vim-patch:8.2.2854: custom statusline cannot contain % items (#14558)

Problem:    Custom statusline cannot contain % items.
Solution:   Add "%{% expr %}". (closes vim/vim#8190)
https://github.com/vim/vim/commit/30e3de21fc36153c5f7c9cf9db90bcc60dd67fb9

4 files changed, 94 insertions, 3 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 2527a91cc8..4a6ae0245b 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5923,6 +5923,18 @@ A jump table for the options with a short description can be found at |Q_op|.
 	      Note that there is no '%' before the closing '}'.  The
 	      expression cannot contain a '}' character, call a function to
 	      work around that.  See |stl-%{| below.
+	{% -  This is almost same as { except the result of the expression is
+	      re-evaluated as a statusline format string.  Thus if the
+	      return value of expr contains % items they will get expanded.
+	      The expression can contain the } character, the end of
+	      expression is denoted by %}.
+	      The For example: >
+		func! Stl_filename() abort
+		    return "%t"
+		endfunc
+<	        `stl=%{Stl_filename()}`   results in `"%t"`
+	        `stl=%{%Stl_filename()%}` results in `"Name of current file"`
+	} -   End of `{%` expression
 	( -   Start of item group.  Can be used for setting the width and
 	      alignment of a section.  Must be followed by %) somewhere.
 	) -   End of item group.  No width fields allowed.
diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 5e700dea8a..6a50264e0f 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -85,6 +85,9 @@
 # include "buffer.c.generated.h"
 #endif
 
+// Determines how deeply nested %{} blocks will be evaluated in statusline.
+#define MAX_STL_EVAL_DEPTH 100
+
 static char *msg_loclist = N_("[Location List]");
 static char *msg_qflist = N_("[Quickfix List]");
 static char *e_auabort = N_("E855: Autocommands caused command to abort");
@@ -3572,6 +3575,7 @@ int build_stl_str_hl(
   }
 
   int groupdepth = 0;
+  int evaldepth  = 0;
 
   int curitem = 0;
   bool prevchar_isflag = true;
@@ -3909,6 +3913,13 @@ int build_stl_str_hl(
       continue;
     }
 
+    // Denotes end of expanded %{} block
+    if (*fmt_p == '}' && evaldepth > 0) {
+        fmt_p++;
+        evaldepth--;
+        continue;
+    }
+
     // An invalid item was specified.
     // Continue processing on the next character of the format string.
     if (vim_strchr(STL_ALL, *fmt_p) == NULL) {
@@ -3950,18 +3961,30 @@ int build_stl_str_hl(
     }
     case STL_VIM_EXPR:     // '{'
     {
+      char_u *block_start = fmt_p - 1;
+      int reevaluate = (*fmt_p == '%');
       itemisflag = true;
 
+      if (reevaluate) {
+        fmt_p++;
+      }
+
       // Attempt to copy the expression to evaluate into
       // the output buffer as a null-terminated string.
       char_u *t = out_p;
-      while (*fmt_p != '}' && *fmt_p != NUL && out_p < out_end_p)
+      while ((*fmt_p != '}' || (reevaluate && fmt_p[-1] != '%'))
+             && *fmt_p != NUL && out_p < out_end_p) {
         *out_p++ = *fmt_p++;
+      }
       if (*fmt_p != '}') {          // missing '}' or out of space
         break;
       }
       fmt_p++;
-      *out_p = 0;
+      if (reevaluate) {
+        out_p[-1] = 0;  // remove the % at the end of %{% expr %}
+      } else {
+        *out_p = 0;
+      }
 
       // Move our position in the output buffer
       // to the beginning of the expression
@@ -4007,6 +4030,40 @@ int build_stl_str_hl(
           itemisflag = false;
         }
       }
+
+
+      // If the output of the expression needs to be evaluated
+      // replace the %{} block with the result of evaluation
+      if (reevaluate && str != NULL && *str != 0
+          && strchr((const char *)str, '%') != NULL
+          && evaldepth < MAX_STL_EVAL_DEPTH) {
+        size_t parsed_usefmt = (size_t)(block_start - usefmt);
+        size_t str_length = strlen((const char *)str);
+        size_t fmt_length = strlen((const char *)fmt_p);
+        size_t new_fmt_len = parsed_usefmt
+          + str_length + fmt_length + 3;
+        char_u *new_fmt = (char_u *)xmalloc(new_fmt_len * sizeof(char_u));
+        char_u *new_fmt_p = new_fmt;
+
+        new_fmt_p = (char_u *)memcpy(new_fmt_p, usefmt, parsed_usefmt)
+          + parsed_usefmt;
+        new_fmt_p = (char_u *)memcpy(new_fmt_p , str, str_length)
+          + str_length;
+        new_fmt_p = (char_u *)memcpy(new_fmt_p, "%}", 2) + 2;
+        new_fmt_p = (char_u *)memcpy(new_fmt_p , fmt_p, fmt_length)
+          + fmt_length;
+        *new_fmt_p = 0;
+        new_fmt_p = NULL;
+
+        if (usefmt != fmt) {
+          xfree(usefmt);
+        }
+        XFREE_CLEAR(str);
+        usefmt = new_fmt;
+        fmt_p = usefmt + parsed_usefmt;
+        evaldepth++;
+        continue;
+      }
       break;
     }
 
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 6f28f37d2b..ad481af7fa 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -3641,9 +3641,11 @@ char_u *check_stl_option(char_u *s)
       return illegal_char(errbuf, sizeof(errbuf), *s);
     }
     if (*s == '{') {
+      int reevaluate = (*s == '%');
       s++;
-      while (*s != '}' && *s)
+      while ((*s != '}' || (reevaluate && s[-1] != '%')) && *s) {
         s++;
+      }
       if (*s != '}') {
         return (char_u *)N_("E540: Unclosed expression sequence");
       }
diff --git a/src/nvim/testdir/test_statusline.vim b/src/nvim/testdir/test_statusline.vim
index f5b6446108..a3e4dcdd25 100644
--- a/src/nvim/testdir/test_statusline.vim
+++ b/src/nvim/testdir/test_statusline.vim
@@ -241,6 +241,26 @@ func Test_statusline()
   call assert_match('^vimLineComment\s*$', s:get_statusline())
   syntax off
 
+  "%{%expr%}: evaluates enxpressions present in result of expr
+  func! Inner_eval()
+    return '%n some other text'
+  endfunc
+  func! Outer_eval()
+    return 'some text %{%Inner_eval()%}'
+  endfunc
+  set statusline=%{%Outer_eval()%}
+  call assert_match('^some text ' . bufnr() . ' some other text\s*$', s:get_statusline())
+  delfunc Inner_eval
+  delfunc Outer_eval
+
+  "%{%expr%}: Doesn't get stuck in recursion
+  func! Recurse_eval()
+    return '%{%Recurse_eval()%}'
+  endfunc
+  set statusline=%{%Recurse_eval()%}
+  call assert_match('^%{%Recurse_eval()%}\s*$', s:get_statusline())
+  delfunc Recurse_eval
+
   "%(: Start of item group.
   set statusline=ab%(cd%q%)de
   call assert_match('^abde\s*$', s:get_statusline())