Fix no_std_example

Cargo.toml

@@ -7,5 +7,16 @@ members = [
     "nutype_macros",
     "test_suite",
     "dummy",
-    "examples/*",
+
+    # All examples except "no_std_example" are tested in the test suite
+    "examples/any_arbitrary",
+    "examples/float_arbitrary",
+    "examples/float_sortable",
+    "examples/integer_arbitrary",
+    "examples/integer_bounded",
+    "examples/new_unchecked_example",
+    # "examples/no_std_example",
+    "examples/serde_complex",
+    "examples/string_bounded_len",
+    "examples/string_regex_email",
 ]

examples/no_std_example/Cargo.toml

@@ -7,3 +7,6 @@ edition = "2021"
 
 [dependencies]
 nutype = { path = "../../nutype", default-features = false }
+
+# Exclude this package from the common workspace, since it's no_std.
+[workspace]

examples/no_std_example/src/main.rs

@@ -1,3 +1,5 @@
+// This example exists to ensure that code generated by nutype macro
+// can compile in no_std environment.
 #![no_main]
 #![no_std]
 
@@ -9,5 +11,64 @@ fn panic(_panic: &PanicInfo<'_>) -> ! {
     loop {}
 }
 
-#[nutype(validate(greater_or_equal = 1, less_or_equal = 6), derive(Debug))]
+// Integer
+#[nutype(
+    validate(greater_or_equal = 1, less_or_equal = 6),
+    sanitize(with = |x| x),
+    derive(
+        Debug,
+        Clone,
+        PartialEq,
+        Eq,
+        PartialOrd,
+        Ord,
+        FromStr,
+        AsRef,
+        Deref,
+        TryFrom,
+        Into,
+        Hash,
+        Borrow,
+        Display,
+        Default,
+    ),
+    default = 4
+)]
 struct GermanTaxClass(i64);
+
+// Float
+#[nutype(
+    validate(greater_or_equal = 0.0, less_or_equal = 1024.0, finite),
+    sanitize(with = |x| x),
+    derive(
+        Debug,
+        Clone,
+        PartialEq,
+        Eq,
+        PartialOrd,
+        Ord,
+        FromStr,
+        AsRef,
+        Deref,
+        TryFrom,
+        Into,
+        Borrow,
+        Display,
+        Default,
+    ),
+    default = 0.0
+)]
+struct Width(f64);
+
+// NOTE: strings are not working yet with no_std
+
+// Any other type
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Point {
+    x: i32,
+    y: i32,
+}
+#[nutype(derive(
+    Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, AsRef, Into, From, Deref, Borrow, Hash
+))]
+pub struct Location(Point);

nutype_macros/src/common/gen/parse_error.rs

@@ -1,3 +1,4 @@
+use cfg_if::cfg_if;
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
 
@@ -55,11 +56,19 @@ pub fn gen_def_parse_error(
         }
     };
 
-    let impl_std_error = quote! {
-        impl ::std::error::Error for #parse_error_type_name {
-            fn source(&self) -> Option<&(dyn ::std::error::Error + 'static)> {
-                None
-            }
+    cfg_if! {
+        if #[cfg(feature = "std")] {
+            let impl_std_error = quote! {
+                impl ::std::error::Error for #parse_error_type_name {
+                    fn source(&self) -> Option<&(dyn ::std::error::Error + 'static)> {
+                        None
+                    }
+                }
+            };
+        } else {
+            // NOTE: There is no `::core::error::Error` yet in stable Rust.
+            // So for `no_std` we just don't implement `Error` trait.
+            let impl_std_error = quote! {};
         }
     };