Split cbindgen to separate build, support external version

The problem is building bindgen as part of our single run
locks serde to way old versions, and I want to use newer versions.

Since Fedora will now again ship a `cbindgen` package, let's
also support using it if we find it, saving ourselves
the cost of building it.

For distros that don't ship it (e.g. CentOS) for CI purposes
we build it.  For downstream builds that are offline, rather
than vendor the cbindgen sources like we do with our main Rust,
let's just vendor the `rpmostree-rust.h` file as was suggested
in https://bugzilla.redhat.com/show_bug.cgi?id=1608670

Closes: #1557

Closes: #1573
Approved by: jlebon

Makefile-rpm-ostree.am

@@ -84,6 +84,16 @@ if BUILDOPT_NEW_NAME
 INSTALL_DATA_HOOKS += install-bin-hook
 endif
 
+if !HAVE_PREBUILT_CBINDGEN
+if !HAVE_EXTERNAL_CBINDGEN
+rpmostree-bindgen: bindgen/Cargo.toml bindgen/src/main.rs
+	cd $(top_srcdir)/bindgen && \
+	export CARGO_TARGET_DIR=@abs_top_builddir@/bindgen-target && \
+	$(cargo) build --verbose && \
+	ln -sf $${CARGO_TARGET_DIR}/debug/rpmostree-bindgen $(abs_top_builddir)/rpmostree-bindgen
+endif
+endif
+
 librpmostree_rust_path = @abs_top_builddir@/target/@RUST_TARGET_SUBDIR@/librpmostree_rust.a
 # If the target directory exists, and isn't owned by our uid,
 # we use --frozen this happens with the `make && sudo make install`
@@ -98,11 +108,17 @@ $(librpmostree_rust_path): Makefile $(LIBRPMOSTREE_RUST_SRCS)
 	  $(cargo) build --verbose $${frozen} $(CARGO_RELEASE_ARGS)
 EXTRA_DIST += $(LIBRPMOSTREE_RUST_SRCS) rust/Cargo.lock
 
-# See rust/build.rs - it uses cbindgen as part of the Rust build
+# Generate bindings from Rust to C
+if !HAVE_PREBUILT_CBINDGEN
+if HAVE_EXTERNAL_CBINDGEN
 rpmostree-rust.h: $(librpmostree_rust_path)
-	$(AM_V_GEN) src=$$(find @abs_top_builddir@/target/@RUST_TARGET_SUBDIR@/ -name 'rpmostree-rust.h') && \
-	  test -n "$${src}" && ln -sfr "$${src}" rpmostree-rust.h
+	$(AM_V_GEN) cbindgen -c rust/cbindgen.toml -o $@ $(top_srcdir)/rust
+else
+rpmostree-rust.h: $(librpmostree_rust_path) rpmostree-bindgen
+	$(AM_V_GEN) ./rpmostree-bindgen $(top_srcdir)/rust
+endif
 BUILT_SOURCES += rpmostree-rust.h
+endif
 
 rpm_ostree_CFLAGS += $(PKGDEP_RPMOSTREE_RS_CFLAGS)
 rpm_ostree_LDADD += $(librpmostree_rust_path) $(PKGDEP_RPMOSTREE_RS_LIBS)

bindgen/.gitignore

@@ -0,0 +1,2 @@
+Cargo.lock
+target

bindgen/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "rpmostree-bindgen"
+version = "0.1.0"
+authors = ["Colin Walters <[email protected]>"]
+
+[dependencies]
+cbindgen = "0.6.3"
+
+# Might as well keep these from the main Rust source
+[profile.release]
+panic = "abort"
+debug = true

rust/build.rs → bindgen/src/main.rs

@@ -4,16 +4,14 @@
 extern crate cbindgen;
 
 fn run() -> Result<(), String> {
-    let out_dir_v = std::env::var("OUT_DIR").expect("OUT_DIR is unset");
-    let out_dir = std::path::Path::new(&out_dir_v);
+    let args: Vec<String> = std::env::args().collect();
+    let rustdir = std::path::Path::new(&args[1]);
+    let out = std::path::Path::new("rpmostree-rust.h");
 
-    // First, output our dependencies https://doc.rust-lang.org/cargo/reference/build-scripts.html
-    println!("cargo:rerun-if-changed=cbindgen.toml");
-
-    let bindings = cbindgen::generate(std::path::Path::new(".")).map_err(|e| e.to_string())?;
+    let bindings = cbindgen::generate(rustdir).map_err(|e| e.to_string())?;
     // This uses unwraps internally; it'd be good to submit a patch
     // to add a Result-based API.
-    bindings.write_to_file(out_dir.join("rpmostree-rust.h"));
+    bindings.write_to_file(out);
     Ok(())
 }
 

configure.ac

@@ -205,6 +205,17 @@ AS_IF([test -z "$cargo"], [AC_MSG_ERROR([cargo is required for --enable-rust])])
 AC_PATH_PROG([rustc], [rustc])
 AS_IF([test -z "$rustc"], [AC_MSG_ERROR([rustc is required for --enable-rust])])
 
+dnl https://github.com/projectatomic/rpm-ostree/pull/1573
+dnl We support 3 modes for bindgen:
+dnl  - External /usr/bin/cbindgen (Fedora + CI)
+dnl  - Downloading it from crates.io (CentOS + CI builds)
+dnl  - Not running it at all, and using a pre-built rpmostree-rust.h (Koji)
+AS_IF([test -d "${srcdir}"/rust/vendor],
+      [cbindgen=dist],
+      [AC_PATH_PROG([cbindgen], [cbindgen])])
+AM_CONDITIONAL(HAVE_PREBUILT_CBINDGEN, [test "${cbindgen}" = "dist"])
+AM_CONDITIONAL(HAVE_EXTERNAL_CBINDGEN, [test -n "${cbindgen}" && test "${cbindgen}" != dist])
+
 AC_MSG_CHECKING(whether to build in debug mode)
 debug_release=release
 if $(echo $CFLAGS |grep -q -E "(-O0|-Og)"); then
@@ -271,4 +282,5 @@ echo "
     bubblewrap:                              $with_bubblewrap
     gtk-doc:                                 $enable_gtk_doc
     rust:                                    $rust_debug_release
+    cbindgen:                                ${cbindgen:-internal}
 "

packaging/make-git-snapshot.sh

@@ -51,4 +51,11 @@ j["files"] = {f:c for f, c in j["files"].items() if not f.startswith("curl/")}
 open(sys.argv[1], "w").write(json.dumps(j))' vendor/curl-sys/.cargo-checksum.json
  tar --transform="s,^,${PKG_VER}/rust/," -rf ${TARFILE_TMP} * .cargo/
  )
+
+# And finally, vendor rpmostree-rust.h; it's generated by cbindgen,
+# and it's easier than vendoring all of the source for that too.
+# This is currently the *only* generated file we treat this way. See also
+# https://github.com/projectatomic/rpm-ostree/pull/1573
+(cd ${srcdir} && tar --transform "s,^,${PKG_VER}/," -rf ${TARFILE_TMP} rpmostree-rust.h)
+
 mv ${TARFILE_TMP} ${TARFILE}

rust/Cargo.toml

@@ -2,7 +2,6 @@
 name = "rpmostree-rust"
 version = "0.1.0"
 authors = ["Colin Walters <[email protected]>"]
-build = "build.rs"
 
 [dependencies]
 serde = "1.0"
@@ -17,9 +16,6 @@ tempfile = "3.0.3"
 openat = "0.1.15"
 curl = "0.4.14"
 
-[build-dependencies]
-cbindgen = "0.6.3"
-
 [lib]
 name = "rpmostree_rust"
 path = "src/lib.rs"