fix(buck2): declare build_deps on docker_image as dep type

prelude-si/docker.bzl

@@ -50,7 +50,7 @@ docker_image = rule(
             doc = """Mapping of sources files to the relative directory in a Dockerfile context..""",
         ),
         "build_deps": attrs.list(
-            attrs.string(),
+            attrs.dep(),
             default = [],
             doc = """Buck2 targets that could be built in an image.""",
         ),
@@ -219,7 +219,7 @@ def docker_build_context(ctx: "context") -> DockerBuildContext.type:
         cmd.add(cmd_args(src, format = "{}=" + rel_path))
     for dep in ctx.attrs.build_deps or []:
         cmd.add("--dep")
-        cmd.add(dep)
+        cmd.add(dep.label.raw_target())
     cmd.add(context_tree.as_output())
 
     ctx.actions.run(cmd, category = "docker_build_context")

prelude-si/docker/docker_build_context_srcs_from_deps.bxl

@@ -60,7 +60,9 @@ docker_build_context_srcs_from_deps = bxl(
 )
 
 def _normalize_target_str(dep: str.type) -> str.type:
-    if dep.startswith("//"):
+    if dep.startswith("root//"):
+        return dep
+    elif dep.startswith("//"):
         return "root" + dep
     else:
         return "root//{}".format(dep)