have prepare add a generic PrepareError context

if a more specifc one hasn't already been provided

this way we can easily distinguish BuildDirectory::run failing due to Prepare::prepare failing from it failing for other reasons

Author: Skgland

src/build.rs

@@ -1,6 +1,6 @@
 use crate::cmd::{Command, MountKind, Runnable, SandboxBuilder};
 use crate::prepare::Prepare;
-use crate::{Crate, Toolchain, Workspace};
+use crate::{Crate, PrepareError, Toolchain, Workspace};
 use std::path::PathBuf;
 use std::vec::Vec;
 
@@ -194,7 +194,13 @@ impl BuildDirectory {
         }
 
         let mut prepare = Prepare::new(&self.workspace, toolchain, krate, &source_dir, patches);
-        prepare.prepare()?;
+        prepare.prepare().map_err(|err| {
+            if err.downcast_ref::<PrepareError>().is_none() {
+                err.context(PrepareError::Unknown)
+            } else {
+                err
+            }
+        })?;
 
         std::fs::create_dir_all(self.target_dir())?;
         let res = f(&Build {

src/prepare.rs

@@ -390,6 +390,8 @@ pub enum PrepareError {
     /// Some of the dependencies do not exist anymore.
     #[error("the crate depends on missing dependencies: \n\n{0}")]
     MissingDependencies(String),
+    #[error("prepare failed without further details")]
+    Unknown,
 }
 
 #[cfg(test)]

tests/buildtest/runner.rs

@@ -63,29 +63,6 @@ impl Runner {
     }
 }
 
-macro_rules! test_prepare_unknown_err {
-    ($name:ident, $krate:expr, $expected:ident $(,$expected_output:expr)?) => {
-        #[test]
-        fn $name() {
-            runner::run($krate, |run| {
-                let res = run.run(
-                    rustwide::cmd::SandboxBuilder::new().enable_networking(false),
-                    |_| Ok(()),
-                );
-                if let Some(err) = res
-                    .err()
-                    .and_then(|err| err.downcast::<rustwide::PrepareError>().ok())
-                {
-                    panic!("did get an unexpected error: \n\n{}", err);
-                } else {
-                    // Everything is OK!
-                }
-                Ok(())
-            });
-        }
-    };
-}
-
 macro_rules! test_prepare_error {
     ($name:ident, $krate:expr, $expected:ident) => {
         #[test]
@@ -119,6 +96,8 @@ macro_rules! test_prepare_error {
     };
 }
 
+pub(crate) use test_prepare_error;
+
 macro_rules! test_prepare_error_stderr {
     ($name:ident, $krate:expr, $expected:ident, $expected_output:expr) => {
         #[test]
@@ -151,3 +130,9 @@ macro_rules! test_prepare_error_stderr {
         }
     };
 }
+
+macro_rules! test_prepare_unknown_err {
+    ($name:ident, $krate:expr, $expected:ident $(,$expected_output:expr)?) => {
+        $crate::buildtest::runner::test_prepare_error!($name, $krate, Unknown);
+    };
+}