panel: implement extension and basename display for user-defined formats

The extension panel field used string_file_name as its display callback,
showing the full filename instead of just the extension. There was
already a TODO comment acknowledging this (// TODO: string_file_ext).

Add string_file_ext() which returns only the part after the last dot
for regular files, or an empty string for directories and extensionless
files.

Add string_file_basename() which returns the filename without its
extension (without the trailing dot), complementing the extension field.

Both fields are documented in the man page.

Example user_format: half basename | extension | size | mtime

Signed-off-by: Ilia Karpov <iakarpov@edu.hse.ru>
Signed-off-by: ki <karpovilia@gmail.com>

Author: karpovilia

doc/man/mc.1.in

@@ -798,6 +798,14 @@ specifier.  This are the available fields you may display:
 .B name
 displays the file name.
 .TP
+.B basename
+displays the file name without extension. For directories and files
+without an extension, this is identical to the full name.
+.TP
+.B extension
+displays the file extension (the part after the last dot).
+For directories and files without an extension, this field is empty.
+.TP
 .B size
 displays the file size.
 .TP

src/filemanager/panel.c

@@ -159,6 +159,8 @@ static const char *string_file_group (const file_entry_t *fe, int len);
 static const char *string_marked (const file_entry_t *fe, int len);
 static const char *string_space (const file_entry_t *fe, int len);
 static const char *string_dot (const file_entry_t *fe, int len);
+static const char *string_file_ext (const file_entry_t *fe, int len);
+static const char *string_file_basename (const file_entry_t *fe, int len);
 
 /*** file scope variables ************************************************************************/
 
@@ -178,9 +180,9 @@ static panel_field_t panel_fields[] = {
     { "extension", 12, TRUE, J_LEFT_FIT,
       // TRANSLATORS: one single character to represent 'extension' sort mode
       // TRANSLATORS: no need to translate 'sort', it's just a context prefix
-      N_ ("sort|e"), N_ ("E&xtension"), TRUE, FALSE,
-      string_file_name,  // TODO: string_file_ext
-      (GCompareFunc) sort_ext },
+      N_ ("sort|e"), N_ ("E&xtension"), TRUE, FALSE, string_file_ext, (GCompareFunc) sort_ext },
+    { "basename", 12, TRUE, J_LEFT_FIT, N_ ("sort|n"), N_ ("&Basename"), TRUE, FALSE,
+      string_file_basename, (GCompareFunc) sort_name },
     { "size", 7, FALSE, J_RIGHT,
       // TRANSLATORS: one single character to represent 'size' sort mode
       // TRANSLATORS: no need to translate 'sort', it's just a context prefix
@@ -355,6 +357,42 @@ string_file_name (const file_entry_t *fe, int len)
 
 /* --------------------------------------------------------------------------------------------- */
 
+static const char *
+string_file_ext (const file_entry_t *fe, MC_UNUSED int len)
+{
+    const char *ext = extension (fe->fname->str);
+
+    if (ext[0] == '\0' || S_ISDIR (fe->st.st_mode))
+        g_string_truncate (string_file_name_buffer, 0);
+    else
+        g_string_assign (string_file_name_buffer, ext);
+
+    return string_file_name_buffer->str;
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+static const char *
+string_file_basename (const file_entry_t *fe, MC_UNUSED int len)
+{
+    const char *ext = extension (fe->fname->str);
+
+    mc_g_string_copy (string_file_name_buffer, fe->fname);
+
+    /* Remove the extension (including the dot) from the name */
+    if (ext[0] != '\0' && !S_ISDIR (fe->st.st_mode))
+    {
+        size_t name_len = (size_t) (ext - fe->fname->str);
+
+        if (name_len > 0)
+            g_string_truncate (string_file_name_buffer, name_len - 1);
+    }
+
+    return string_file_name_buffer->str;
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
 static unsigned int
 ilog10 (dev_t n)
 {