Allow to use recursion in Starlark

[maximyurchuk]

Description of the problem / feature request:

Allow to use recursion in Starlark. Instead of just detecting recursion maybe its better to limit Starlark stacksize.

Feature requests: what underlying problem are you trying to solve with this feature?

I trying to write my own .bzl files for building C++ code, but native functions is not well documented, because of that I'm just printing variables in my rules for exploration. But I've got an problem with writing generic function, which can dump object content in Starlark, because of lack of recursion.

My implementation of printing function for debug puproses:
my_rule.bzl:

def dump(obj, indent):
    for field in dir(obj):
        attr_value =  getattr(obj, field)
        attr_value_type =  type(getattr(obj, field))
        print(indent, attr_value_type,  field, ": ", )
        dump(attr_value, indent + "  ")
 

def _my_rule(ctx):
    dump(ctx.attr.input.output_groups, "")

my_rule = rule(
    implementation = _my_rule,
    attrs = {
        "input": attr.label(allow_single_file = True),
    },
)

BUILD:

package(default_visibility = ["//visibility:public"])

load("//:my_rule.bzl", "my_rule")


cc_library(
    name = "bar",
    srcs = ["main.cc"],
)

my_rule(
	name = "dump",
	input = ":bar",
)

With this code I've get an error:

Recursion was detected when calling 'dump' from 'dump'

What operating system are you running Bazel on?

Windows 10 x64

What's the output of bazel info release?

release 0.29.0rc5

Any other information, logs, or outputs that you want to share?

Bazel-discuss group thread

[laurentlb]

See discussion here: bazelbuild/starlark#97
and PR: #11822

[brandjon]

Another practical use case: #8921.

[sgowroji]

Hi there! We're doing a clean up of old issues and will be closing this one. Please reopen if you’d like to discuss anything further. We’ll respond as soon as we have the bandwidth/resources to do so.

[cpsauer]

IMO this would still be valuable! Worth keeping open?

[gsaraf]

We are having to overcome this now as well. We need to run code in a non-bazel use of Starlark that merges dictionaries. The workaround of using a queue for dictionaries to merge is significantly more confusing.