rust/cbindgen: Revert Makefile to a more pre-cbindgen state

The modifications as part of the cbindgen commit caused issues
with distcheck, revert the Makefile to how it was with the Python
generator, but still using cbindgen.

Also always assume we'll include the generated headers in the
distribution archive to fix make distcheck from distribution
archives with headers included, but no cbindgen.

configure.ac

@@ -2460,26 +2460,36 @@ fi
     fi
 
     AC_CHECK_FILES([$srcdir/rust/gen], [have_rust_headers="yes"])
-    AC_DEFINE([HAVE_RUST_HEADERS],[1],[Enable Rust language])
-    AM_CONDITIONAL([HAVE_RUST_HEADERS], [test "x$have_rust_headers" = "xyes"])
+    AC_PATH_PROG(CBINDGEN, cbindgen, "no")
+    if test "x$CBINDGEN" != "xno"; then
+      cbindgen_version=$(cbindgen --version | cut -d' ' -f2-)
+      min_cbindgen_version="0.10.0"
+      AS_VERSION_COMPARE([$cbindgen_version], [$min_cbindgen_version],
+          [cbindgen_ok="no"],
+          [cbindgen_ok="yes"],
+          [cbindgen_ok="yes"])
+      if test "x$cbindgen_ok" != "xyes"; then
+        echo "  Warning: cbindgen must be at least version $min_cbindgen_version,"
+        echo "      found $cbindgen_version."
+        echo "  To update: cargo install --force cbindgen"
+        CBINDGEN="no"
+      else
+        have_rust_headers="no"
+      fi
+    fi
+
+    # Require cbindgen if generated headers are not bundled.
     if test "x$have_rust_headers" != "xyes"; then
-      AC_PATH_PROG(HAVE_CARGO_CBINDGEN, cbindgen, "no") 
-      if test "x$HAVE_CARGO_CBINDGEN" = "xno"; then
-        echo "  Warning: cbindgen not found, it is required to generate header files"
+      if test "x$CBINDGEN" = "xno"; then
+        echo "  Warning: cbindgen too old or not found, it is required to "
+        echo "      generate header files."
         echo "  To install: cargo install --force cbindgen"
         AC_MSG_ERROR([cbindgen required])
       fi
-      required_version=0.9.0
-      cbindgen_version=$(cbindgen --version | cut -d' ' -f2-)
-      lowest_version=$(printf '%s\n' $required_version $cbindgen_version | sort -t. -k 1,1n -k 2,2n -k 3,3n -k 4,4n | head -n1)
-      if test "x$lowest_version" != "x$required_version"; then
-        HAVE_CARGO_BINDGEN="no"
-        echo "  Warning: cbindgen must be at least version $required_version, version was $cbindgen_version, lowest version was $lowest_version"
-        echo "  To install: cargo install --force cbindgen"
-        AC_MSG_ERROR([incorrect cbindgen version])
-      fi
     fi
 
+    AM_CONDITIONAL([HAVE_RUST_HEADERS], [test "x$have_rust_headers" = "xyes"])
+    AM_CONDITIONAL([HAVE_CBINDGEN], [test "x$CBINDGEN" != "xno"])
     AM_CONDITIONAL([HAVE_CARGO_VENDOR], [test "x$have_cargo_vendor" != "xno"])
 
     AC_ARG_ENABLE(rust_strict,

rust/Makefile.am

@@ -1,7 +1,7 @@
 EXTRA_DIST =	src \
 		.cargo/config.in \
-                gen \
-                cbindgen.toml
+		cbindgen.toml \
+		gen/rust-bindings.h
 
 if HAVE_CARGO_VENDOR
 EXTRA_DIST +=	vendor
@@ -23,9 +23,11 @@ if RUST_CROSS_COMPILE
 RUST_TARGET = --target $(host_triplet)
 endif
 
-build-rust:
-	cd $(top_srcdir)/rust
-
+all-local:
+if HAVE_CBINDGEN
+	cbindgen --config $(abs_top_srcdir)/rust/cbindgen.toml \
+		--quiet --output $(abs_top_builddir)/rust/gen/rust-bindings.h
+endif
 if HAVE_CYGPATH
 	@rustup_home@ \
 		CARGO_HOME="$(CARGO_HOME)" \
@@ -40,30 +42,12 @@ else
 			--features "$(RUST_FEATURES)" $(RUST_TARGET)
 endif
 
-if HAVE_RUST_HEADERS
-
-all-local: build-rust
-	echo Rust headers available
-
-clean-local:
-	-rm -rf target
-
-distclean-local: clean-local
-	rm -rf vendor Cargo.lock
-
-else 
-
-all-local: gen-headers build-rust
-	$(info Generating rust headers)
-
 clean-local:
 	-rm -rf target gen
 
 distclean-local: clean-local
 	rm -rf vendor gen Cargo.lock
 
-endif
-
 check:
 	CARGO_HOME="$(CARGO_HOME)" @rustup_home@ \
 		CARGO_TARGET_DIR="$(abs_top_builddir)/rust/target" \
@@ -76,6 +60,11 @@ else
 vendor:
 endif
 
-gen-headers: FORCE
-	cbindgen --config cbindgen.toml --output "gen/rust-bindings.h" > /dev/null
-FORCE:
+# Can only include the headers if we have Python to generate them.
+if HAVE_CBINDGEN
+gen/rust-bindings.h:
+	cbindgen --config $(abs_top_srcdir)/rust/cbindgen.toml \
+		--quiet --output $(abs_top_builddir)/rust/gen/rust-bindings.h
+else
+gen/rust-bindings.h:
+endif