vim-patch:8.2.4594: need to write script to a file to be able to source them

Problem:    Need to write script to a file to be able to source them.
Solution:   Make ":source" use lines from the current buffer. (Yegappan
            Lakshmanan et al., closes vim/vim#9967)

https://github.com/vim/vim/commit/36a5b6867bb6c0bd69c8da7d788000ab8a0b0ab0

Most code and test changes are reverted or modified again in patch
8.2.4603, so only port parts that are untouched in patch 8.2.4603.

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

6 files changed, 48 insertions, 16 deletions

diff --git a/runtime/doc/repeat.txt b/runtime/doc/repeat.txt
index e65caa72ed..4c95066998 100644
--- a/runtime/doc/repeat.txt
+++ b/runtime/doc/repeat.txt
@@ -192,14 +192,19 @@ Using Vim scripts					*using-scripts*
 For writing a Vim script, see chapter 41 of the user manual |usr_41.txt|.
 
 					*:so* *:source* *load-vim-script*
-:[range]so[urce] [file]	Runs |Ex-commands| or Lua code (".lua" files) from
-			[file].
-			If no [file], the current buffer is used and treated
-			as Lua code if 'filetype' is "lua" or its filename
-			ends with ".lua".
+:so[urce] {file}	Runs |Ex-commands| or Lua code (".lua" files) from
+			{file}.
 			Triggers the |SourcePre| autocommand.
+
+:[range]so[urce]	Read Ex commands or Lua code from the [range] of lines
+			in the current buffer.  The buffer is treated as Lua
+			code if 'filetype' is "lua" or its filename ends with
+			".lua".  When sourcing commands or Lua code from the
+			current buffer, the same script-ID |<SID>| is used
+			even if the buffer is sourced multiple times.
+
 							*:source!*
-:[range]so[urce]! {file}
+:so[urce]! {file}
 			Runs |Normal-mode| commands from {file}. When used
 			after |:global|, |:argdo|, |:windo|, |:bufdo|, in
 			a loop or when another command follows the display
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 2b6fefbf82..ee5dd25e93 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -759,7 +759,7 @@ void fill_evalarg_from_eap(evalarg_T *evalarg, exarg_T *eap, bool skip)
     return;
   }
 
-  if (getline_equal(eap->ea_getline, eap->cookie, getsourceline)) {
+  if (sourcing_a_script(eap)) {
     evalarg->eval_getline = eap->ea_getline;
     evalarg->eval_cookie = eap->cookie;
   }
diff --git a/src/nvim/ex_cmds.lua b/src/nvim/ex_cmds.lua
index d118c808d3..d68d5a9afa 100644
--- a/src/nvim/ex_cmds.lua
+++ b/src/nvim/ex_cmds.lua
@@ -2533,7 +2533,7 @@ M.cmds = {
   },
   {
     command = 'source',
-    flags = bit.bor(RANGE, DFLALL, WHOLEFOLD, BANG, FILE1, TRLBAR, SBOXOK, CMDWIN, LOCK_OK),
+    flags = bit.bor(RANGE, DFLALL, BANG, FILE1, TRLBAR, SBOXOK, CMDWIN, LOCK_OK),
     addr_type = 'ADDR_LINES',
     func = 'ex_source',
   },
diff --git a/src/nvim/garray.c b/src/nvim/garray.c
index a8d15a1fa8..b3dce90b11 100644
--- a/src/nvim/garray.c
+++ b/src/nvim/garray.c
@@ -198,12 +198,13 @@ void ga_concat(garray_T *gap, const char *restrict s)
 void ga_concat_len(garray_T *const gap, const char *restrict s, const size_t len)
   FUNC_ATTR_NONNULL_ALL
 {
-  if (len) {
-    ga_grow(gap, (int)len);
-    char *data = gap->ga_data;
-    memcpy(data + gap->ga_len, s, len);
-    gap->ga_len += (int)len;
+  if (len == 0) {
+    return;
   }
+  ga_grow(gap, (int)len);
+  char *data = gap->ga_data;
+  memcpy(data + gap->ga_len, s, len);
+  gap->ga_len += (int)len;
 }
 
 /// Append one byte to a growarray which contains bytes.
diff --git a/src/nvim/runtime.c b/src/nvim/runtime.c
index 861a44cc05..f02c8660f1 100644
--- a/src/nvim/runtime.c
+++ b/src/nvim/runtime.c
@@ -106,6 +106,7 @@ garray_T script_items = { 0, 0, sizeof(scriptitem_T *), 20, NULL };
 /// The names of packages that once were loaded are remembered.
 static garray_T ga_loaded = { 0, 0, sizeof(char *), 4, NULL };
 
+/// last used sequence number for sourcing scripts (current_sctx.sc_seq)
 static int last_current_SID_seq = 0;
 
 /// Initialize the execution stack.
@@ -1825,8 +1826,20 @@ freeall:
 
 static void cmd_source(char *fname, exarg_T *eap)
 {
+  if (*fname != NUL && eap != NULL && eap->addr_count > 0) {
+    // if a filename is specified to :source, then a range is not allowed
+    emsg(_(e_norange));
+    return;
+  }
+
   if (eap != NULL && *fname == NUL) {
-    cmd_source_buffer(eap, false);
+    if (eap->forceit) {
+      // a file name is needed to source normal mode commands
+      emsg(_(e_argreq));
+    } else {
+      // source ex commands from the current buffer
+      cmd_source_buffer(eap, false);
+    }
   } else if (eap != NULL && eap->forceit) {
     // ":source!": read Normal mode commands
     // Need to execute the commands directly.  This is required at least
@@ -2784,11 +2797,18 @@ retry:
   return NULL;
 }
 
+/// Returns true if sourcing a script either from a file or a buffer.
+/// Otherwise returns false.
+int sourcing_a_script(exarg_T *eap)
+{
+  return getline_equal(eap->ea_getline, eap->cookie, getsourceline);
+}
+
 /// ":scriptencoding": Set encoding conversion for a sourced script.
 /// Without the multi-byte feature it's simply ignored.
 void ex_scriptencoding(exarg_T *eap)
 {
-  if (!getline_equal(eap->ea_getline, eap->cookie, getsourceline)) {
+  if (!sourcing_a_script(eap)) {
     emsg(_("E167: :scriptencoding used outside of a sourced file"));
     return;
   }
@@ -2807,7 +2827,7 @@ void ex_scriptencoding(exarg_T *eap)
 /// ":finish": Mark a sourced file as finished.
 void ex_finish(exarg_T *eap)
 {
-  if (getline_equal(eap->ea_getline, eap->cookie, getsourceline)) {
+  if (sourcing_a_script(eap)) {
     do_finish(eap, false);
   } else {
     emsg(_("E168: :finish used outside of a sourced file"));
diff --git a/test/old/testdir/test_source.vim b/test/old/testdir/test_source.vim
index 01c08b183c..130d859224 100644
--- a/test/old/testdir/test_source.vim
+++ b/test/old/testdir/test_source.vim
@@ -92,6 +92,12 @@ func Test_source_error()
   call assert_fails('scriptencoding utf-8', 'E167:')
   call assert_fails('finish', 'E168:')
   " call assert_fails('scriptversion 2', 'E984:')
+  call assert_fails('source!', 'E471:')
+  new
+  call setline(1, ['', '', '', ''])
+  call assert_fails('1,3source Xscript.vim', 'E481:')
+  call assert_fails('1,3source! Xscript.vim', 'E481:')
+  bw!
 endfunc
 
 " Test for sourcing a script recursively