one char back to ":" before "//" even when ':' is not in 'isfname'.
+  // Go one char back to ":" before "//", or to the drive letter before ":\" (even if ":"
+  // is not in 'isfname').
   while (ptr > line) {
     if ((len = (size_t)(utf_head_off(line, ptr - 1))) > 0) {
       ptr -= len + 1;
-    } else if (vim_isfilec((uint8_t)ptr[-1])
+    } else if (vim_isfilec((uint8_t)ptr[-1]) || path_has_drive_letter(ptr - 2)
                || ((options & FNAME_HYP) && path_is_url(ptr - 1))) {
       ptr--;
     } else {
@@ -6957,14 +6958,13 @@ char *file_name_in_line(char *line, int col, int options, int count, char *rel_f
 
   // Search forward for the last char of the file name.
   // Also allow ":/" when ':' is not in 'isfname'.
-  len = 0;
+  len = path_has_drive_letter(ptr) ? 2 : 0;
   while (vim_isfilec((uint8_t)ptr[len]) || (ptr[len] == '\\' && ptr[len + 1] == ' ')
          || ((options & FNAME_HYP) && path_is_url(ptr + len))
          || (is_url && vim_strchr(":?&=", (uint8_t)ptr[len]) != NULL)) {
     // After type:// we also include :, ?, & and = as valid characters, so that
     // http://google.com:8080?q=this&that=ok works.
-    if ((ptr[len] >= 'A' && ptr[len] <= 'Z')
-        || (ptr[len] >= 'a' && ptr[len] <= 'z')) {
+    if ((ptr[len] >= 'A' && ptr[len] <= 'Z') || (ptr[len] >= 'a' && ptr[len] <= 'z')) {
       if (in_type && path_is_url(ptr + len + 1)) {
         is_url = true;
       }
diff --git a/test/functional/core/path_spec.lua b/test/functional/core/path_spec.lua
index 6c677d76d1..1c6faf8d60 100644
--- a/test/functional/core/path_spec.lua
+++ b/test/functional/core/path_spec.lua
@@ -91,4 +91,80 @@ describe('file search', function()
     feed('gf')
     eq('filename_with_unicode_ααα', eval('expand("%:t")'))
   end)
+
+  it('matches Windows drive-letter filepaths (without ":" in &isfname)', function()
+    local os_win = is_os('win')
+
+    insert([[c:/d:/foo/bar.txt]])
+    eq([[c:/d:/foo/bar.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[//share/c:/foo/bar/]])
+    eq([[//share/c:/foo/bar/]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[file://c:/foo/bar]])
+    eq([[file://c:/foo/bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[https://c:/foo/bar]])
+    eq([[https://c:/foo/bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\foo\bar]])
+    eq(os_win and [[\foo\bar]] or [[bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[/foo/bar]])
+    eq([[/foo/bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[c:\foo\bar]])
+    eq(os_win and [[c:\foo\bar]] or [[bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[c:/foo/bar]])
+    eq([[c:/foo/bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[c:foo\bar]])
+    eq(os_win and [[foo\bar]] or [[bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[c:foo/bar]])
+    eq([[foo/bar]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[c:foo]])
+    eq([[foo]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    -- Examples from: https://learn.microsoft.com/en-us/dotnet/standard/io/file-path-formats#example-ways-to-refer-to-the-same-file
+    insert([[c:\temp\test-file.txt]])
+    eq(os_win and [[c:\temp\test-file.txt]] or [[test-file.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\\127.0.0.1\c$\temp\test-file.txt]])
+    eq(os_win and [[\\127.0.0.1\c$\temp\test-file.txt]] or [[test-file.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\\LOCALHOST\c$\temp\test-file.txt]])
+    eq(os_win and [[\\LOCALHOST\c$\temp\test-file.txt]] or [[test-file.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\\.\c:\temp\test-file.txt]]) -- not supported yet
+    eq(os_win and [[\\.\c]] or [[test-file.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\\?\c:\temp\test-file.txt]]) -- not supported yet
+    eq(os_win and [[\c]] or [[test-file.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\\.\UNC\LOCALHOST\c$\temp\test-file.txt]])
+    eq(os_win and [[\\.\UNC\LOCALHOST\c$\temp\test-file.txt]] or [[test-file.txt]], eval('expand("<cfile>")'))
+    command('%delete')
+
+    insert([[\\127.0.0.1\c$\temp\test-file.txt]])
+    eq(os_win and [[\\127.0.0.1\c$\temp\test-file.txt]] or [[test-file.txt]], eval('expand("<cfile>")'))
+  end)
 end)
diff --git a/test/old/testdir/setup.vim b/test/old/testdir/setup.vim
index 096ddba40b..b0c2a15a3f 100644
--- a/test/old/testdir/setup.vim
+++ b/test/old/testdir/setup.vim
@@ -26,6 +26,9 @@ if exists('s:did_load')
   set sessionoptions+=options
   set viewoptions+=options
   set switchbuf=
+  if has('win32')
+    set isfname+=:
+  endif
   if g:testname !~ 'test_mapping.vim$'
     " Make "Q" switch to Ex mode.
     " This does not work for all tests.