Use a general approach to access custom/static/builtin assets (#24022)

The idea is to use a Layered Asset File-system (modules/assetfs/layered.go)

For example: when there are 2 layers: "custom", "builtin", when access
to asset "my/page.tmpl", the Layered Asset File-system will first try to
use "custom" assets, if not found, then use "builtin" assets.

This approach will hugely simplify a lot of code, make them testable.

Other changes:

* Simplify the AssetsHandlerFunc code
* Simplify the `gitea embedded` sub-command code

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

2 files changed, 16 insertions, 0 deletions

diff --git a/modules/setting/asset_dynamic.go b/modules/setting/asset_dynamic.go
new file mode 100644
index 0000000000..2eb2883373
--- /dev/null
+++ b/modules/setting/asset_dynamic.go
@@ -0,0 +1,8 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !bindata
+
+package setting
+
+const HasBuiltinBindata = false
diff --git a/modules/setting/asset_static.go b/modules/setting/asset_static.go
new file mode 100644
index 0000000000..889fca9342
--- /dev/null
+++ b/modules/setting/asset_static.go
@@ -0,0 +1,8 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build bindata
+
+package setting
+
+const HasBuiltinBindata = true