Add version field to ink! metadata (#1313)

* Add `version` field to `InkProject`

* Use `InkProject` directly in metadata codegen

* Remove old metadata versions from version enum

These versions can't be constructed using this version of the crate
anyways, so it doesn't really make sense to keep them.

* Manually implement `Default`

We should change to using the derive macros once
our CI's nightly compiler version gets updated.

* Add metadata `V4` version option

* Use my branch of `cargo-contract` in CI

* Remove deprecated `V3` metadata

We're never able to construct this variant with this
crate anymore, so it doesn't make sense to keep it.

.gitlab-ci.yml

@@ -339,6 +339,7 @@ examples-contract-build:
   <<:                              *docker-env
   <<:                              *test-refs
   script:
+    - cargo install --git /~https://github.com/paritytech/cargo-contract.git --branch hc-versioned-metadata --force
     - cargo contract -V
     - for example in examples/*/; do
         if [ "$example" = "examples/upgradeable-contracts/" ]; then continue; fi;

crates/lang/codegen/src/generator/metadata.rs

@@ -45,10 +45,8 @@ impl GenerateCode for Metadata<'_> {
             #[cfg(not(feature = "ink-as-dependency"))]
             const _: () = {
                 #[no_mangle]
-                pub fn __ink_generate_metadata() -> ::ink_metadata::MetadataVersioned  {
-                    <::ink_metadata::InkProject as ::core::convert::Into<::ink_metadata::MetadataVersioned>>::into(
-                        ::ink_metadata::InkProject::new(#layout, #contract)
-                    )
+                pub fn __ink_generate_metadata() -> ::ink_metadata::InkProject  {
+                    ::ink_metadata::InkProject::new(#layout, #contract)
                 }
             };
         }

crates/metadata/src/lib.rs

@@ -57,38 +57,32 @@ use serde::{
     Serialize,
 };
 
-/// Versioned ink! project metadata.
+/// The metadata version of the generated ink! contract.
+///
+/// The serialized metadata format (which this represents) is different from the
+/// version of this crate or the contract for Rust semantic versioning purposes.
 ///
 /// # Note
 ///
-/// Represents the version of the serialized metadata *format*, which is distinct from the version
-/// of this crate for Rust semantic versioning compatibility.
+/// Versions other than the `Default` are considered deprecated. If you want to
+/// deserialize legacy metadata versions you will need to use an old version of
+/// this crate.
 #[derive(Debug, Serialize, Deserialize)]
-#[allow(clippy::large_enum_variant)]
-pub enum MetadataVersioned {
-    /// Version 0 placeholder. Represents the original non-versioned metadata format.
-    V0(MetadataVersionDeprecated),
-    /// Version 1 of the contract metadata.
-    V1(MetadataVersionDeprecated),
-    /// Version 2 of the contract metadata.
-    V2(MetadataVersionDeprecated),
-    /// Version 3 of the contract metadata.
-    V3(InkProject),
+pub enum MetadataVersion {
+    #[serde(rename = "4")]
+    V4,
 }
 
-impl From<InkProject> for MetadataVersioned {
-    fn from(ink_project: InkProject) -> Self {
-        MetadataVersioned::V3(ink_project)
+impl Default for MetadataVersion {
+    fn default() -> Self {
+        Self::V4
     }
 }
 
-/// Enum to represent a deprecated metadata version that cannot be instantiated.
-#[derive(Debug, Serialize, Deserialize)]
-pub enum MetadataVersionDeprecated {}
-
 /// An entire ink! project for metadata file generation purposes.
 #[derive(Debug, Serialize, Deserialize)]
 pub struct InkProject {
+    version: MetadataVersion,
     #[serde(flatten)]
     registry: PortableRegistry,
     #[serde(rename = "storage")]
@@ -107,6 +101,7 @@ impl InkProject {
         let mut registry = Registry::new();
 
         Self {
+            version: Default::default(),
             layout: layout.into().into_portable(&mut registry),
             spec: spec.into().into_portable(&mut registry),
             registry: registry.into(),