Re: [PATCH v2 1/2] rust: pick a GCC-compatible Cargo target under MSYS2/MinGW

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Junio & James,

On Fri, 11 Sep 2026, James Le Cuirot wrote:

> On Fri, 2026-09-11 at 14:09 -0700, Junio C Hamano wrote:
> > "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
> > writes:
> > 
> > > @@ -993,6 +993,7 @@ endif
> > >  ifndef DEBUG
> > >  CARGO_ARGS += --release
> > >  endif
> > > +CARGO_ARGS += $(if $(CARGO_TARGET),--target $(CARGO_TARGET))
> > 
> > Should this use CARGO_BUILD_TARGET (instead of CARGO_TARGET) to
> > match what the officially supported Cargo environment variable is
> > called?  It would also help us work better with the changes from the
> > jc/rust-cargo-build-target topic.

Sure.

> > 
> > Thanks.
> 
> Yes, without explicitly setting --target at all.

Cool! My first experiment failed because I missed that Makefile does not
automatically export `CARGO_BUILD_TARGET`... 🤦 But now that I explicitly
export it, it works as you claimed it would.

Thank you!
Johannes

> This is how Gentoo Linux supports cross-compiling of its Rust packages.
> Just avoid setting CARGO_BUILD_TARGET (or passing --target) when you're
> not cross-compiling. It will cause Cargo to behave differently, even if
> you give the native tuple. For example, RUSTFLAGS is normally applied to
> both the build host binaries and the target host binaries, but when an
> explicit target is set, RUSTFLAGS is only applied to the target host
> binaries.
> 
> Regards,
> Chewi
> 
> > Author: James Le Cuirot <chewi@gentoo.org>
> > Date:   Thu Sep 10 11:20:14 2026 +0100
> > 
> >     rust: respect CARGO_BUILD_TARGET when locating build output
> >     
> >     When cross-compiling, Cargo always writes to a target-tuple subdirectory
> >     determined by CARGO_BUILD_TARGET, even when it matches the native tuple.
> >     The build looked in $BUILD_DIR/$BUILD_TYPE directly, so it failed to
> >     locate the freshly built library.
> >     
> >     Respect CARGO_BUILD_TARGET in the output path so the correct artifact
> >     is located.
> >     
> >     Signed-off-by: James Le Cuirot <chewi@gentoo.org>
> >     Signed-off-by: Junio C Hamano <gitster@pobox.com>
> > 
> > diff --git a/Makefile b/Makefile
> > index d4b775953d..f0ca2e4f72 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -959,7 +959,7 @@ RUST_LIB_NAME = gitcore.lib
> >  else
> >  RUST_LIB_NAME = libgitcore.a
> >  endif
> > -RUST_LIB = target/$(RUST_BUILD_CONFIG)/$(RUST_LIB_NAME)
> > +RUST_LIB = target/$(if $(CARGO_BUILD_TARGET),$(CARGO_BUILD_TARGET)/)$(RUST_BUILD_CONFIG)/$(RUST_LIB_NAME)
> >  endif
> >  
> >  GITLIBS = common-main.o $(LIB_FILE)
> > diff --git a/src/cargo-meson.sh b/src/cargo-meson.sh
> > index 75f3cd1265..83c7e7b79b 100755
> > --- a/src/cargo-meson.sh
> > +++ b/src/cargo-meson.sh
> > @@ -38,7 +38,7 @@ then
> >  	exit $RET
> >  fi
> >  
> > -if ! cmp "$BUILD_DIR/$BUILD_TYPE/$LIBNAME" "$BUILD_DIR/libgitcore.a" >/dev/null 2>&1
> > +if ! cmp "$BUILD_DIR/${CARGO_BUILD_TARGET:+$CARGO_BUILD_TARGET/}$BUILD_TYPE/$LIBNAME" "$BUILD_DIR/libgitcore.a" >/dev/null 2>&1
> >  then
> > -	cp "$BUILD_DIR/$BUILD_TYPE/$LIBNAME" "$BUILD_DIR/libgitcore.a"
> > +	cp "$BUILD_DIR/${CARGO_BUILD_TARGET:+$CARGO_BUILD_TARGET/}$BUILD_TYPE/$LIBNAME" "$BUILD_DIR/libgitcore.a"
> >  fi
>