Update wrt switch from pkger to custom ZIP pkging (#889)

Signed-off-by: Matej Vasek <mvasek@redhat.com>

docs/DEVELOPMENT.md

@@ -6,8 +6,6 @@ This document details how to get started contributing to the project.  This incl
 
 To build the core project, run `make` from the repository root.  This will result in a `func` binary being generated.  Run `make help` for additional targets and `./func help` for usage-centric documentation.
 
-Building currently requires that `pkger` be available in your `$PATH`.  This can be installed with `go get github.com/markbates/pkger/cmd/pkger`.  See [Templates](#templates) below for more information on this dependency.
-
 To remove built artifacts, use `make clean`.
 
 ## Testing

hack/verify-codegen.sh

@@ -29,17 +29,17 @@ cleanup() {
 trap "cleanup" EXIT SIGINT
 
 # Save working tree state
-cp -aR "${REPO_ROOT_DIR}/go.sum" "${REPO_ROOT_DIR}/pkged.go" "${REPO_ROOT_DIR}/vendor" "${TMP_DIFFROOT}"
+cp -aR "${REPO_ROOT_DIR}/go.sum" "${REPO_ROOT_DIR}/zz_filesystem_generated.go" "${REPO_ROOT_DIR}/vendor" "${TMP_DIFFROOT}"
 
 "${REPO_ROOT_DIR}/hack/update-codegen.sh"
 echo "Diffing ${REPO_ROOT_DIR} against freshly generated codegen"
 ret=0
 diff -Nupr --no-dereference "${REPO_ROOT_DIR}/go.sum" "${TMP_DIFFROOT}/go.sum" || ret=1
-diff -Nupr --no-dereference "${REPO_ROOT_DIR}/pkged.go" "${TMP_DIFFROOT}/pkged.go" || ret=1
+diff -Nupr --no-dereference "${REPO_ROOT_DIR}/zz_filesystem_generated.go" "${TMP_DIFFROOT}/zz_filesystem_generated.go" || ret=1
 diff -Nupr --no-dereference "${REPO_ROOT_DIR}/vendor" "${TMP_DIFFROOT}/vendor" || ret=1
 
 # Restore working tree state
-rm -fr "${REPO_ROOT_DIR}/go.sum" "${REPO_ROOT_DIR}/pkged.go" "${REPO_ROOT_DIR}/vendor"
+rm -fr "${REPO_ROOT_DIR}/go.sum" "${REPO_ROOT_DIR}/zz_filesystem_generated.go" "${REPO_ROOT_DIR}/vendor"
 cp -aR "${TMP_DIFFROOT}"/* "${REPO_ROOT_DIR}"
 
 if [[ $ret -eq 0 ]]

templates/README.md

@@ -2,23 +2,23 @@
 
 ## Packaging
 
-When updates are made to these templates, they must be packaged (serialized as
-a Go struture) by running `make`, and checking in the resultant `pkged.go` file.
+When updates are made to these templates, they must be packaged (serialized as a Go byte array)
+by running `make zz_filesystem_generated.go`, and checking in the resultant `zz_filesystem_generated.go` file.
 
 ## How it works
 
-running `make` in turn installs the `pkger` binary, which can be installed via:
-`go get github.com/markbates/pkger/cmd/pkger`
-Make then invokes `pkger` before `go build`.
-
-The resulting `pkged.go` file includes the contents of the templates directory,
-encoded as a Go strucutres which is then makde available in code using an API
-similar to the standard library's `os` package.
+The `./generate/templates` directory contains Go program that generates `zz_filesystem_generated.go`.
+The file defines byte array variable named `templatesZip`.
+The variable contains ZIP representation of the templates directory.
+The byte array variable is then used to instantiate exported global variable `function.EmbeddedTemplatesFS`,
+which implements standard Go interfaces `fs.ReadDirFS` and `fs.StatFS`.
 
 ## Rationale
 
 Until such time as embedding static assets in binaries is included in the
 base `go build` functionality (see https://github.com/golang/go/issues/35950)
-a third-party tool is required and pkger provides an API very similar  
-to the `os` package.
+we need to use our custom serialization script (`./generate/templates/main.go`).
 
+Native Go embedding introduced in Go 1.16 could be used for executable binary,
+however it cannot be used for library.
+For a library we need to generate a Go source code containing the templates.