CHANGES:

- Restricted the set of variables available for expansion in the destination
  filename of `install` stanza to simplify implementation and avoid dependency
  cycles. (ocaml/dune#2073, @aalekseyev, @diml)

- [menhir] call menhir from context root build_dir (ocaml/dune#2067, @ejgallego,
  review by @diml, @rgrinberg)

- [coq] Add `coq.pp` stanza to help with pre-processing of grammar
  files (ocaml/dune#2054, @ejgallego, review by @rgrinberg)

- Add a new more generic form for the *promote* mode: `(promote
  (until-clean) (into <dir>))` (ocaml/dune#2068, @diml)

- Allow to promote only a subset of the targets via `(promote (only
  <pred>))`. For instance: `(promote (only *.mli))` (ocaml/dune#2068, @diml)

- Improve the behavior when a strict subset of the targets of a rule is already
  in the source tree for projects using the dune language < 1.10 (ocaml/dune#2068, fixes
  ocaml/dune#2061, @diml)

- With lang dune >= 1.10, rules in standard mode are no longer allowed to
  produce targets that are present in the source tree. This has been a warning
  for long enough (ocaml/dune#2068, @diml)

- Allow %{...} variables in pps flags (ocaml/dune#2076, @mlasson review by @diml and
  @aalekseyev).

- Add a 'cookies' option to ppx_rewriter/deriver flags in library stanzas. This
  allow to specify cookie requests from variables expanded at each invocation of
  the preprocessor. (ocaml/dune#2106, @mlasson @diml)

- Add more opam metadata and use it to generate `.opam` files. In particular, a
  `package` field has been added to specify package specific information.
  (ocaml/dune#2017, ocaml/dune#2091, @avsm, @jonludlam, @rgrinberg)

- Clean up the special support for `findlib.dynload`. Before, Dune would simply
  match on the library name. Now, we only match on the findlib package name when
  the library doesn't come from Dune. Someone writing a library called
  `findlib.dynload` with Dune would have to add `(special_builtin_support
  findlib_dynload)` to trigger the special behavior. (ocaml/dune#2115, @diml)

- Install the `future_syntax` preprocessor as `ocaml-syntax-shims.exe` (ocaml/dune#2125,
  @rgrinberg)

- Hide full command on errors and warnings in development and show them in CI.
  (detected using the `CI` environment variable). Commands for which the
  invocation might be omitted must output an error prefixed with `File `. Add an
  `--always-show-command-line` option to disable this behavior and always show
  the full command. (ocaml/dune#2120, fixes ocaml/dune#1733, @rgrinberg)

- In `dune-workspace` files, add the ability to choose the host context and to
  create duplicates of the default context with different settings. (ocaml/dune#2098,
  @TheLortex, review by @diml, @rgrinberg and @aalekseyev)

- Add support for hg in `dune subst` (ocaml/dune#2135, @diml)

- Don't build documentation for implementations of virtual libraries (ocaml/dune#2141,
  fixes ocaml/dune#2138, @jonludlam)

- Fix generation of the `-pp` flag in .merlin (ocaml/dune#2142, @rgrinberg)

- Make `dune subst` add a `(version ...)` field to the `dune-project`
  file (ocaml/dune#2148, @diml)

- Add the `%{os_type}` variable, which is a short-hand for
  `%{ocaml-config:os_type}` (ocaml/dune#1764, @diml)

- Allow `enabled_if` fields in `library` stanzas, restricted to the
  `%{os_type}`, `%{model}`, `%{architecture}`, `%{system}` variables (ocaml/dune#1764,
  ocaml/dune#2164 @diml, @rgrinberg)

- Fix `chdir` on external and source paths. Dune will also fail gracefully if
  the external or source path does not exist (ocaml/dune#2165, fixes ocaml/dune#2158, @rgrinberg)

- Support the `.cc` extension fro C++ sources (ocaml/dune#2195, fixes ocaml/dune#83, @rgrinberg)

- Run `ocamlformat` relative to the context root. This improves the locations of
  errors. (ocaml/dune#2196, fixes ocaml/dune#1370, @rgrinberg)

- Fix detection of `README`, `LICENSE`, `CHANGE`, and `HISTORY` files. These
  would be undetected whenever the project was nested in another workspace.
  (ocaml/dune#2194, @rgrinberg)

- Fix generation of `.merlin` whenever there's more than one stanza with the
  same ppx preprocessing specification (ocaml/dune#2209 ,fixes ocaml/dune#2206, @rgrinberg)

- Fix generation of `.meriln` in the presence of the `copy_files` stanza and
  preprocessing specifications of other stanazs. (ocaml/dune#2211, fixes ocaml/dune#2206,
  @rgrinberg)

CHANGES:

- Restricted the set of variables available for expansion in the destination
  filename of `install` stanza to simplify implementation and avoid dependency
  cycles. (ocaml/dune#2073, @aalekseyev, @diml)

- [menhir] call menhir from context root build_dir (ocaml/dune#2067, @ejgallego,
  review by @diml, @rgrinberg)

- [coq] Add `coq.pp` stanza to help with pre-processing of grammar
  files (ocaml/dune#2054, @ejgallego, review by @rgrinberg)

- Add a new more generic form for the *promote* mode: `(promote
  (until-clean) (into <dir>))` (ocaml/dune#2068, @diml)

- Allow to promote only a subset of the targets via `(promote (only
  <pred>))`. For instance: `(promote (only *.mli))` (ocaml/dune#2068, @diml)

- Improve the behavior when a strict subset of the targets of a rule is already
  in the source tree for projects using the dune language < 1.10 (ocaml/dune#2068, fixes
  ocaml/dune#2061, @diml)

- With lang dune >= 1.10, rules in standard mode are no longer allowed to
  produce targets that are present in the source tree. This has been a warning
  for long enough (ocaml/dune#2068, @diml)

- Allow %{...} variables in pps flags (ocaml/dune#2076, @mlasson review by @diml and
  @aalekseyev).

- Add a 'cookies' option to ppx_rewriter/deriver flags in library stanzas. This
  allow to specify cookie requests from variables expanded at each invocation of
  the preprocessor. (ocaml/dune#2106, @mlasson @diml)

- Add more opam metadata and use it to generate `.opam` files. In particular, a
  `package` field has been added to specify package specific information.
  (ocaml/dune#2017, ocaml/dune#2091, @avsm, @jonludlam, @rgrinberg)

- Clean up the special support for `findlib.dynload`. Before, Dune would simply
  match on the library name. Now, we only match on the findlib package name when
  the library doesn't come from Dune. Someone writing a library called
  `findlib.dynload` with Dune would have to add `(special_builtin_support
  findlib_dynload)` to trigger the special behavior. (ocaml/dune#2115, @diml)

- Install the `future_syntax` preprocessor as `ocaml-syntax-shims.exe` (ocaml/dune#2125,
  @rgrinberg)

- Hide full command on errors and warnings in development and show them in CI.
  (detected using the `CI` environment variable). Commands for which the
  invocation might be omitted must output an error prefixed with `File `. Add an
  `--always-show-command-line` option to disable this behavior and always show
  the full command. (ocaml/dune#2120, fixes ocaml/dune#1733, @rgrinberg)

- In `dune-workspace` files, add the ability to choose the host context and to
  create duplicates of the default context with different settings. (ocaml/dune#2098,
  @TheLortex, review by @diml, @rgrinberg and @aalekseyev)

- Add support for hg in `dune subst` (ocaml/dune#2135, @diml)

- Don't build documentation for implementations of virtual libraries (ocaml/dune#2141,
  fixes ocaml/dune#2138, @jonludlam)

- Fix generation of the `-pp` flag in .merlin (ocaml/dune#2142, @rgrinberg)

- Make `dune subst` add a `(version ...)` field to the `dune-project`
  file (ocaml/dune#2148, @diml)

- Add the `%{os_type}` variable, which is a short-hand for
  `%{ocaml-config:os_type}` (ocaml/dune#1764, @diml)

- Allow `enabled_if` fields in `library` stanzas, restricted to the
  `%{os_type}`, `%{model}`, `%{architecture}`, `%{system}` variables (ocaml/dune#1764,
  ocaml/dune#2164 @diml, @rgrinberg)

- Fix `chdir` on external and source paths. Dune will also fail gracefully if
  the external or source path does not exist (ocaml/dune#2165, fixes ocaml/dune#2158, @rgrinberg)

- Support the `.cc` extension fro C++ sources (ocaml/dune#2195, fixes ocaml/dune#83, @rgrinberg)

- Run `ocamlformat` relative to the context root. This improves the locations of
  errors. (ocaml/dune#2196, fixes ocaml/dune#1370, @rgrinberg)

- Fix detection of `README`, `LICENSE`, `CHANGE`, and `HISTORY` files. These
  would be undetected whenever the project was nested in another workspace.
  (ocaml/dune#2194, @rgrinberg)

- Fix generation of `.merlin` whenever there's more than one stanza with the
  same ppx preprocessing specification (ocaml/dune#2209 ,fixes ocaml/dune#2206, @rgrinberg)

- Fix generation of `.merlin` in the presence of the `copy_files` stanza and
  preprocessing specifications of other stanazs. (ocaml/dune#2211, fixes ocaml/dune#2206,
  @rgrinberg)

- Run `refmt` from the context's root directory. This improves error messages in
  case of syntax errors. (ocaml/dune#2223, @rgrinberg)

- In .merlin files, don't pass `-dump-ast` to the `future_syntax` preprocessor.
  Merlin doesn't seem to like it when binary AST is generated by a `-pp`
  preprocessor. (ocaml/dune#2236, @aalekseyev)

- `dune install` will verify that all files mentioned in all .install files
  exist before trying to install anything. This prevents partial installation of
  packages (ocaml/dune#2230, @rgrinberg)