errors: hide internal error types from ErrorKind

As we plan to export ErrorKind, these kinds of internal errors should be
made opaque since it seems incredibly unlikely that any real users would
ever need to check them.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

src/error.rs

@@ -108,8 +108,7 @@ pub(crate) enum ErrorKind {
     NotSupported,
     InvalidArgument,
     SafetyViolation,
-    BadSymlinkStack,
-    ParseError,
+    InternalError,
     // TODO: We might want to use Option<std::io::ErrorKind>?
     OsError(Option<i32>),
 }
@@ -121,12 +120,16 @@ impl ErrorImpl {
             Self::NotSupported { .. } => ErrorKind::NotSupported,
             Self::InvalidArgument { .. } => ErrorKind::InvalidArgument,
             Self::SafetyViolation { .. } => ErrorKind::SafetyViolation,
-            Self::BadSymlinkStackError { .. } => ErrorKind::BadSymlinkStack,
-            Self::ParseIntError(_) => ErrorKind::ParseError,
+            // Any syscall-related errors get mapped to an OsError, since the
+            // distinction doesn't matter to users checking error values.
             Self::OsError { source, .. } => ErrorKind::OsError(source.raw_os_error()),
             Self::RawOsError { source, .. } => {
                 ErrorKind::OsError(source.root_cause().raw_os_error())
             }
+            // These errors are internal error types that we don't want to
+            // expose outside of the crate. All that matters to users is that
+            // there was some internal error.
+            Self::BadSymlinkStackError { .. } | Self::ParseIntError(_) => ErrorKind::InternalError,
             Self::Wrapped { source, .. } => source.kind(),
         }
     }

src/tests/capi/utils.rs

@@ -72,7 +72,7 @@ impl ErrorImpl for CapiError {
             // TODO: We should probably have an actual "no-op" error here that
             //       is unused except for these tests so we can properly detect
             //       a bad ErrorKind.
-            ErrorKind::ParseError
+            ErrorKind::InternalError
         }
     }
 }

src/utils/sysctl.rs

@@ -114,7 +114,7 @@ mod tests {
             super::sysctl_read_parse::<u32>(&GLOBAL_PROCFS_HANDLE, "kernel.printk")
                 .as_ref()
                 .map_err(Error::kind),
-            Err(ErrorKind::ParseError),
+            Err(ErrorKind::InternalError),
             "parsing line from multi-number sysctl",
         );
     }
@@ -126,7 +126,7 @@ mod tests {
             super::sysctl_read_parse::<u32>(&GLOBAL_PROCFS_HANDLE, "kernel.random.uuid")
                 .as_ref()
                 .map_err(Error::kind),
-            Err(ErrorKind::ParseError),
+            Err(ErrorKind::InternalError),
             "parsing line from non-number sysctl",
         );
     }