Only unquote --variable when it appears quoted

The change to unquote values in the --variable output broke users that
had shell special characters in the variable. Instead, only unquote if
the value starts with " or '. A larger fix to do a full unquote, split
and escaping like --cflags/--libs is possible, but that might break the
old semantics even further.

Add a new function, parse_package_variable(), to handle that logic.

https://bugs.freedesktop.org/show_bug.cgi?id=93284

parse.c

@@ -1145,3 +1145,39 @@ parse_package_file (const char *key, const char *path,
   
   return pkg;
 }
+
+/* Parse a package variable. When the value appears to be quoted,
+ * unquote it so it can be more easily used in a shell. Otherwise,
+ * return the raw value.
+ */
+char *
+parse_package_variable (Package *pkg, const char *variable)
+{
+  char *value;
+  char *unquoted;
+  GError *error = NULL;
+
+  value = package_get_var (pkg, variable);
+  if (!value)
+    return NULL;
+
+  if (*value != '"' && *value != '\'')
+    /* Not quoted, return raw value */
+    return value;
+
+  /* Maybe too naive, but assume a fully quoted variable */
+  unquoted = g_shell_unquote (value, &error);
+  if (unquoted)
+    {
+      g_free (value);
+      return unquoted;
+    }
+  else
+    {
+      /* Note the issue, but just return the raw value */
+      debug_spew ("Couldn't unquote value of \"%s\": %s\n",
+                  variable, error ? error->message : "unknown");
+      g_clear_error (&error);
+      return value;
+    }
+}

parse.h

@@ -29,6 +29,8 @@ Package *parse_package_file (const char *key, const char *path,
 
 GList   *parse_module_list (Package *pkg, const char *str, const char *path);
 
+char    *parse_package_variable (Package *pkg, const char *variable);
+
 #endif
 
 

pkg.c

@@ -1070,40 +1070,33 @@ package_get_var (Package *pkg,
 }
 
 char *
-packages_get_var (GList     *pkgs,
+packages_get_var (GList      *pkgs,
                   const char *varname)
 {
   GList *tmp;
   GString *str;
-  char *retval;
-  
-  str = g_string_new ("");
-  
+
+  str = g_string_new (NULL);
+
   tmp = pkgs;
   while (tmp != NULL)
     {
       Package *pkg = tmp->data;
       char *var;
 
-      var = package_get_var (pkg, varname);
-      
+      var = parse_package_variable (pkg, varname);
       if (var)
         {
+          if (str->len > 0)
+            g_string_append_c (str, ' ');
           g_string_append (str, var);
-          g_string_append_c (str, ' ');                
           g_free (var);
         }
 
       tmp = g_list_next (tmp);
     }
 
-  /* chop last space */
-  if (str->len > 0)
-      str->str[str->len - 1] = '\0';
-  retval = str->str;
-  g_string_free (str, FALSE);
-
-  return retval;
+  return g_string_free (str, FALSE);
 }
 
 int