builder-context: Write a gitignore file into the state-dir

Unless specified, state-dir is placed on the current path,
which is usually the source directory of the project.

Write a .gitignore file to make sure that both the state-dir
never gets checked out into git and that all the tooling
will ignore it and avoid indexing it.

Inpired by meson's gitignore file in the build directories.

Retro-actively discovered the same change in flatpak-build init [1]

[1]: flatpak/flatpak@a62f8cf

src/builder-context.c

@@ -37,6 +37,9 @@
 #include "builder-cache.h"
 #include "builder-utils.h"
 
+#define GIT_IGNORE_FILE \
+  "# This file is autogenerated by flatpak-builder.\n" \
+  "*\n"
 
 struct BuilderContext
 {
@@ -1193,6 +1196,41 @@ builder_context_get_sdk_config (BuilderContext *self)
   return self->sdk_config;
 }
 
+gboolean
+builder_context_create_state_dir (BuilderContext *self,
+                                  GError        **error)
+{
+  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
+
+  if (!g_file_make_directory_with_parents (self->state_dir, NULL, error))
+  {
+    if (g_error_matches (*error, G_IO_ERROR, G_IO_ERROR_EXISTS))
+      {
+        g_clear_error (error);
+        return TRUE;
+      }
+
+    flatpak_fail (error, "Could not create state-dir");
+    return FALSE;
+  }
+
+  // Only create the gitignore file if we were the ones to create the state-dir
+  // Assume that if the state-dir exists already, there's either already a file
+  // created before or it was deliberately modified or deleted
+  g_autoptr (GFile) gitignore_file = g_file_get_child (self->state_dir, ".gitignore");
+  if (!g_file_replace_contents (gitignore_file,
+                                GIT_IGNORE_FILE, sizeof (GIT_IGNORE_FILE),
+                                NULL, FALSE,
+                                G_FILE_CREATE_REPLACE_DESTINATION,
+                                NULL, NULL, error))
+  {
+    flatpak_fail (error, "Could not create .gitignore file inside state-dir");
+    return FALSE;
+  }
+
+  return TRUE;
+}
+
 BuilderContext *
 builder_context_new (GFile *run_dir,
                      GFile *app_dir,

src/builder-context.h

@@ -182,6 +182,9 @@ const char *    builder_context_get_opt_mirror_screenshots_url (BuilderContext *
 
 BuilderSdkConfig * builder_context_get_sdk_config (BuilderContext *self);
 
+gboolean        builder_context_create_state_dir (BuilderContext *self,
+                                                  GError        **error);
+
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (BuilderContext, g_object_unref)
 
 G_END_DECLS

src/builder-main.c

@@ -533,6 +533,12 @@ main (int    argc,
 
   git_init_email ();
 
+  if (!builder_context_create_state_dir (build_context, &error))
+  {
+    g_printerr ("Can't create state directory: %s\n", error->message);
+    return 1;
+  }
+
   if (opt_sources_dirs)
     {
       g_autoptr(GPtrArray) sources_dirs = NULL;