firstboot,sysinstall,hostnamed: always show FANCY_NAME=

This makes sure that whenever we want to show the OS name we can show
the fancy name. Thus this moves the escaping/validation of the fancy
name out of hostnamed into generic code, and then makes use of it in
sysinstall,firstboot,prompt-util.

src/basic/os-util.c

@@ -3,10 +3,12 @@
 #include <stdlib.h>
 
 #include "alloc-util.h"
+#include "ansi-color.h"
 #include "chase.h"
 #include "dirent-util.h"
 #include "env-file.h"
 #include "errno-util.h"
+#include "escape.h"
 #include "fd-util.h"
 #include "fs-util.h"
 #include "glyph-util.h"
@@ -512,3 +514,46 @@ const char* os_release_pretty_name(const char *pretty_name, const char *name) {
         return empty_to_null(pretty_name) ?:
                 empty_to_null(name) ?: "Linux";
 }
+
+char *unescape_fancy_name(char **fancy_name) {
+        assert(fancy_name);
+
+        /* Checks if the fancy name is valid, unescapes if it is, nullifies it if not */
+
+        _cleanup_free_ char *unescaped_fancy_name = NULL;
+
+        if (isempty(*fancy_name))
+                goto clear;
+
+        /* We undo one level of C escapes on this */
+        ssize_t n = cunescape(*fancy_name, /* flags= */ 0, &unescaped_fancy_name);
+        if (n < 0) {
+                log_debug_errno((int) n, "Failed to unescape FANCY_NAME= string, suppressing: %m");
+                goto clear;
+        }
+
+        if (!utf8_is_valid(unescaped_fancy_name)) {
+                log_debug("Unescaped FANCY_NAME= string is not valid UTF-8, suppressing.");
+                goto clear;
+        }
+
+        free_and_replace(*fancy_name, unescaped_fancy_name);
+        return *fancy_name;
+
+clear:
+        *fancy_name = mfree(*fancy_name);
+        return NULL;
+}
+
+bool use_fancy_name(const char *fancy_name) {
+
+        /* Decides whether to show the specified fancy name */
+
+        if (isempty(fancy_name))
+                return false;
+
+        if (!colors_enabled())
+                return false;
+
+        return emoji_enabled() || ascii_is_valid(fancy_name);
+}

src/basic/os-util.h

@@ -55,3 +55,6 @@ int load_os_release_pairs_with_prefix(const char *root, const char *prefix, char
 int os_release_support_ended(const char *support_end, bool quiet, usec_t *ret_eol);
 
 const char* os_release_pretty_name(const char *pretty_name, const char *name);
+
+bool use_fancy_name(const char *fancy_name);
+char *unescape_fancy_name(char **fancy_name);