Self-Referential Substitutions don't work

[troizky]

I'm using the example from documentation: https://github.com/lightbend/config/blob/master/HOCON.md#examples-of-self-referential-substitutions

A self-reference resolves to the value "below" even if it's part of a path expression. So for example:

foo : { a : { c : 1 } }
foo : ${foo.a}
foo : { a : 2 }

Here, ${foo.a} would refer to { c : 1 } rather than 2 and so the final merge would be { a : 2, c : 1 }.
Recall that for a field to be self-referential, it must have a substitution or value concatenation as its value. If a field has an object or array value, for example, then it is not self-referential even if there is a reference to the field itself inside that object or array.

And I'm getting crash:
terminate called after throwing an instance of 'hocon::bug_or_broken_exception' what(): resolve_substitutions() did not give us a resolved object
Also I'm getting crash in cases below:

a = {aa = abba}
a.aa = mama
b = ${a} { bb = mia }
# Everything below is failing
b.aa = mea
b.bb = culpa
b = { aa = mea, bb = culpa }
c = ${b.aa}
c = ${b.bb}

Looks like this library implementation doesn't follow the HOCON documentation...

[MikaelSmith]

The implementation is incomplete. I would appreciate any help finishing it for those cases.

[troizky]

Even the simplest testcase does not work:

  "a": {
    "b": 27
  },
  "obj": ${a}
  "val": ${obj.b}

Maybe this one is easier to fix?

[MikaelSmith]

That is likely HC-73. I'll take a quick look to see if I can figure out what's wrong, but don't have a ton of time to spend on it before I'm on vacation for 2 weeks.

[MikaelSmith]

This library was implemented to closely mirror the structure of https://github.com/lightbend/config. So tracing the exception I get with your simple test case back to https://github.com/puppetlabs/cpp-hocon/blob/master/lib/src/values/config_reference.cc#L75 and comparing to https://github.com/lightbend/config/blob/master/config/src/main/java/com/typesafe/config/impl/ConfigReference.java#L70, it looks like the fallback code at https://github.com/puppetlabs/cpp-hocon/blob/master/lib/src/values/config_reference.cc#L61 wasn't implemented. I'll try that out.

[MikaelSmith]

It looks like this might have actually been fixed recently in config v1.3.2. So there's some work to incorporate the fixes added. Update: I might be jumping to conclusions here; but this is the area where a fix will probably be needed. If it's not a fix in config 1.3.2, then the lookup_subst is failing somehow.

[troizky]

I've found bug in https://github.com/puppetlabs/cpp-hocon/blob/master/lib/src/values/simple_config_object.cc#L32, must be checking for non-empty.
Corresponding line in Java project: https://github.com/lightbend/config/blob/master/config/src/main/java/com/typesafe/config/impl/SimpleConfigObject.java#L364
Unfortunately 2 test cases are failing now...

[troizky]

Also found that method config_delayed_merge_object::resolve_substitutions was not implemented like here: https://github.com/lightbend/config/blob/master/config/src/main/java/com/typesafe/config/impl/ConfigDelayedMergeObject.java#L53

After fixing that I'm getting an exception 'should not be reached (merging non-simple_config_object)' in simple_config_object::merged_with_object on parsing following config:

    a = {aa = mama, bb = mia}
    b = ${a}
    b.aa = mea
    # below is failing
    b.bb = culpa

[troizky]

One more bug in https://github.com/puppetlabs/cpp-hocon/blob/master/lib/inc/internal/values/config_delayed_merge_object.hpp#L10, class config_delayed_merge_object did not inherit from class unmergeable like here: https://github.com/lightbend/config/blob/master/config/src/main/java/com/typesafe/config/impl/ConfigDelayedMergeObject.java#L21

[troizky]

Here is my suggested patch:
cpp-hocon.patch.gz

[troizky]

Open Merge Request #106

[MikaelSmith]

Thanks for digging into this! I'll work on reviewing the PRs.