patch 8.2.1347: cannot easily get the script ID

Problem:    Cannot easily get the script ID.
Solution:   Support expand('<SID>').

runtime/doc/map.txt

@@ -1167,6 +1167,10 @@ When executing an autocommand or a user command, it will run in the context of
 the script it was defined in.  This makes it possible that the command calls a
 local function or uses a local mapping.
 
+In case the value is used in a context where <SID> cannot be correctly
+expanded, use the expand() function: >
+	let &includexpr = expand('<SID>') .. 'My_includeexpr()'
+
 Otherwise, using "<SID>" outside of a script context is an error.
 
 If you need to get the script number to use in a complicated script, you can

src/ex_docmd.c

@@ -8302,9 +8302,11 @@ find_cmdline_var(char_u *src, int *usedlen)
 #define SPEC_AMATCH (SPEC_ABUF + 1)
 		    "<sflnum>",		// script file line number
 #define SPEC_SFLNUM  (SPEC_AMATCH + 1)
+		    "<SID>",		// script ID: <SNR>123_
+#define SPEC_SID  (SPEC_SFLNUM + 1)
 #ifdef FEAT_CLIENTSERVER
 		    "<client>"
-# define SPEC_CLIENT (SPEC_SFLNUM + 1)
+# define SPEC_CLIENT (SPEC_SID + 1)
 #endif
     };
 
@@ -8581,6 +8583,16 @@ eval_vars(
 		break;
 #endif
 
+	case SPEC_SID:
+		if (current_sctx.sc_sid <= 0)
+		{
+		    *errormsg = _(e_usingsid);
+		    return NULL;
+		}
+		sprintf((char *)strbuf, "<SNR>%d_", current_sctx.sc_sid);
+		result = strbuf;
+		break;
+
 #ifdef FEAT_CLIENTSERVER
 	case SPEC_CLIENT:	// Source of last submitted input
 		sprintf((char *)strbuf, PRINTF_HEX_LONG_U,

src/testdir/test_expand_func.vim

@@ -1,5 +1,7 @@
 " Tests for expand()
 
+source shared.vim
+
 let s:sfile = expand('<sfile>')
 let s:slnum = str2nr(expand('<slnum>'))
 let s:sflnum = str2nr(expand('<sflnum>'))
@@ -18,20 +20,20 @@ endfunc
 
 " This test depends on the location in the test file, put it first.
 func Test_expand_sflnum()
-  call assert_equal(5, s:sflnum)
+  call assert_equal(7, s:sflnum)
-  call assert_equal(22, str2nr(expand('<sflnum>')))
+  call assert_equal(24, str2nr(expand('<sflnum>')))
 
   " Line-continuation
   call assert_equal(
-        \ 25,
+        \ 27,
         \ str2nr(expand('<sflnum>')))
 
   " Call in script-local function
-  call assert_equal(16, s:expand_sflnum())
+  call assert_equal(18, s:expand_sflnum())
 
   " Call in command
   command Flnum echo expand('<sflnum>')
-  call assert_equal(34, str2nr(trim(execute('Flnum'))))
+  call assert_equal(36, str2nr(trim(execute('Flnum'))))
   delcommand Flnum
 endfunc
 
@@ -60,7 +62,7 @@ func Test_expand_sfile_and_stack()
 endfunc
 
 func Test_expand_slnum()
-  call assert_equal(4, s:slnum)
+  call assert_equal(6, s:slnum)
   call assert_equal(2, str2nr(expand('<slnum>')))
 
   " Line-continuation
@@ -86,6 +88,17 @@ func Test_expand()
   quit
 endfunc
 
+func s:sid_test()
+  return 'works'
+endfunc
+
+func Test_expand_SID()
+  let sid = expand('<SID>')
+  execute 'let g:sid_result = ' .. sid .. 'sid_test()'
+  call assert_equal('works', g:sid_result)
+endfunc
+
+
 " Test for 'wildignore' with expand()
 func Test_expand_wildignore()
   set wildignore=*.vim

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1347,
 /**/
     1346,
 /**/