Add environment variable for include folder in build and update build docs

Author: NlightNFotis

src/libcprover-rust/build.rs

@@ -1,7 +1,6 @@
 use std::env;
 use std::env::VarError;
 use std::io::{Error, ErrorKind};
-use std::path::Path;
 use std::path::PathBuf;
 
 fn get_current_working_dir() -> std::io::Result<PathBuf> {
@@ -37,12 +36,40 @@ fn get_library_build_dir() -> std::io::Result<PathBuf> {
     ))
 }
 
+// This is needed so that cargo can find the include folder for the C++
+// API headers at compile time.
+fn get_include_directory_envvar() -> Result<String, VarError> {
+    env::var("CBMC_INCLUDE_DIR")
+}
+
+fn get_include_directory() -> std::io::Result<PathBuf> {
+    let env_var_fetch_result = get_include_directory_envvar();
+    if let Ok(build_dir) = env_var_fetch_result {
+        let mut path = PathBuf::new();
+        path.push(build_dir);
+        return Ok(path);
+    }
+    Err(Error::new(
+        ErrorKind::Other,
+        "Environment variable `CBMC_INCLUDE_DIR' not set",
+    ))
+}
+
 fn main() {
-    let cbmc_source_path = Path::new("..");
-    let cpp_api_path = Path::new("../libcprover-cpp/");
+    let cpp_api_include_path = match get_include_directory() {
+        Ok(path) => path,
+        Err(err) => {
+            let error_message = &format!(
+                "Error: {}.\n Advice: {}.",
+                err,
+                "Please set the environment variable `CBMC_INCLUDE_DIR' with the path that contains cprover/api.h on your system"
+            );
+            panic!("{}", error_message);
+        }
+    };
+
     let _build = cxx_build::bridge("src/lib.rs")
-        .include(cbmc_source_path)
-        .include(cpp_api_path)
+        .include(cpp_api_include_path)
         .include(get_current_working_dir().unwrap())
         .file("src/c_api.cc")
         .flag_if_supported("-std=c++11")

src/libcprover-rust/readme.md

@@ -15,7 +15,9 @@ project:
 
 * `CBMC_LIB_DIR`, for selecting where the `libcprover-x.y.z.a` is located
   (say, if you have downloaded a pre-packaged release which contains
-   the static library), and
+   the static library),
+* `CBMC_INCLUDE_DIR`, for selecting where the `cprover/api.h` is located,
+  and
 * `CBMC_VERSION`, for selecting the version of the library to link against
   (this is useful if you have multiple versions of the library in the same
    location and you want to control which version you compile against).
@@ -27,7 +29,7 @@ directory of the CBMC project.)
 ```sh
 $ cd src/libcprover-rust
 $ cargo clean
-$ CBMC_LIB_DIR=../../build/lib CBMC_VERSION=5.78.0 cargo build
+$ CBMC_INCLUDE_DIR=../../build/include CBMC_LIB_DIR=../../build/lib CBMC_VERSION=5.78.0 cargo build
 ```
 
 To build the project and run its associated tests, the command sequence would
@@ -36,7 +38,7 @@ look like this:
 ```sh
 $ cd src/libcprover-rust
 $ cargo clean
-$ CBMC_LIB_DIR=../../build/lib CBMC_VERSION=5.78.0 cargo test -- --test-threads=1 --nocapture
+$ CBMC_INCLUDE_DIR=../../build/include CBMC_LIB_DIR=../../build/lib CBMC_VERSION=5.78.0 cargo test -- --test-threads=1 --nocapture
 ```
 
 ## Notes