Remove requirement on bitvec for std feature and constructing TypeDef…

…BitSequence. (#168)

* Don't force bitvec to be included when "std" is enabled.

* update UI test output

* Ah, we test on nightly

* don't require bit-vec to construct a TypeDefBitSequence

* no bit-vec feature on std actually

* update test output again

* bump rust-version to 1.60.0 and add section in unreleased

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- Minimum Rust version is 1.60.0 owing to using weak dependency crate features.
+- Loosen restriction on `TypeDefBitSequence::new()` so that `bitvec` isn't required, and try to avoid pulling in `bitvec` when the `std` feature is enabled [(#168)](https://github.com/paritytech/scale-info/pull/168)
+
 ## [2.1.2] - 2022-05-18
 
 ### Fixed

Cargo.toml

@@ -3,7 +3,7 @@ name = "scale-info"
 version = "2.1.2"
 authors = ["Parity Technologies <admin@parity.io>"]
 edition = "2021"
-rust-version = "1.56.1"
+rust-version = "1.60.0"
 
 license = "Apache-2.0"
 readme = "README.md"
@@ -25,7 +25,7 @@ scale = { package = "parity-scale-codec", version = "3", default-features = fals
 [features]
 default = ["std"]
 std = [
-    "bitvec/std",
+    "bitvec?/std",
     "scale/std",
 ]
 derive = [

src/ty/mod.rs

@@ -576,17 +576,21 @@ where
     }
 }
 
-#[cfg(feature = "bit-vec")]
 impl TypeDefBitSequence {
     /// Creates a new [`TypeDefBitSequence`] for the supplied bit order and bit store types.
-    pub fn new<T, O>() -> Self
+    ///
+    /// With the `bit-vec` feature enabled, the expected usage is to provide either
+    /// `bitvec::order::Lsb0` or `bitvec::order::Msb0` as the order type, and then something
+    /// like u8, u8, or u32 as the store type. Without the `bit-vec` feature enabled, it's
+    /// recommended that your types have identical `TypeInfo` to those.
+    pub fn new<Store, Order>() -> Self
     where
-        T: bitvec::store::BitStore + TypeInfo + 'static,
-        O: bitvec::order::BitOrder + TypeInfo + 'static,
+        Store: TypeInfo + 'static,
+        Order: TypeInfo + 'static,
     {
         Self {
-            bit_store_type: MetaType::new::<T>(),
-            bit_order_type: MetaType::new::<O>(),
+            bit_store_type: MetaType::new::<Store>(),
+            bit_order_type: MetaType::new::<Order>(),
         }
     }
 }

test_suite/tests/ui/fail_missing_derive.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `PawType<u16>: TypeInfo` is not satisfied
-  --> tests/ui/fail_missing_derive.rs:19:5
+  --> tests/ui/fail_missing_derive.rs:19:24
    |
 19 |     assert_type_info::<Cat<bool, u8, u16>>();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `TypeInfo` is not implemented for `PawType<u16>`
+   |                        ^^^^^^^^^^^^^^^^^^ the trait `TypeInfo` is not implemented for `PawType<u16>`
    |
    = help: the following other types implement trait `TypeInfo`:
              &T
@@ -14,7 +14,7 @@ error[E0277]: the trait bound `PawType<u16>: TypeInfo` is not satisfied
              (A, B, C, D, E)
              (A, B, C, D, E, F)
            and 54 others
-note: required because of the requirements on the impl of `TypeInfo` for `Cat<bool, u8, u16>`
+note: required for `Cat<bool, u8, u16>` to implement `TypeInfo`
   --> tests/ui/fail_missing_derive.rs:8:10
    |
 8  | #[derive(TypeInfo)]