I am glad to announce, on behalf of the Merlin team, the release of Merlin 3.4.0

which brings some major changes in the way configuration is handled.

As you might know, Merlin reads its configuration from the closest .merlin file

to the source file being edited. These files tell merlin where to find other

source files and build artifacts, but also which flags should be passed to the

compiler, which syntax extensions are enabled and which packages are used by the

project.

In this setting the configuration is the same for all the source files of a

folder, regardless of their specificities. In other words, the configuration

loaded for a single source file contains the union of the dependencies of this

file and of all its siblings which is not an optimal behavior.

Starting with version 3.4.0 merlin will ship with two packages: merlin and

dot-merlin-reader which, as the name suggests, reads configuration from .merlin

files. Both are necessary for proper function.

When a .merlin file is present in the source folder the Merlin server will start

a dot-merlin-reader process and communicate with it via standard input and

output following a simple protocol. These processes are halted with the server.

This change should not have any visible impact on users’ workflows as long as

the dot-merlin-reader binary is correctly installed and in the path. (which

should be the case in opam-based setups)

This change in itself will not solve the granularity problem mentioned earlier,

but it paves the way for such improvements: in a near-future Dune will stop

generating .merlin files and Merlin will obtain file-based configuration

directly from the build system using the same protocol as the one used by

dot-merlin-reader.

Changelog

   + merlin binary

       - fix completion of pattern matchings with exception patterns (#1169)

       - delegate configuration reading to external programs via a simple protocol

        and create a new package dot-merlin-reader with a binary that reads

        .merlin files. (#1123, #1152)