vim-patch:8.2.3900: it is not easy to use a script-local function for an option

Problem:    It is not easy to use a script-local function for an option.
Solution:   recognize s: and <SID> at the start of the expression. (Yegappan
            Lakshmanan, closes vim/vim#9401)

https://github.com/vim/vim/commit/8bb65f230d3025037f34021a72616038da0601ee

Omit duplicate docs in fold.txt: removed in a later runtime update.
Cherry-pick test_diffmode.vim changes from patch 8.2.1432.

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

13 files changed, 215 insertions, 9 deletions

diff --git a/runtime/doc/diff.txt b/runtime/doc/diff.txt
index b5a3891d3f..f38f123393 100644
--- a/runtime/doc/diff.txt
+++ b/runtime/doc/diff.txt
@@ -388,6 +388,11 @@ mode, so that a CTRL-Z doesn't end the text on DOS.
 The `redraw!` command may not be needed, depending on whether executing a
 shell command shows something on the display or not.
 
+If the 'diffexpr' expression starts with s: or |<SID>|, then it is replaced
+with the script ID (|local-function|). Example: >
+		set diffexpr=s:MyDiffExpr()
+		set diffexpr=<SID>SomeDiffExpr()
+<
 						*E810* *E97*
 Vim will do a test if the diff output looks alright.  If it doesn't, you will
 get an error message.  Possible causes:
@@ -439,4 +444,9 @@ evaluating 'patchexpr'.  This hopefully avoids that files in the current
 directory are accidentally patched.  Vim will also delete files starting with
 v:fname_in and ending in ".rej" and ".orig".
 
+If the 'patchexpr' expression starts with s: or |<SID>|, then it is replaced
+with the script ID (|local-function|). Example: >
+		set patchexpr=s:MyPatchExpr()
+		set patchexpr=<SID>SomePatchExpr()
+<
  vim:tw=78:ts=8:noet:ft=help:norl:
diff --git a/runtime/doc/fold.txt b/runtime/doc/fold.txt
index e97a0a6459..04c5b70c45 100644
--- a/runtime/doc/fold.txt
+++ b/runtime/doc/fold.txt
@@ -116,6 +116,11 @@ method can be very slow!
 Try to avoid the "=", "a" and "s" return values, since Vim often has to search
 backwards for a line for which the fold level is defined.  This can be slow.
 
+If the 'foldexpr' expression starts with s: or |<SID>|, then it is replaced
+with the script ID (|local-function|). Example: >
+		set foldexpr=s:MyFoldExpr()
+		set foldexpr=<SID>SomeFoldExpr()
+<
 An example of using "a1" and "s1": For a multi-line C comment, a line
 containing "/*" would return "a1" to start a fold, and a line containing "*/"
 would return "s1" to end the fold after that line: >
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 33bade3545..7edc965941 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -2738,6 +2738,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 	When the expression evaluates to non-zero Vim will fall back to using
 	the internal format mechanism.
 
+	If the expression starts with s: or |<SID>|, then it is replaced with
+	the script ID (|local-function|). Example: >
+		set formatexpr=s:MyFormatExpr()
+		set formatexpr=<SID>SomeFormatExpr()
+<
 	The expression will be evaluated in the |sandbox| when set from a
 	modeline, see |sandbox-option|.  That stops the option from working,
 	since changing the buffer text is not allowed.
@@ -3362,6 +3367,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 	found.  Allows doing "gf" on the name after an 'include' statement.
 	Also used for |<cfile>|.
 
+	If the expression starts with s: or |<SID>|, then it is replaced with
+	the script ID (|local-function|). Example: >
+		set includeexpr=s:MyIncludeExpr(v:fname)
+		set includeexpr=<SID>SomeIncludeExpr(v:fname)
+<
 	The expression will be evaluated in the |sandbox| when set from a
 	modeline, see |sandbox-option|.
 	This option cannot be set in a modeline when 'modelineexpr' is off.
@@ -3417,6 +3427,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 	The expression is evaluated with |v:lnum| set to the line number for
 	which the indent is to be computed.  The cursor is also in this line
 	when the expression is evaluated (but it may be moved around).
+	If the expression starts with s: or |<SID>|, then it is replaced with
+	the script ID (|local-function|). Example: >
+		set indentexpr=s:MyIndentExpr()
+		set indentexpr=<SID>SomeIndentExpr()
+<
 	The expression must return the number of spaces worth of indent.  It
 	can return "-1" to keep the current indent (this means 'autoindent' is
 	used for the indent).
diff --git a/runtime/doc/print.txt b/runtime/doc/print.txt
index e24b6b0347..ef3e47d32c 100644
--- a/runtime/doc/print.txt
+++ b/runtime/doc/print.txt
@@ -155,6 +155,11 @@ an error message.  In that case Vim will delete the file.  In the default
 value for non-MS-Windows a trick is used: Adding "v:shell_error" will result
 in a non-zero number when the system() call fails.
 
+If the expression starts with s: or |<SID>|, then it is replaced with the
+script ID (|local-function|). Example: >
+		set printexpr=s:MyPrintFile()
+		set printexpr=<SID>SomePrintFile()
+<
 This option cannot be set from a |modeline| or in the |sandbox|, for security
 reasons.
 
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index fdb379a682..554771d9c9 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -711,7 +711,7 @@ void eval_patch(const char *const origfile, const char *const difffile, const ch
   set_vim_var_string(VV_FNAME_IN, origfile, -1);
   set_vim_var_string(VV_FNAME_DIFF, difffile, -1);
   set_vim_var_string(VV_FNAME_OUT, outfile, -1);
-  (void)eval_to_bool((char *)p_pex, &err, NULL, false);
+  (void)eval_to_bool(p_pex, &err, NULL, false);
   set_vim_var_string(VV_FNAME_IN, NULL, -1);
   set_vim_var_string(VV_FNAME_DIFF, NULL, -1);
   set_vim_var_string(VV_FNAME_OUT, NULL, -1);
diff --git a/src/nvim/option_defs.h b/src/nvim/option_defs.h
index 40ce022bea..de07327416 100644
--- a/src/nvim/option_defs.h
+++ b/src/nvim/option_defs.h
@@ -622,7 +622,7 @@ EXTERN char *p_opfunc;          // 'operatorfunc'
 EXTERN char_u *p_para;          // 'paragraphs'
 EXTERN int p_paste;             // 'paste'
 EXTERN char *p_pt;              // 'pastetoggle'
-EXTERN char_u *p_pex;           // 'patchexpr'
+EXTERN char *p_pex;             // 'patchexpr'
 EXTERN char *p_pm;              // 'patchmode'
 EXTERN char_u *p_path;          // 'path'
 EXTERN char_u *p_cdpath;        // 'cdpath'
diff --git a/src/nvim/optionstr.c b/src/nvim/optionstr.c
index 61a51532a4..b5dce7ff2a 100644
--- a/src/nvim/optionstr.c
+++ b/src/nvim/optionstr.c
@@ -17,6 +17,7 @@
 #include "nvim/drawscreen.h"
 #include "nvim/eval.h"
 #include "nvim/eval/typval_defs.h"
+#include "nvim/eval/userfunc.h"
 #include "nvim/eval/vars.h"
 #include "nvim/ex_getln.h"
 #include "nvim/fold.h"
@@ -1341,10 +1342,6 @@ char *did_set_string_option(int opt_idx, char **varp, char *oldval, char *errbuf
         newFoldLevel();
       }
     }
-  } else if (varp == &curwin->w_p_fde) {  // 'foldexpr'
-    if (foldmethodIsExpr(curwin)) {
-      foldUpdateAll(curwin);
-    }
   } else if (gvarp == &curwin->w_allbuf_opt.wo_fmr) {  // 'foldmarker'
     p = vim_strchr(*varp, ',');
     if (p == NULL) {
@@ -1484,6 +1481,51 @@ char *did_set_string_option(int opt_idx, char **varp, char *oldval, char *errbuf
         }
       }
     }
+  } else if (varp == &p_dex
+             || varp == &curwin->w_p_fde
+             || gvarp == &p_fex
+             || gvarp == &p_inex
+             || gvarp == &p_inde
+             || varp == &p_pex
+             || varp == &p_pexpr) {  // '*expr' options
+    char **p_opt = NULL;
+
+    // If the option value starts with <SID> or s:, then replace that with
+    // the script identifier.
+
+    if (varp == &p_dex) {  // 'diffexpr'
+      p_opt = &p_dex;
+    }
+    if (varp == &curwin->w_p_fde) {  // 'foldexpr'
+      p_opt = &curwin->w_p_fde;
+    }
+    if (gvarp == &p_fex) {  // 'formatexpr'
+      p_opt = &curbuf->b_p_fex;
+    }
+    if (gvarp == &p_inex) {  // 'includeexpr'
+      p_opt = &curbuf->b_p_inex;
+    }
+    if (gvarp == &p_inde) {  // 'indentexpr'
+      p_opt = &curbuf->b_p_inde;
+    }
+    if (varp == &p_pex) {  // 'patchexpr'
+      p_opt = &p_pex;
+    }
+    if (varp == &p_pexpr) {  // 'printexpr'
+      p_opt = &p_pexpr;
+    }
+
+    if (p_opt != NULL) {
+      char *name = get_scriptlocal_funcname(*p_opt);
+      if (name != NULL) {
+        free_string_option(*p_opt);
+        *p_opt = name;
+      }
+    }
+
+    if (varp == &curwin->w_p_fde && foldmethodIsExpr(curwin)) {
+      foldUpdateAll(curwin);
+    }
   } else if (gvarp == &p_cfu) {  // 'completefunc'
     if (set_completefunc_option() == FAIL) {
       errmsg = e_invarg;
diff --git a/src/nvim/testdir/test_diffmode.vim b/src/nvim/testdir/test_diffmode.vim
index d83cd505a6..0049398776 100644
--- a/src/nvim/testdir/test_diffmode.vim
+++ b/src/nvim/testdir/test_diffmode.vim
@@ -1,4 +1,5 @@
 " Tests for diff mode
+
 source shared.vim
 source screendump.vim
 source check.vim
@@ -681,15 +682,25 @@ func Test_diffexpr()
   set diffexpr=NewDiffFunc()
   call assert_fails('windo diffthis', ['E117:', 'E97:'])
   diffoff!
+
+  " Using a script-local function
+  func s:NewDiffExpr()
+  endfunc
+  set diffexpr=s:NewDiffExpr()
+  call assert_equal(expand('<SID>') .. 'NewDiffExpr()', &diffexpr)
+  set diffexpr=<SID>NewDiffExpr()
+  call assert_equal(expand('<SID>') .. 'NewDiffExpr()', &diffexpr)
+
   %bwipe!
   set diffexpr& diffopt&
+  delfunc DiffExpr
+  delfunc s:NewDiffExpr
 endfunc
 
 func Test_diffpatch()
   " The patch program on MS-Windows may fail or hang.
-  if !executable('patch') || !has('unix')
-    return
-  endif
+  CheckExecutable patch
+  CheckUnix
   new
   insert
 ***************
@@ -1250,10 +1261,19 @@ func Test_patchexpr()
   call assert_equal(2, winnr('$'))
   call assert_true(&diff)
 
+  " Using a script-local function
+  func s:NewPatchExpr()
+  endfunc
+  set patchexpr=s:NewPatchExpr()
+  call assert_equal(expand('<SID>') .. 'NewPatchExpr()', &patchexpr)
+  set patchexpr=<SID>NewPatchExpr()
+  call assert_equal(expand('<SID>') .. 'NewPatchExpr()', &patchexpr)
+
   call delete('Xinput')
   call delete('Xdiff')
   set patchexpr&
   delfunc TPatch
+  delfunc s:NewPatchExpr
   %bwipe!
 endfunc
 
diff --git a/src/nvim/testdir/test_edit.vim b/src/nvim/testdir/test_edit.vim
index 89e597f401..fd54f77ccb 100644
--- a/src/nvim/testdir/test_edit.vim
+++ b/src/nvim/testdir/test_edit.vim
@@ -330,6 +330,16 @@ func Test_edit_11_indentexpr()
   set cinkeys&vim indentkeys&vim
   set nocindent indentexpr=
   delfu Do_Indent
+
+  " Using a script-local function
+  func s:NewIndentExpr()
+  endfunc
+  set indentexpr=s:NewIndentExpr()
+  call assert_equal(expand('<SID>') .. 'NewIndentExpr()', &indentexpr)
+  set indentexpr=<SID>NewIndentExpr()
+  call assert_equal(expand('<SID>') .. 'NewIndentExpr()', &indentexpr)
+  set indentexpr&
+
   bw!
 endfunc
 
diff --git a/src/nvim/testdir/test_fold.vim b/src/nvim/testdir/test_fold.vim
index 2215166cd6..bc8364a80e 100644
--- a/src/nvim/testdir/test_fold.vim
+++ b/src/nvim/testdir/test_fold.vim
@@ -1273,6 +1273,32 @@ func Test_fold_jump()
   bw!
 endfunc
 
+" Test for using a script-local function for 'foldexpr'
+func Test_foldexpr_scriptlocal_func()
+  func! s:FoldFunc()
+    let g:FoldLnum = v:lnum
+  endfunc
+  new | only
+  call setline(1, 'abc')
+  let g:FoldLnum = 0
+  set foldmethod=expr foldexpr=s:FoldFunc()
+  redraw!
+  call assert_equal(expand('<SID>') .. 'FoldFunc()', &foldexpr)
+  call assert_equal(1, g:FoldLnum)
+  set foldmethod& foldexpr=
+  bw!
+  new | only
+  call setline(1, 'abc')
+  let g:FoldLnum = 0
+  set foldmethod=expr foldexpr=<SID>FoldFunc()
+  redraw!
+  call assert_equal(expand('<SID>') .. 'FoldFunc()', &foldexpr)
+  call assert_equal(1, g:FoldLnum)
+  set foldmethod& foldexpr=
+  delfunc s:FoldFunc
+  bw!
+endfunc
+
 " Make sure a fold containing a nested fold is split correctly when using
 " foldmethod=indent
 func Test_fold_split()
diff --git a/src/nvim/testdir/test_gf.vim b/src/nvim/testdir/test_gf.vim
index b2bb189688..e369645328 100644
--- a/src/nvim/testdir/test_gf.vim
+++ b/src/nvim/testdir/test_gf.vim
@@ -226,6 +226,32 @@ func Test_gf_includeexpr()
   delfunc IncFunc
 endfunc
 
+" Test for using a script-local function for 'includeexpr'
+func Test_includeexpr_scriptlocal_func()
+  func! s:IncludeFunc()
+    let g:IncludeFname = v:fname
+    return ''
+  endfunc
+  set includeexpr=s:IncludeFunc()
+  call assert_equal(expand('<SID>') .. 'IncludeFunc()', &includeexpr)
+  new | only
+  call setline(1, 'TestFile1')
+  let g:IncludeFname = ''
+  call assert_fails('normal! gf', 'E447:')
+  call assert_equal('TestFile1', g:IncludeFname)
+  bw!
+  set includeexpr=<SID>IncludeFunc()
+  call assert_equal(expand('<SID>') .. 'IncludeFunc()', &includeexpr)
+  new | only
+  call setline(1, 'TestFile2')
+  let g:IncludeFname = ''
+  call assert_fails('normal! gf', 'E447:')
+  call assert_equal('TestFile2', g:IncludeFname)
+  set includeexpr&
+  delfunc s:IncludeFunc
+  bw!
+endfunc
+
 " Check that expanding directories can handle more than 255 entries.
 func Test_gf_subdirs_wildcard()
   let cwd = getcwd()
diff --git a/src/nvim/testdir/test_hardcopy.vim b/src/nvim/testdir/test_hardcopy.vim
index e390bd5cc8..be83728b4f 100644
--- a/src/nvim/testdir/test_hardcopy.vim
+++ b/src/nvim/testdir/test_hardcopy.vim
@@ -125,6 +125,14 @@ func Test_printexpr()
   set printexpr=PrintFails(v:fname_in)
   call assert_fails('hardcopy', 'E365:')
 
+  " Using a script-local function
+  func s:NewPrintExpr()
+  endfunc
+  set printexpr=s:NewPrintExpr()
+  call assert_equal(expand('<SID>') .. 'NewPrintExpr()', &printexpr)
+  set printexpr=<SID>NewPrintExpr()
+  call assert_equal(expand('<SID>') .. 'NewPrintExpr()', &printexpr)
+
   set printexpr&
   bwipe
 endfunc
diff --git a/src/nvim/testdir/test_normal.vim b/src/nvim/testdir/test_normal.vim
index 9c5cc51f79..7e8b8c5eef 100644
--- a/src/nvim/testdir/test_normal.vim
+++ b/src/nvim/testdir/test_normal.vim
@@ -255,6 +255,45 @@ func Test_normal_formatexpr_returns_nonzero()
   close!
 endfunc
 
+" Test for using a script-local function for 'formatexpr'
+func Test_formatexpr_scriptlocal_func()
+  func! s:Format()
+    let g:FormatArgs = [v:lnum, v:count]
+  endfunc
+  set formatexpr=s:Format()
+  call assert_equal(expand('<SID>') .. 'Format()', &formatexpr)
+  new | only
+  call setline(1, range(1, 40))
+  let g:FormatArgs = []
+  normal! 2GVjgq
+  call assert_equal([2, 2], g:FormatArgs)
+  bw!
+  set formatexpr=<SID>Format()
+  call assert_equal(expand('<SID>') .. 'Format()', &formatexpr)
+  new | only
+  call setline(1, range(1, 40))
+  let g:FormatArgs = []
+  normal! 4GVjgq
+  call assert_equal([4, 2], g:FormatArgs)
+  bw!
+  let &formatexpr = 's:Format()'
+  new | only
+  call setline(1, range(1, 40))
+  let g:FormatArgs = []
+  normal! 6GVjgq
+  call assert_equal([6, 2], g:FormatArgs)
+  bw!
+  let &formatexpr = '<SID>Format()'
+  new | only
+  call setline(1, range(1, 40))
+  let g:FormatArgs = []
+  normal! 8GVjgq
+  call assert_equal([8, 2], g:FormatArgs)
+  setlocal formatexpr=
+  delfunc s:Format
+  bw!
+endfunc
+
 " basic test for formatprg
 func Test_normal06_formatprg()
   " only test on non windows platform