[new release] dune (1.8.0)

[rgrinberg]

CHANGES:

• Clean up watch mode polling loop: improves signal handling and error handling
  during polling (Control+C handling dune#1912, fix watch mode: assertion failed when directory does not exist dune#1907, fix Ctrl+C doesn't work well in watch mode dune#1671, @aalekseyev)

• Change status messages during polling to be one-line, so that the messages are
  correctly erased by ^K. (Control+C handling dune#1912, @aalekseyev)

• Add support for .cxx extension for C++ stubs (Add cxx extension for C++ stubs dune#1831, @rgrinberg)

• Add DUNE_WORKSPACE variable. This variable is equivalent to setting
  --workspace in the command line. (Add DUNE_WORKSPACE env var dune#1711, fix Expand environment variables everywhere dune#1503, @rgrinberg)

• Add c_flags and cxx_flags to env profile settings (Add c_flags and cxx_flags to env profile settings dune#1700 and Command 'dune' not found, but can be installed with dune#1800,
  @gretay-js)

• Format dune printenv output (Format printenv output dune#1867, fix dune printenv doesn't respect formatting dune#1862, @emillon)

• Add the (promote-into <dir>) and `(promote-until-clean-into

  )` modes for `(rule ...)` stanzas, so that files can be promoted in another directory than the current one. For instance, this is used in merlin to promote menhir generated files in a directory that depends on the version of the compiler (Add the (promote*-into <dir>) rule modes dune#1890, @diml)

• Improve error message when dune subst fails (Improve error message when dune subst fails dune#1898, fix dune subst is looking for an opam.opam file and failing dune#1897, @rgrinberg)

• Add more GC counters to catapult traces (fix908, @rgrinberg)

• Add a preprocessor shim for the let+ syntax of OCaml 4.08 (Compatibility let syntax dune#1899,
  implements [RFC] Compatibility let+ syntax dune#1891, @diml)

• Fix generation of .merlin files on Windows. \ characters needed
  to be escaped (Fixes #366 - Escape backslashes .merlin FLG lines dune#1869, @mlasson)

• Fix 0 error code when $ dune format-dune-file fails. (Fix #1914 dune#1915, fix dune format should set error code different from 0 if parsing fails dune#1914,
  @rgrinberg)

• Configurator: deprecated query_expr and introduced query_expr_err which is
  the same but with a better error in case it fails. ([configurator] Return pkg-config error to clients of new query API. dune#1886, @ejgallego)

[camelus]

☀️ All lint checks passed 234e8d2

• These packages passed lint tests: dune.1.8.0

---

☀️ Installability check (10708 → 10709)

• new installable packages (1): dune.1.8.0

[ghost]

@rgrinberg, do you mind including this pr in 1.8.0? We were just trying the (promote-into ...) mode in merlin and we hit a limitation due to this bug