OCaml Changelog

The Ppxlib dev team is happy to announce the release of ppxlib.0.33.0.

This release's main feature is a series of improvement to flags controlling unused value/module/type warnings silencing. The ppxlib driver generates warning silencing items to prevent [@@deriving ...] generated code to trigger unused code warnings. Three warnings are disabled that way:

• Warning 32: unused value
• Warning 60: unused module
• Warning 34: unused type The first two are disabled for values and modules generated by the deriver while the third is disabled for the types in the type declaration to which the [@@deriving ...] attribute is attached. This feature was added a long time ago to avoid manually disabling those warnings when working with derivers that generate a set of values and modules only to use a subset of those. Alternatively, the unused type warning silencing was added to allow defining an alias type only to be consumed by a deriver (e.g., type error = [`Not_found | `Invalid_arg] [@@deriving to_string]). We since then believe that we should not disable warnings lightly, as this behaviour makes it difficult to find and remove deadcode. The right approach in those situations should be to fix the PPX derivers so that they are more configurable and can be used without triggering such warnings. We will start to move toward removing this feature, but since it is still useful in some places, we came up with a plan to do this iteratively. In ppxlib.0.31.0 we added the -unused-code-warnings driver flag and the ?unused_code_warnings Deriving.V2.make optional argument to control whether to silence Warnings 32 and 60. When both are set to true, by the user and the deriver authors, the warnings are not silenced. As of ppxlib.0.33.0, these also control the silencing of Warning 34 (unused type). force can now be passed to the -unused-code-warnings flag in order to disable warnings silencing, regardless of the derivers opting in. This allows users to test whether their codebase and their set of derivers rely on warning silencing or not and to use those results to eliminate deadcode and/or report issues upstream to the derivers they use. We also added a separate -unused-type-warnings flag that works similarly to -unused-code-warnings (i.e., depends on the value of the ?unused_code_warnings argument), but it only controls Warning 34 silencing, as it turns out it is less likely to cause unwanted warnings than with the other two. This will allow users to disable it more easily, without having to deal with Warnings 32 and 60 straight away. We want to encourage users to try those on their codebase in order to see the impact it has. Did you have deadcode lying around that slipped past undetected? Does this trigger unwanted warnings because of deriver's generated code? The plan is to give the ecosystem some time to try those features and adapt by fixing individual derivers and flipping setting ?unused_code_warnings to true as they do. After a while, we will swap the default value of the driver flag to true so that only derivers that haven't opted in will enable warning silencing. Then as time goes we will swap the default of the Deriving.make argument so that derivers will instead have to explicitly opt out to get the warning silencing. Finally, once we are confident the ecosystem is in a good enough state, we will remove this feature altogether.

ppxlib.0.33.0 also comes with a couple of new features for PPX authors:

• A couple new Ast_builder functions: elist_tail and plist_tail that can be used to build list expressions and patterns with a custom tail: elist_tail [expr1; expr2] tail_expr returns the expression for expr1::expr2::tail_expr.
• Context_free.special_function', a new version of special_function that allows passing a Longident.t directly rather that relying on parsing the string argument to a Longident.t.

Finally, the release includes a few bug fixes to Longident.parse and Code_path.main_module_name and fixes the location-check flag so it is not required to also pass -check to enable location checks. It also fixes the 5.2 migrations locations, as we used to build nodes with inconsistent locations when migrating Pexp_function nodes.

We would like to thank our external contributors who have been a huge part of this release: @octachron, @vg-b, and @jchavarri, and a special mention to @mbarbin, who has not only contributed a lot to the warning silencing features but has been extensively testing and providing very useful feedback on them.

And of course, as usual, we'd like to thank the OCaml Software Foundation who has been funding my work on Ppxlib and on this release, making all of this possible!

The ppxlib team is happy to announce the release of ppxlib.0.32.1.

The main feature of this release is of course the support for the upcoming OCaml 5.2 release. Starting with this version you'll be able to use ppx with the latest compiler.

The feature also comes with a small follow up improvement to the 0.32.0 error reporting changes that simplifies how exception thrown from context free rewriting are handled. The errors will now be inserted where the generated code would have been instead of appended to the whole AST. This should lead to a better error reporting from the compiler as it will now report errors in order of their position in the code.

We'd like to thank the OCaml Software Foundation once again as they funded the vast majority of the work for this release.

The ppxlib dev team is happy to announce the release of ppxlib.0.32.0.

The main feature of this release, implemented by @burnleydev1 during their Outreachy internship, is a huge improvement of the handling of located exceptions raised by ppx-es. Whenever a rewrite of the AST throws such an exception, the ppxlib driver catches it and resumes the rewriting using the latest valid AST it knows of. All caught exceptions are appended to the final AST as [%%ocaml.error ..] nodes. This means the driver returns a valid AST instead of one composed of a single error node corresponding to the first raised exception. This leads to a much better experience for ppx users as merlin now has a valid AST to work with when this happens, allowing it to properly function, reporting all errors, from ppx-es or otherwise. Note that despite this change we still recommend ppx authors to embed errors in the rewritten AST rather than throw exceptions.

The release also comes with a few bug fixes on longident parsing or windows compatibility and a new simplified API for ppx authors using attributes as flags (i.e. attributes without payloads such as [@ignore] for instance).

We'd like to thank our external contributors for this release:

• @burnleydev1 for their improvement of the driver exception handling
• @dianaoigo for their addition of the new attribute flags API
• @jonahbeckford for their fix of the windows compatibility

We'd also like to thank the OCaml Software Foundation who has been funding my work on this release.

We're happy to announce the release of Ppxlib 0.31.0. Shortly after OCaml 5.1.0 has been released, this Ppxlib release fixes a bug in the support of OCaml 5.1.0. Before that bug fix, the warnings about a generative/applicative mismatch between a functor creation and its application introduced by OCaml 5.1.0 were also triggered when that mismatch didn't exist.

Furthermore, the release contains a couple of bug fixes in the context of attributes.

We're also excited about two main enhancements. One allows authors of extension node rewriters to add a path argument to the extension node. That's excellent for hygiene since it allows the PPX to be explicit about modules rather than depending on its scope.

The other main enhancement allows an opt-in for compiler warnings about unused code generated by derivers (warnings w32 and w60). That opting in needs to happen on both sides of the deriver, the writer side and the user side. Opting in to those code warnings will help to clean up unused code, leading to performance improvements in compilation and editor support.

We're excited to announce the release of Ppxlib 0.30.0! It comes with support for OCaml 5.1, various enhancements, and bug fixes.

For PPX writing, Ast_pattern now offers additional utility functions, while metaquot benefits from improved error reporting.

PPX usage sees better compatibility with OCaml trunk, thanks to the Driver's improved Parsetree version recognition. This allows for compatibility with both trunk and stable OCaml versions concurrently.

Finally, this release enhances Ppxlib's compatibility with ReScript, introducing "ns" and "res" as reserved namespaces.