vim-patch:8.1.1354: getting a list of text lines is clumsy

Problem:    Getting a list of text lines is clumsy.
Solution:   Add the =<< assignment. (Yegappan Lakshmanan, closes vim/vim#4386)
f5842c5a53

runtime/doc/eval.txt

@@ -9779,6 +9779,44 @@ This does NOT work: >
 			Like above, but append/add/subtract the value for each
 			|List| item.
 
+					*:let=<<* *:let-heredoc* *E990* *E991*
+:let {var-name} =<< [trim] {marker}
+text...
+text...
+{marker}
+			Set internal variable {var-name} to a List containing
+			the lines of text bounded by the string {marker}.
+			{marker} must not contain white space.
+			The last line should end only with the {marker} string
+			without any other character.  Watch out for white
+			space after {marker}!
+			If {marker} is not supplied, then "." is used as the
+			default marker.
+
+			Any white space characters in the lines of text are
+			preserved.  If "trim" is specified before {marker},
+			then all the leading indentation exactly matching the
+			leading indentation before `let` is stripped from the
+			input lines and the line containing {marker}.  Note
+			that the difference between space and tab matters
+			here.
+
+			If {var-name} didn't exist yet, it is created.
+			Cannot be followed by another command, but can be
+			followed by a comment.
+
+			Examples: >
+				let var1 =<< END
+			Sample text 1
+			    Sample text 2
+			Sample text 3
+			END
+
+				let data =<< trim DATA
+				1 2 3 4
+				5 6 7 8
+				DATA
+<
 								*E121*
 :let {var-name}	..	List the value of variable {var-name}.  Multiple
 			variable names may be given.  Special names recognized

src/nvim/eval.c

@@ -1504,6 +1504,87 @@ void ex_const(exarg_T *eap)
   ex_let_const(eap, true);
 }
 
+// Get a list of lines from a HERE document. The here document is a list of
+// lines surrounded by a marker.
+//     cmd << {marker}
+//       {line1}
+//       {line2}
+//       ....
+//     {marker}
+//
+// The {marker} is a string. If the optional 'trim' word is supplied before the
+// marker, then the leading indentation before the lines (matching the
+// indentation in the 'cmd' line) is stripped.
+// Returns a List with {lines} or NULL.
+static list_T *
+heredoc_get(exarg_T *eap, char_u *cmd)
+{
+  char_u *marker;
+  char_u *p;
+  int indent_len = 0;
+
+  if (eap->getline == NULL) {
+    EMSG(_("E991: cannot use =<< here"));
+    return NULL;
+  }
+
+  // Check for the optional 'trim' word before the marker
+  cmd = skipwhite(cmd);
+  if (STRNCMP(cmd, "trim", 4) == 0
+      && (cmd[4] == NUL || ascii_iswhite(cmd[4]))) {
+    cmd = skipwhite(cmd + 4);
+
+    // Trim the indentation from all the lines in the here document
+    // The amount of indentation trimmed is the same as the indentation of
+    // the :let command line.
+    p = *eap->cmdlinep;
+    while (ascii_iswhite(*p)) {
+      p++;
+      indent_len++;
+    }
+  }
+
+  // The marker is the next word.  Default marker is "."
+  if (*cmd != NUL && *cmd != '"') {
+    marker = skipwhite(cmd);
+    p = skiptowhite(marker);
+    if (*skipwhite(p) != NUL && *skipwhite(p) != '"') {
+      EMSG(_(e_trailing));
+      return NULL;
+    }
+    *p = NUL;
+  } else {
+    marker = (char_u *)".";
+  }
+
+  list_T *l = tv_list_alloc(0);
+  for (;;) {
+    int i = 0;
+
+    char_u *theline = eap->getline(NUL, eap->cookie, 0);
+    if (theline != NULL && indent_len > 0) {
+      // trim the indent matching the first line
+      if (STRNCMP(theline, *eap->cmdlinep, indent_len) == 0) {
+        i = indent_len;
+      }
+    }
+
+    if (theline == NULL) {
+      EMSG2(_("E990: Missing end marker '%s'"), marker);
+      break;
+    }
+    if (STRCMP(marker, theline + i) == 0) {
+      xfree(theline);
+      break;
+    }
+
+    tv_list_append_string(l, (char *)(theline + i), -1);
+    xfree(theline);
+  }
+
+  return l;
+}
+
 // ":let" list all variable values
 // ":let var1 var2" list variable values
 // ":let var = expr" assignment command.
@@ -1560,6 +1641,17 @@ static void ex_let_const(exarg_T *eap, const bool is_const)
       list_vim_vars(&first);
     }
     eap->nextcmd = check_nextcmd(arg);
+  } else if (expr[0] == '=' && expr[1] == '<' && expr[2] == '<') {
+    // HERE document
+    list_T *l = heredoc_get(eap, expr + 3);
+    if (l != NULL) {
+      tv_list_set_ret(&rettv, l);
+      op[0] = '=';
+      op[1] = NUL;
+      (void)ex_let_vars(eap->arg, &rettv, false, semicolon, var_count,
+                        is_const, op);
+      tv_clear(&rettv);
+    }
   } else {
     op[0] = '=';
     op[1] = NUL;

src/nvim/testdir/test_let.vim

@@ -140,3 +140,58 @@ func Test_let_varg_fail()
   call assert_fails('call s:set_varg7(1)', 'E742:')
   call s:set_varg8([0])
 endfunction
+
+
+" Test for the setting a variable using the heredoc syntax
+func Test_let_heredoc()
+  let var1 =<< END
+Some sample text
+	Text with indent
+  !@#$%^&*()-+_={}|[]\~`:";'<>?,./
+END
+
+  call assert_equal(["Some sample text", "\tText with indent", "  !@#$%^&*()-+_={}|[]\\~`:\";'<>?,./"], var1)
+
+  let var2 =<<
+Editor
+.
+  call assert_equal(['Editor'], var2)
+
+  let var3 =<<END
+END
+  call assert_equal([], var3)
+
+  let var3 =<<END
+vim
+
+end
+  END
+END 
+END
+  call assert_equal(['vim', '', 'end', '  END', 'END '], var3)
+
+        let var1 =<< trim END
+        Line1
+          Line2
+        	Line3
+         END
+        END
+  call assert_equal(['Line1', '  Line2', "\tLine3", ' END'], var1)
+
+  let var1 =<< trim
+    Line1
+  .
+  call assert_equal(['  Line1'], var1)
+
+  call assert_fails('let v =<< marker', 'E991:')
+  call assert_fails('call WrongSyntax()', 'E488:')
+  call assert_fails('call MissingEnd()', 'E990:')
+endfunc
+
+func WrongSyntax()
+  let fail =<< that there
+endfunc
+
+func MissingEnd()
+  let fail =<< END
+endfunc