Merge pull request #7495 from NlightNFotis/make_rust_build_opt

Change default build to *not* include Rust API.

Author: NlightNFotis

CMakeLists.txt

@@ -256,10 +256,10 @@ if(WITH_JBMC)
     add_subdirectory(jbmc)
 endif()
 
-option(WITH_RUST_API "Build with the CPROVER Rust API" ON)
-if(${CMAKE_VERSION} VERSION_LESS "3.19.0")
+option(WITH_RUST_API "Build with the CPROVER Rust API" OFF)
+if(${CMAKE_VERSION} VERSION_LESS "3.19.0" AND WITH_RUST_API)
     message("Unable to build the Rust API without version CMake 3.19.0")
-    message("(The Rust build depends on CMake plugins with dependencies on CMake 3.19.0 and above)")
+    message(FATAL_ERROR "(The Rust build depends on CMake plugins with dependencies on CMake 3.19.0 and above)")
 else()
     if(WITH_RUST_API)
     include(FetchContent)

COMPILING.md

@@ -562,3 +562,31 @@ then run make as follows.
 cd unit
 make test
 ```
+
+## Rust API
+
+CBMC is now offering a [Rust API](src/libcprover-rust/). To build that along with
+CBMC, you need two things:
+
+- Rust/Cargo, instructions the installation of which can be found [here](https://www.rust-lang.org/tools/install), and
+- CMake (the Rust API doesn't support being built with `Make` yet)
+  - Version `3.19.0`+ is required for the build, because of a dependency on CMake modules
+    that need the higher version themselves.
+
+Provided these two are available, you can perform a CBMC build *including*
+the Rust API by passing in the option `WITH_RUST_API` to `CMake` like this:
+
+```sh
+$ cmake -S. -Bbuild -DWITH_RUST_API=ON <other_options>
+[...]
+-- Rust Target: aarch64-apple-darwin
+-- Found Rust: /opt/homebrew/bin/rustc (found version "1.66.1") 
+-- Using Corrosion as a subdirectory
+-- Configuring done
+-- Generating done
+-- Build files have been written to: cbmc/build
+```
+
+If you come across any issues during the configuration or the build of the Rust API,
+please let us know by filing a [bug report](https://github.com/diffblue/cbmc/issues/new)
+and mark it with the label `Rust API` if possible.