[Safe-logging] Verify member reference type parameters when cast to functional interface

[aldexis]

Before this PR

Passing a member reference as a lambda will currently not catch cases where the type it gets passed to has different requirements around safety of the return or parameter types.

After this PR

==COMMIT_MSG==
[Safe-logging] Verify member reference type parameters when cast to functional interface
==COMMIT_MSG==

This is done by comparing the safety between the method reference and the functional interface it gets cast into, and verifying that:

• The interface's return type safety is less safe than the method reference
  • This means you can do e.g. Supplier<@Unsafe String> f = this::fun when fun returns @Safe, but not @Supplier<@Safe String> f = this::fun when fun returns @Unsafe, as in the latter case, you would then start using the unsafe result from fun as safe when calling f
• The interface's argument's type safety is more safe than the method reference
  • This means you can do e.g. Consumer<@Safe String> f = this::fun when fun takes an @Unsafe, but not Consumer<@Unsafe String> f = this::fun when fun takes a @Safe, as otherwise calling f.accept(s) would let you pass an unsafe string to fun

To summarize:
Allowed

import com.palantir.logsafe.*;
import java.util.function.*;

class Test {
  Supplier<@Unsafe String> func = this::fun;

  @Safe
  String fun() {
    return "safe";
  }
}

import com.palantir.logsafe.*;
import java.util.function.*;

class Test {
  Consumer<@Safe String> func = this::fun;

  void fun(@Unsafe Object ob) {}
}

Forbidden

import com.palantir.logsafe.*;
import java.util.function.*;

class Test {
  Supplier<@Safe String> func = this::fun;

  @Unsafe
  String fun() {
    return "unsafe";
  }
}

import com.palantir.logsafe.*;
import java.util.function.*;

class Test {
  Consumer<@Unsafe String> func = this::fun;

  void fun(@Safe Object ob) {}
}

Possible downsides?

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Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

[Safe-logging] Verify member reference type parameters when cast to functional interface

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[carterkozak]

If we use state.reportMatch(, we can report problems with the return type as well as parameters in the same evaluation. It's not really the standard way we like to use error-prone, but I do find it helpful to describe all the issues at once for the safelogging check specifically

[aldexis]

Great idea indeed!

[carterkozak]

Should we check if ASTHelpers.getType(tree) returns null or findDescriptorType returns null and exit early?

[aldexis]

Good call!

[carterkozak]

Fantastic work, I especially appreciate the inline comments!

[carterkozak]

Feel free to add "merge-when-ready" if you're ready to release this

[autorelease3]

Released 6.16.0