vim-patch:9.1.0312: heredocs are not supported for :commands

Problem:  heredocs are not supported for :commands
          (balki)
Solution: Add heredoc support
          (Yegappan Lakshmanan)

fixes: vim/vim#14491
closes: vim/vim#14528

https://github.com/vim/vim/commit/e74cad3321ce1dcefc1fc64f617511275b6cd930

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

3 files changed, 78 insertions, 18 deletions

diff --git a/src/nvim/charset.c b/src/nvim/charset.c
index 2e6f24b2d5..59932b2eb0 100644
--- a/src/nvim/charset.c
+++ b/src/nvim/charset.c
@@ -1045,13 +1045,27 @@ char *skiptowhite(const char *p)
   return (char *)p;
 }
 
+/// Skip over text until ' ' or '\t' or newline or NUL
+///
+/// @param[in]  p  Text to skip over.
+///
+/// @return Pointer to the next whitespace or newline or NUL character.
+char *skiptowhite_or_nl(const char *p)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE
+{
+  while (*p != ' ' && *p != '\t' && *p != NL && *p != NUL) {
+    p++;
+  }
+  return (char *)p;
+}
+
 /// skiptowhite_esc: Like skiptowhite(), but also skip escaped chars
 ///
 /// @param p
 ///
 /// @return Pointer to the next whitespace character.
 char *skiptowhite_esc(const char *p)
-  FUNC_ATTR_PURE
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE
 {
   while (*p != ' ' && *p != '\t' && *p != NUL) {
     if (((*p == '\\') || (*p == Ctrl_V)) && (*(p + 1) != NUL)) {
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 65e648b625..70ecb76deb 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -62,8 +62,8 @@ static const char e_double_semicolon_in_list_of_variables[]
 static const char *e_lock_unlock = N_("E940: Cannot lock or unlock variable %s");
 static const char e_setting_v_str_to_value_with_wrong_type[]
   = N_("E963: Setting v:%s to value with wrong type");
-static const char e_cannot_use_heredoc_here[]
-  = N_("E991: Cannot use =<< here");
+static const char e_missing_end_marker_str[] = N_("E990: Missing end marker '%s'");
+static const char e_cannot_use_heredoc_here[] = N_("E991: Cannot use =<< here");
 
 /// Evaluate one Vim expression {expr} in string "p" and append the
 /// resulting string to "gap".  "p" points to the opening "{".
@@ -180,7 +180,7 @@ list_T *heredoc_get(exarg_T *eap, char *cmd, bool script_get)
   char *text_indent = NULL;
   char dot[] = ".";
 
-  if (eap->ea_getline == NULL) {
+  if (eap->ea_getline == NULL && vim_strchr(cmd, '\n') == NULL) {
     emsg(_(e_cannot_use_heredoc_here));
     return NULL;
   }
@@ -216,11 +216,18 @@ list_T *heredoc_get(exarg_T *eap, char *cmd, bool script_get)
     break;
   }
 
+  const char comment_char = '"';
+  bool heredoc_in_string = false;
+  char *line_arg = NULL;
   // The marker is the next word.
-  if (*cmd != NUL && *cmd != '"') {
+  if (*cmd != NUL && *cmd != comment_char) {
     marker = skipwhite(cmd);
-    char *p = skiptowhite(marker);
-    if (*skipwhite(p) != NUL && *skipwhite(p) != '"') {
+    char *p = skiptowhite_or_nl(marker);
+    if (*p == NL) {
+      // heredoc in a string
+      line_arg = p + 1;
+      heredoc_in_string = true;
+    } else if (*skipwhite(p) != NUL && *skipwhite(p) != comment_char) {
       semsg(_(e_trailing_arg), p);
       return NULL;
     }
@@ -246,13 +253,34 @@ list_T *heredoc_get(exarg_T *eap, char *cmd, bool script_get)
     int mi = 0;
     int ti = 0;
 
-    xfree(theline);
-    theline = eap->ea_getline(NUL, eap->cookie, 0, false);
-    if (theline == NULL) {
-      if (!script_get) {
-        semsg(_("E990: Missing end marker '%s'"), marker);
+    if (heredoc_in_string) {
+      // heredoc in a string separated by newlines.  Get the next line
+      // from the string.
+
+      if (*line_arg == NUL) {
+        if (!script_get) {
+          semsg(_(e_missing_end_marker_str), marker);
+        }
+        break;
+      }
+
+      theline = line_arg;
+      char *next_line = vim_strchr(theline, '\n');
+      if (next_line == NULL) {
+        line_arg += strlen(line_arg);
+      } else {
+        *next_line = NUL;
+        line_arg = next_line + 1;
+      }
+    } else {
+      xfree(theline);
+      theline = eap->ea_getline(NUL, eap->cookie, 0, false);
+      if (theline == NULL) {
+        if (!script_get) {
+          semsg(_(e_missing_end_marker_str), marker);
+        }
+        break;
       }
-      break;
     }
 
     // with "trim": skip the indent matching the :let line to find the
@@ -298,13 +326,17 @@ list_T *heredoc_get(exarg_T *eap, char *cmd, bool script_get)
         eval_failed = true;
         continue;
       }
-      xfree(theline);
-      theline = str;
+      tv_list_append_allocated_string(l, str);
+    } else {
+      tv_list_append_string(l, str, -1);
     }
-
-    tv_list_append_string(l, str, -1);
   }
-  xfree(theline);
+  if (heredoc_in_string) {
+    // Next command follows the heredoc in the string.
+    eap->nextcmd = line_arg;
+  } else {
+    xfree(theline);
+  }
   xfree(text_indent);
 
   if (eval_failed) {
diff --git a/test/old/testdir/test_let.vim b/test/old/testdir/test_let.vim
index 655c177385..56b880f3b0 100644
--- a/test/old/testdir/test_let.vim
+++ b/test/old/testdir/test_let.vim
@@ -713,6 +713,20 @@ END
   LINES
   call CheckScriptFailure(lines, 'E15:')
 
+  " Test for using heredoc in a single string using execute()
+  call assert_equal(["['one', 'two']"],
+    \ execute("let x =<< trim END\n  one\n  two\nEND\necho x")->split("\n"))
+  call assert_equal(["['  one', '  two']"],
+    \ execute("let x =<< END\n  one\n  two\nEND\necho x")->split("\n"))
+  let cmd = 'execute("let x =<< END\n  one\n  two\necho x")'
+  call assert_fails(cmd, "E990: Missing end marker 'END'")
+  let cmd = 'execute("let x =<<\n  one\n  two\necho x")'
+  call assert_fails(cmd, "E990: Missing end marker ''")
+  let cmd = 'execute("let x =<< trim\n  one\n  two\necho x")'
+  call assert_fails(cmd, "E221: Marker cannot start with lower case letter")
+  let cmd = 'execute("let x =<< eval END\n  one\n  two{y}\nEND\necho x")'
+  call assert_fails(cmd, 'E121: Undefined variable: y')
+
   " skipped heredoc
   if 0
     let msg =<< trim eval END