1674224 - JNI annotation processor should generate hint comments to help developers determine native method signatures

Status: RESOLVED FIXED

(GeckoView :: General, task, P1)

Description

[(No longer employed by Mozilla) Aaron Klotz]

When I first started working with our JNI stuff, one thing I noticed that increases difficulty is figuring out what a native method signature should actually be. This resulted in a bit of trial and error until I got something that built.

Our annotation processor already has an idea about what native method signatures should be; we just need to spit that information out as a comment that describes a sample signature for the developer-supplied native method(s).

I have some test patches, so I'll assign myself...

Comment 1

[(No longer employed by Mozilla) Aaron Klotz]

Attachment: Sample header

Comment 2

[(No longer employed by Mozilla) Aaron Klotz]

Attachment: Bug 1674224: Generate Java signature hints in JNI wrappers; r=#geckoview-reviewers

This patch adds some code to our annotation processor that produces comments in
our generated JNI headers to help the developer understand which types are
involved. There are two new types of comments:

• For generated methods from native to Java, we produce a simplified Java method
  signature (sans package names) to help the caller disambiguate parameter
  types. This is helpful since the machine-readable method signature tend to
  use mozilla::jni::Object::Param instead of actual types (for the purposes of
  avoiding dependency hell, presumably).
• For Java to native methods, we produce a sample signature that is usable for
  the implementation of the native method.

While we did discuss some ideas about other locations where we could output this
data, I'd like to start with the generated header files for now. We can make
adjustments to the output location in future bugs.

I will be attaching an example of a generated header that contains these new
comments to the bug.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5e3ff421cf2a
Generate Java signature hints in JNI wrappers; r=geckoview-reviewers,agi

Comment 4

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/5e3ff421cf2a