Improve error reporting in build failures because of missing environment variables

Author: NlightNFotis

src/libcprover-rust/build.rs

@@ -8,17 +8,20 @@ fn get_current_working_dir() -> std::io::Result<PathBuf> {
     env::current_dir()
 }
 
-fn get_lib_directory() -> Result<String, VarError> {
-    env::var("CBMC_LIB_DIR")
-}
-
 // Passed by the top-level CMakeLists.txt to control which version of the
 // static library of CBMC we're linking against. A user can also change the
 // environment variable to link against different versions of CBMC.
 fn get_cbmc_version() -> Result<String, VarError> {
     env::var("CBMC_VERSION")
 }
 
+// Passed by the top-level CMakeLists.txt to control where the static library we
+// link against is located. A user can also change the location of the library
+// on their system by supplying the environment variable themselves.
+fn get_lib_directory() -> Result<String, VarError> {
+    env::var("CBMC_LIB_DIR")
+}
+
 fn get_library_build_dir() -> std::io::Result<PathBuf> {
     let env_var_fetch_result = get_lib_directory();
     if let Ok(build_dir) = env_var_fetch_result {
@@ -28,7 +31,7 @@ fn get_library_build_dir() -> std::io::Result<PathBuf> {
     }
     Err(Error::new(
         ErrorKind::Other,
-        "Please set the environment variable CBMC_LIB_DIR with the path that contains the libcprover.x.y.z.a library on your system",
+        "Environment variable `CBMC_LIB_DIR' not set",
     ))
 }
 
@@ -48,7 +51,14 @@ fn main() {
 
     let libraries_path = match get_library_build_dir() {
         Ok(path) => path,
-        Err(err) => panic!("Error: {}", err),
+        Err(err) => {
+            let error_message = &format!(
+                "Error: {}.\n Advice: {}.",
+                err,
+                "Please set the environment variable `CBMC_LIB_DIR' with the path that contains libcprover.x.y.z.a on your system"
+            );
+            panic!("{}", error_message);
+        }
     };
 
     println!(
@@ -58,7 +68,14 @@ fn main() {
 
     let cprover_static_libname = match get_cbmc_version() {
         Ok(version) => String::from("cprover.") + &version,
-        Err(err) => panic!("Error: {}", err),
+        Err(_) => {
+            let error_message = &format!(
+                "Error: {}.\n Advice: {}.",
+                "Environment variable `CBMC_VERSION' not set",
+                "Please set the environment variable `CBMC_VERSION' with the version of CBMC you want to link against (e.g. 5.78.0)"
+            );
+            panic!("{}", error_message);
+        }
     };
 
     println!("cargo:rustc-link-lib=static={}", cprover_static_libname);