build: move to a Cargo workspace

This is purely to let Cargo's dependency resolver do stuff for us, we do
not actually intend to build this stuff with Cargo to begin with.

Change-Id: I4c08d55595c7c27b7096375022581e1e34308a87

1 files changed, 26 insertions, 0 deletions

diff --git a/meson.build b/meson.build
index bcf0d06bc..596373c8c 100644
--- a/meson.build
+++ b/meson.build
@@ -545,6 +545,32 @@ if cxx.get_id() in ['clang', 'gcc']
   )
 endif
 
+# Until Meson 1.5¹, we can't just give Meson a Cargo.lock file and be done with it.
+# Meson will *detect* what dependencies are needed from Cargo files; it just won't
+# fetch them. The Meson 1.5 feature essentially internally translates Cargo.lock entries
+# to .wrap files, and that translation is incredibly straightforward, so let's just
+# use a simple Python script to generate the .wrap files ourselves while we wait for
+# Meson 1.5. Weirdly, it seems Meson will only detect dependencies from other
+# dependency() calls, so we have to specify lix-doc's two top-level dependencies,
+# rnix and rowan, manually, and then their dependencies will be recursively translated
+# into more dependency() calls.
+#
+# When Meson translates a Cargo dependency, the string passed to `dependency()` follows
+# a fixed format, which is important as the .wrap files' basenames must match the string
+# passed to `dependency()` exactly.
+# In Meson 1.4, this format is `$packageName-rs`. Meson 1.5 changes this to
+# `$packageName-$shortenedVersionString-rs`, because of course it does, but we'll cross
+# that bridge when we get there...
+#
+# [1]: https://github.com/mesonbuild/meson/commit/9b8378985dbdc0112d11893dd42b33b7bc8d1e62
+run_command(
+  python,
+  meson.project_source_root() / 'meson/cargo-lock-to-wraps.py',
+  meson.project_source_root() / 'Cargo.lock',
+  meson.project_source_root() / 'subprojects',
+  check : true,
+)
+
 if is_darwin
   configure_file(
     input : 'misc/launchd/org.nixos.nix-daemon.plist.in',