[PATCH 3/6] kbuild: rust: re-run Kconfig if the version text changes

[Miguel Ojeda <ojeda@kernel.org>]

Re-run Kconfig if we detect the Rust compiler has changed via the version
text, like it is done for C.

Unlike C, and unlike `RUSTC_VERSION`, the `RUSTC_VERSION_TEXT` is kept
under `depends on RUST`, since it should not be needed unless `RUST`
is enabled.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
Masahiro: I think leaving the `depends on RUST` in `RUSTC_VERSION` is
OK, but since this is different from the C side, please let me know if
you prefer otherwise. Thanks!

 Makefile     | 5 +++--
 init/Kconfig | 4 +++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 8ad55d6e7b60..2b5f9f098b6f 100644
--- a/Makefile
+++ b/Makefile
@@ -648,9 +648,10 @@ endif

 # The expansion should be delayed until arch/$(SRCARCH)/Makefile is included.
 # Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile.
-# CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
+# CC_VERSION_TEXT and RUSTC_VERSION_TEXT are referenced from Kconfig (so they need export),
 # and from include/config/auto.conf.cmd to detect the compiler upgrade.
 CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
+RUSTC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(RUSTC) --version 2>/dev/null | head -n 1))

 ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 include $(srctree)/scripts/Makefile.clang
@@ -671,7 +672,7 @@ ifdef config-build
 # KBUILD_DEFCONFIG may point out an alternative default configuration
 # used for 'make defconfig'
 include $(srctree)/arch/$(SRCARCH)/Makefile
-export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT
+export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT RUSTC_VERSION_TEXT

 config: outputmakefile scripts_basic FORCE
 	$(Q)$(MAKE) $(build)=scripts/kconfig $@
diff --git a/init/Kconfig b/init/Kconfig
index 2f974f412374..b0238c4b6e79 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1926,7 +1926,9 @@ config RUST
 config RUSTC_VERSION_TEXT
 	string
 	depends on RUST
-	default "$(shell,LC_ALL=C $(RUSTC) --version 2>/dev/null | head -n 1)"
+	default "$(RUSTC_VERSION_TEXT)"
+	help
+	  See `CC_VERSION_TEXT`.

 config BINDGEN_VERSION_TEXT
 	string
--
2.46.0