Error feature flag to tide MSRV concerns for now

Author: clarfonthey

Cargo.toml

@@ -37,7 +37,7 @@ exclude = ["target/*", "Cargo.lock", "scripts/tmp", "*.txt", "tests/*"]
 version = "1"
 features = ["alloc"]
 
-
 [features]
 default = ["std"]
-std = []
+std = ["error"]
+error = []

src/quick_check.rs

@@ -3,7 +3,11 @@ use crate::stream_safe;
 use crate::tables;
 use crate::UnicodeNormalization;
 
+#[cfg(all(feature = "error", not(feature = "std")))]
 use core::error::Error;
+#[cfg(feature = "std")]
+use std::error::Error;
+
 use core::fmt;
 
 /// Error returned when a string is not properly normalized.
@@ -27,6 +31,7 @@ impl fmt::Display for NormalizationError {
         )
     }
 }
+#[cfg(feature = "error")]
 impl Error for NormalizationError {}
 
 /// Whether additional checking is necessary to verify normalization.