vim-patch:8.2.4726: cannot use expand() to get the script name

Problem:    Cannot use expand() to get the script name.
Solution:   Support expand('<script>'). (closes vim/vim#10121)
6013d0045d

Use `.sn_name` instead of `->sn_name` as v8.2.0154 hasn't been ported.
Cherry-pick builtin.txt expand() doc from latest Vim.

src/nvim/ex_docmd.c

@@ -94,6 +94,12 @@ static char e_ambiguous_use_of_user_defined_command[]
   = N_("E464: Ambiguous use of user-defined command");
 static char e_not_an_editor_command[]
   = N_("E492: Not an editor command");
+static char e_no_source_file_name_to_substitute_for_sfile[]
+  = N_("E498: no :source file name to substitute for \"<sfile>\"");
+static char e_no_call_stack_to_substitute_for_stack[]
+  = N_("E489: no call stack to substitute for \"<stack>\"");
+static char e_no_script_file_name_to_substitute_for_script[]
+  = N_("E1274: No script file name to substitute for \"<script>\"");
 
 static int quitmore = 0;
 static bool ex_pressedreturn = false;
@@ -6564,6 +6570,7 @@ enum {
   SPEC_SFILE,
   SPEC_SLNUM,
   SPEC_STACK,
+  SPEC_SCRIPT,
   SPEC_AFILE,
   SPEC_ABUF,
   SPEC_AMATCH,
@@ -6588,6 +6595,7 @@ ssize_t find_cmdline_var(const char_u *src, size_t *usedlen)
     [SPEC_SFILE] = "<sfile>",           // ":so" file name
     [SPEC_SLNUM] = "<slnum>",           // ":so" file line number
     [SPEC_STACK] = "<stack>",           // call stack
+    [SPEC_SCRIPT] = "<script>",         // script file name
     [SPEC_AFILE] = "<afile>",           // autocommand file name
     [SPEC_ABUF] = "<abuf>",             // autocommand buffer number
     [SPEC_AMATCH] = "<amatch>",         // autocommand match name
@@ -6801,12 +6809,25 @@ char_u *eval_vars(char_u *src, char_u *srcstart, size_t *usedlen, linenr_T *lnum
       break;
 
     case SPEC_SFILE:            // file name for ":so" command
-    case SPEC_STACK:            // call stack
-      result = estack_sfile(spec_idx == SPEC_SFILE ? ESTACK_SFILE : ESTACK_STACK);
+      result = estack_sfile(ESTACK_SFILE);
       if (result == NULL) {
-        *errormsg = spec_idx == SPEC_SFILE
-          ? _("E498: no :source file name to substitute for \"<sfile>\"")
-          : _("E489: no call stack to substitute for \"<stack>\"");
+        *errormsg = _(e_no_source_file_name_to_substitute_for_sfile);
+        return NULL;
+      }
+      resultbuf = result;  // remember allocated string
+      break;
+    case SPEC_STACK:            // call stack
+      result = estack_sfile(ESTACK_STACK);
+      if (result == NULL) {
+        *errormsg = _(e_no_call_stack_to_substitute_for_stack);
+        return NULL;
+      }
+      resultbuf = result;  // remember allocated string
+      break;
+    case SPEC_SCRIPT:           // script file name
+      result = estack_sfile(ESTACK_SCRIPT);
+      if (result == NULL) {
+        *errormsg = _(e_no_script_file_name_to_substitute_for_script);
         return NULL;
       }
       resultbuf = result;  // remember allocated string

src/nvim/runtime.c

@@ -100,7 +100,8 @@ void estack_pop(void)
 }
 
 /// Get the current value for <sfile> in allocated memory.
-/// @param which  ESTACK_SFILE for <sfile> and ESTACK_STACK for <stack>.
+/// @param which  ESTACK_SFILE for <sfile>, ESTACK_STACK for <stack> or
+///               ESTACK_SCRIPT for <script>.
 char *estack_sfile(estack_arg_T which)
 {
   estack_T *entry = ((estack_T *)exestack.ga_data) + exestack.ga_len - 1;
@@ -111,6 +112,27 @@ char *estack_sfile(estack_arg_T which)
     return xstrdup(entry->es_name);
   }
 
+  // If evaluated in a function return the path of the script where the
+  // function is defined, at script level the current script path is returned
+  // instead.
+  if (which == ESTACK_SCRIPT) {
+    if (entry->es_type == ETYPE_UFUNC) {
+      sctx_T *def_ctx = &entry->es_info.ufunc->uf_script_ctx;
+      if (def_ctx->sc_sid > 0) {
+        return xstrdup((char *)(SCRIPT_ITEM(def_ctx->sc_sid).sn_name));
+      }
+    } else if (exestack.ga_len > 0) {
+      // Walk the stack backwards, starting from the current frame.
+      for (int idx = exestack.ga_len - 1; idx; idx--) {
+        entry = ((estack_T *)exestack.ga_data) + idx;
+        if (entry->es_type == ETYPE_SCRIPT) {
+          return xstrdup(entry->es_name);
+        }
+      }
+    }
+    return NULL;
+  }
+
   // Give information about each stack entry up to the root.
   // For a function we compose the call stack, as it was done in the past:
   //   "function One[123]..Two[456]..Three"

src/nvim/runtime.h

@@ -47,6 +47,7 @@ typedef enum {
   ESTACK_NONE,
   ESTACK_SFILE,
   ESTACK_STACK,
+  ESTACK_SCRIPT,
 } estack_arg_T;
 
 typedef struct scriptitem_S {

src/nvim/testdir/test_expand.vim

@@ -147,4 +147,54 @@ func Test_expandcmd_shell_nonomatch()
   call assert_equal('$*', expandcmd('$*'))
 endfunc
 
+func Test_expand_script_source()
+  let lines0 =<< trim [SCRIPT]
+    let g:script_level[0] = expand('<script>:t')
+    so Xscript1
+    func F0()
+      let g:func_level[0] = expand('<script>:t')
+    endfunc
+  [SCRIPT]
+
+  let lines1 =<< trim [SCRIPT]
+    let g:script_level[1] = expand('<script>:t')
+    so Xscript2
+    func F1()
+      let g:func_level[1] = expand('<script>:t')
+    endfunc
+  [SCRIPT]
+
+  let lines2 =<< trim [SCRIPT]
+    let g:script_level[2] = expand('<script>:t')
+    func F2()
+      let g:func_level[2] = expand('<script>:t')
+    endfunc
+  [SCRIPT]
+
+  call writefile(lines0, 'Xscript0')
+  call writefile(lines1, 'Xscript1')
+  call writefile(lines2, 'Xscript2')
+
+  " Check the expansion of <script> at script and function level.
+  let g:script_level = ['', '', '']
+  let g:func_level = ['', '', '']
+
+  so Xscript0
+  call F0()
+  call F1()
+  call F2()
+
+  call assert_equal(['Xscript0', 'Xscript1', 'Xscript2'], g:script_level)
+  call assert_equal(['Xscript0', 'Xscript1', 'Xscript2'], g:func_level)
+
+  unlet g:script_level g:func_level
+  delfunc F0
+  delfunc F1
+  delfunc F2
+
+  call delete('Xscript0')
+  call delete('Xscript1')
+  call delete('Xscript2')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab