Add borrowed Ref variants of types

[leighmcculloch]

Note

Part of a stack of PRs that must merge in this order.

A first group of PRs change contract specs so that they are produced at compile time instead of at proc-macro execution time. This provides the foundation to construct the specs from information that is only known at compile time, like the fully qualified name of a type:

1. Add borrowed Ref variants of types #560 ← this PR
2. Add const XDR serialization #562
3. Encode contract spec XDR at compile time rs-soroban-sdk#1965

A second group of PRs changes the type names that the sdk stores in specs are fully qualified type names, and then the cli reduces them down to unique simple identifiers. During the contract build the types are given names like ::mycrate::mymod::MyType instead of MyType. Then the cli reduces them back down to simple names after spec shaking. Qualified type names make it possible to uniquely identify types in the spec, even when they have the same name. This resolves several problems with contract specs the type identify problem (stellar/rs-soroban-sdk#1570), type aliases limitations (stellar/rs-soroban-sdk#1857 stellar/rs-soroban-sdk#1063), and optimise spec shaking data section size (stellar/rs-soroban-sdk#1978):

1. Widen contract spec type and event name limits stellar-xdr#312
2. Widen contract spec type and event name limits #566
3. Qualify type and event names rs-soroban-sdk#1970
4. Reduce qualified type and event names stellar-cli#2674

Note that downstream clients and SDKs should see no, or little, change because the cli will during the build process reduce the fully qualified names back to simple unique names. Contracts that had colliding type names, which meant they could not be used with clients, will now work.

A third group of PRs are an optimisation to spec shaking v2, and will use the new unique type names to shake type specs by reachability, producing a dependency graph (thanks @mootz12), so that only spec entries that can't be reached from fns, like errors and events, get spec markers from dead-code-elimination:

1. Shake specs by reachability and markers rs-soroban-sdk#2043
2. Shake by the recorded version stellar-cli#2720

What

Add a borrowing {Type}Ref<'a> counterpart for every generated type that directly or transitively contains heap data.

Why

The owned types require heap allocation to construct, so XDR values can't be built from borrowed slices or inside const contexts.

Known limitations

View types encode via WriteXdr/to_xdr but cannot implement ReadXdr/from_xdr (decoding must target the owned types), and they have no serde support.

[Copilot]

Pull request overview

Adds allocation-free borrowed Ref counterparts for heap-backed generated XDR types.

Changes:

• Adds borrowed container types, conversion support, and XDR encoding.
• Extends generator analysis/templates to emit borrowed variants.
• Regenerates XDR output and adds integration tests.

Reviewed changes

Copilot reviewed 1 out of 484 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/generated.rs	Adds shared borrowed-type infrastructure.
src/generated/*.rs	Regenerates affected XDR types with Ref or IntoOwned implementations.
tests/common/mod.rs	Provides representative owned and borrowed fixtures.
tests/ref_types.rs	Tests construction, limits, conversion, and encoding.
xdr-generator-rust/generator/header.rs	Defines borrowed containers and conversion support.
xdr-generator-rust/generator/src/generator.rs	Analyzes which types require borrowed variants.
xdr-generator-rust/generator/src/output.rs	Adds borrowed-type template metadata.
xdr-generator-rust/generator/src/tests/generator.rs	Tests generator borrow analysis.
xdr-generator-rust/generator/src/types.rs	Resolves borrowed and cyclic field types.
xdr-generator-rust/generator/templates/enum.rs.jinja	Emits identity conversions for enums.
xdr-generator-rust/generator/templates/into_owned.rs.jinja	Adds reusable identity conversion generation.
xdr-generator-rust/generator/templates/struct.rs.jinja	Emits borrowed structs and conversions.
xdr-generator-rust/generator/templates/typedef_newtype.rs.jinja	Emits borrowed newtypes and conversions.
xdr-generator-rust/generator/templates/union.rs.jinja	Emits borrowed unions and cyclic conversions.

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[leighmcculloch]

This gap is pretty narrow and won't break compilation. I think we should defer to look at this if we ever need it.