Fix the Bazel build.

Uses `gazelle` to generate the needed changes to import new
dependencies. This is following
https://www.tweag.io/blog/2021-09-08-rules_go-gazelle/ tutorial. At some
later point, we might want to update the go toolchain, gazelle version,
bazel version, etc.

Also added comments so that future changes to dependencies / code that
gets builds would result in easy to (auto-)generate `BUILD` file
changes.

Author: mihaimaruseac

BUILD

@@ -1,6 +1,35 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_binary")
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("@bazel_gazelle//:def.bzl", "gazelle")
 
+# Run `bazel run //:gazelle` each time you add a new directory.
+# As a result, `BUILD` files will be generated for you within that directory.
+# gazelle:prefix github.com/slsa-framework/example-package
+gazelle(name = "gazelle")
+
+# Run `bazel run //:gazelle-update-repos` each time `go.mod` changes (e.g., you
+# add a new dependency). This would result in Bazel workspace dependencies also
+# being brought up to date.
+gazelle(
+    name = "gazelle-update-repos",
+    args = [
+        "-from_file=go.mod",
+        "-to_macro=deps.bzl%go_dependencies",
+        "-prune",
+    ],
+    command = "update-repos",
+)
+
+# Existing rules (you can write your own or use the ones generated by `gazelle`).
 go_binary(
     name = "hello",
+    embed = [":example-package_lib"],
+    visibility = ["//visibility:public"],
+)
+
+go_library(
+    name = "example-package_lib",
     srcs = ["main.go"],
+    importpath = "github.com/slsa-framework/example-package",
+    visibility = ["//visibility:private"],
+    deps = ["@com_github_pborman_uuid//:uuid"],
 )

WORKSPACE

@@ -1,3 +1,5 @@
+workspace(name = "com_github_slsa_framework_example_package")
+
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 http_archive(
@@ -9,8 +11,21 @@ http_archive(
     ],
 )
 
+http_archive(
+    name = "bazel_gazelle",
+    sha256 = "62ca106be173579c0a167deb23358fdfe71ffa1e4cfdddf5582af26520f1c66f",
+    url = "https://github.com/bazelbuild/bazel-gazelle/releases/download/v0.23.0/bazel-gazelle-v0.23.0.tar.gz",
+)
+
 load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")
+load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies")
+load("//:deps.bzl", "go_dependencies")
+
+# gazelle:repository_macro deps.bzl%go_dependencies
+go_dependencies()
 
 go_rules_dependencies()
 
 go_register_toolchains(version = "1.16")
+
+gazelle_dependencies()

deps.bzl

@@ -0,0 +1,15 @@
+load("@bazel_gazelle//:deps.bzl", "go_repository")
+
+def go_dependencies():
+    go_repository(
+        name = "com_github_google_uuid",
+        importpath = "github.com/google/uuid",
+        sum = "h1:b4Gk+7WdP/d3HZH8EJsZpvV7EtDOgaZLtnaNGIu1adA=",
+        version = "v1.0.0",
+    )
+    go_repository(
+        name = "com_github_pborman_uuid",
+        importpath = "github.com/pborman/uuid",
+        sum = "h1:+ZZIw58t/ozdjRaXh/3awHfmWRbzYxJoAdNJxe/3pvw=",
+        version = "v1.2.1",
+    )

e2e/go/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "go_lib",
+    srcs = ["main.go"],
+    importpath = "github.com/slsa-framework/example-package/e2e/go",
+    visibility = ["//visibility:private"],
+    deps = ["@com_github_pborman_uuid//:uuid"],
+)
+
+go_binary(
+    name = "go",
+    embed = [":go_lib"],
+    visibility = ["//visibility:public"],
+)