Enable Rust by default

Our breaking changes document says that we'll enable Rust by default in
Git 2.54.  Adjust the Makefile to switch the option from WITH_RUST to
NO_RUST to enable it by default and update the help text accordingly.
Similarly, for Meson, enable the option by default and do not
automatically disable it if Cargo is missing, since the goal is to help
users find where they are likely to have problems in the future.

Update our CI tests to swap out the single Linux job with Rust to a
single job without.  Similarly, update the Windows Makefile job to not
use Rust, while the Meson job (which does not build with ci/lib.sh) will
default to having it enabled.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: bk2204

Makefile

@@ -498,9 +498,9 @@ include shared.mak
 #
 # == Optional Rust support ==
 #
-# Define WITH_RUST if you want to include features and subsystems written in
-# Rust into Git. For now, Rust is still an optional feature of the build
-# process. With Git 3.0 though, Rust will always be enabled.
+# Define NO_RUST if you want to disable features and subsystems written in Rust
+# from being compiled into Git. For now, Rust is still an optional feature of
+# the build process. With Git 3.0 though, Rust will always be enabled.
 #
 # Building Rust code requires Cargo.
 #
@@ -1351,7 +1351,7 @@ LIB_OBJS += urlmatch.o
 LIB_OBJS += usage.o
 LIB_OBJS += userdiff.o
 LIB_OBJS += utf8.o
-ifndef WITH_RUST
+ifdef NO_RUST
 LIB_OBJS += varint.o
 endif
 LIB_OBJS += version.o
@@ -1590,7 +1590,7 @@ endif
 ALL_CFLAGS = $(DEVELOPER_CFLAGS) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_APPEND)
 ALL_LDFLAGS = $(LDFLAGS) $(LDFLAGS_APPEND)
 
-ifdef WITH_RUST
+ifndef NO_RUST
 BASIC_CFLAGS += -DWITH_RUST
 GITLIBS += $(RUST_LIB)
 ifeq ($(uname_S),Windows)

ci/lib.sh

@@ -372,6 +372,9 @@ linux-asan-ubsan)
 osx-meson)
 	MESONFLAGS="$MESONFLAGS -Dcredential_helpers=osxkeychain"
 	;;
+windows-*)
+	export NO_RUST=UnfortunatelyYes
+	;;
 esac
 
 MAKEFLAGS="$MAKEFLAGS CC=${CC:-cc}"

ci/run-build-and-tests.sh

@@ -10,7 +10,6 @@ export TEST_CONTRIB_TOO=yes
 case "$jobname" in
 fedora-breaking-changes-musl|linux-breaking-changes)
 	export WITH_BREAKING_CHANGES=YesPlease
-	export WITH_RUST=YesPlease
 	MESONFLAGS="$MESONFLAGS -Dbreaking_changes=true"
 	MESONFLAGS="$MESONFLAGS -Drust=enabled"
 	;;
@@ -30,6 +29,7 @@ linux-TEST-vars)
 	export GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL=1
 	;;
 linux-clang)
+	export NO_RUST=UnfortunatelyYes
 	export GIT_TEST_DEFAULT_HASH=sha1
 	;;
 linux-sha256)

meson.build

@@ -1746,7 +1746,7 @@ version_def_h = custom_target(
 libgit_sources += version_def_h
 
 cargo = find_program('cargo', dirs: program_path, native: true, required: get_option('rust'))
-rust_option = get_option('rust').disable_auto_if(not cargo.found())
+rust_option = get_option('rust')
 if rust_option.allowed()
   subdir('src')
   libgit_c_args += '-DWITH_RUST'

meson_options.txt

@@ -77,7 +77,7 @@ option('zlib_backend', type: 'combo', choices: ['auto', 'zlib', 'zlib-ng'], valu
 # Build tweaks.
 option('breaking_changes', type: 'boolean', value: false,
   description: 'Enable upcoming breaking changes.')
-option('rust', type: 'feature', value: 'auto',
+option('rust', type: 'feature', value: 'enabled',
   description: 'Enable building with Rust.')
 option('macos_use_homebrew_gettext', type: 'boolean', value: true,
   description: 'Use gettext from Homebrew instead of the slightly-broken system-provided one.')