Start analyzing & evaluating meta

[shantanu-sardesai]

Description

We should begin analyzing the metadata as well. At present, we store the metadata source directly without proper analysis or evaluation, resulting in the following code executing despite being semantically incorrect:

user=> (def ^{:pp #(println foo)} bar 0)
#'user/bar

user=> (meta bar)
nil

user=> (meta #'bar)
{:jank/source {:file "/var/folders/xd/9v1dcg0d46l7d19830vq0lhc0000gn/T/jank-repl-fYkERF", :start {:offset 27, :line 1, :col 28}, :end {:offset 30, :line 1, :col 31}}, :pp (fn* [] (println foo))}

user=> ((-> #'bar meta :pp))
Uncaught exception: Invalid call with 0 args to: (fn* [] (println foo))

There are two issues being highlighted here:

1. Although the foo symbol is not in scope during the definition of the bar var, jank does not emit any analysis failure warnings.
2. Due to lack of evaluation currently the :pp key in the metadata of the bar var contains the source code instead of a compiled function, preventing us from invoking the function.

Goal

Within the scope of this PR I wish to start analyzing the metadata such that the above cases behave as would be expected:

user=> (def ^{:pp #(println foo)} bar 0)
─ analyze/unresolved-symbol ────────────────────────────────────────────────────────────────────────
error: Unable to resolve symbol 'foo'.

─────┬──────────────────────────────────────────────────────────────────────────────────────────────
     │ /var/folders/xd/9v1dcg0d46l7d19830vq0lhc0000gn/T/jank-repl-hKkVT2
─────┼──────────────────────────────────────────────────────────────────────────────────────────────
  1  │ (def ^{:pp #(println foo)} bar 0)
     │                      ^^^ Found here.
─────┴──────────────────────────────────────────────────────────────────────────────────────────────

user=> (def foo 0)
#'user/foo

user=> (def ^{:pp #(println foo)} bar 0)
#'user/bar

user=> (meta #'bar)
{:jank/source {:file "/var/folders/xd/9v1dcg0d46l7d19830vq0lhc0000gn/T/jank-repl-hKkVT2", :start {:offset 27, :line 1, :col 28}, :end {:offset 30, :line 1, :col 31}}, :pp #object [user/user-fn-53 jit_function 0x10ec383f8]}

user=> ((-> #'bar meta :pp))
0
nil

---

Fixes

Resolves #197.

[shantanu-sardesai]

Currently the following doesn't work:

(let* [foo 42]
  (def ^{:pp #(println foo)} bar 0)
  (assert (= ((-> #'bar meta :pp)) 42)))

But before I dive deeper I thought best align on where to store the analysis results for meta.

[jeaye]

Good start, Shantanu. Your overall unwrap usage is lacking a lot of necessary discipline. The testing strategy will need some more detailed planning, too, since this opens up a lot of doors. Finally, IR gen has not been updated, so none of this will work when wrapped in a function or AOT compiled.

[jeaye]

This is not how new tests should be added. Each test should have a dedicated test file, describing what it's testing. Also, we now have possibilities for extra errors, which come from analyzing meta. That needs to be tested.

[jeaye]

This is lazy and not safe (because we don't know that meta contains a value). Look at line 281 for not only the variable you should use, but how to safely grab this value.

[shantanu-sardesai]

I've chosen to wrap the unwrap in an is_some block so that I won't even bother calling eval when there is no meta available.

[jeaye]

This will fail if you wrap it in a function or let*, since IR gen has not been updated.