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)

36a5b6867b

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>

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;
   }

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',
   },

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.

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"));