fix(lang/syn): migrate anchor-syn and proc-macro crates to syn 2.0

[eteen12]

Summary

Fixes #4521.

Upgrades syn from 1.x to 2.0 across anchor-syn and all dependent proc-macro crates:

• lang/attribute/{program,account,access-control,error,event,constant}
• lang/derive/{accounts,serde,space}

Key syn 2.0 breaking changes addressed

syn 1.x	syn 2.x
attr.path (field)	attr.path() (method)
attr.tokens (field)	attr.meta / MetaList::tokens
NestedMeta	syn::Meta
parse_meta()	attr.meta
LifetimeDef	LifetimeParam
Expr::Type	FnArg::Typed
ParseMacroInput	Parse
parse_terminated(f)	parse_terminated(f, Token![,])

Removes the silent-fail bandaid from #4520

CrateContext::parse now hard-fails with an error message when it cannot parse the crate, rather than silently producing an incomplete IDL. This was only safe to remove because syn 2.0 can parse modern Rust syntax (e.g. impl Clone + use<T> precise-capture bounds from Rust 1.82+) that syn 1.x could not.

Regression test

Adds tests/idl-forward-ref — a minimal Anchor program that uses + use<T> precise-capture syntax. Building it with --features idl-build previously triggered the silent-fail path; it now compiles and generates correct IDL.

Test plan

• cargo check -p anchor-syn — no errors
• cargo check -p idl-forward-ref --features idl-build — no errors
• cargo check -p anchor-attribute-{program,account,access-control,error,event,constant} -p anchor-derive-{accounts,serde,space} — no errors

[vercel]

@eteen12 is attempting to deploy a commit to the Solana Foundation Team on Vercel.

A member of the Team first needs to authorize it.

[greptile-apps]

Greptile Summary

This PR migrates anchor-syn and all dependent proc-macro crates from syn 1.x to 2.0, replacing deprecated API surface (attr.path field → attr.path() method, NestedMeta → syn::Meta, LifetimeDef → LifetimeParam, Expr::Type → FnArg::Typed, etc.) and removing the silent-fail bandaid from #4520 now that syn 2.0 can parse modern Rust syntax like precise-capture + use<T> bounds.

• All syn 2.0 API migrations are mechanically correct; parse_terminated calls now pass the separator token as required, and attr.tokens accesses are properly replaced with attr.meta pattern matches.
• CrateContext::parse now hard-fails (and caches the error) instead of silently producing an incomplete IDL, which is intentional and safe with syn 2.0.
• A new regression-test crate (idl-forward-ref) proves the + use<T> parse path no longer fails.

Confidence Score: 4/5

The migration is mechanically correct throughout; the one concern worth resolving before merging is the removal of the Spanned trait impl from Context.

Every syn 2.0 API substitution looks correct. The Spanned trait impl removal from Context in anchor-syn (a published crate) will silently break downstream code that passes a Context where impl Spanned is expected, even though callers using the method directly are unaffected. The CRATE_DATA_CACHE hard-fail behaviour and the get_attr_str delimiter assumption are lower-stakes concerns.

lang/syn/src/lib.rs — the Spanned trait removal; lang/syn/src/idl/defined.rs — the delimiter assumption in get_attr_str

Important Files Changed

Filename	Overview
lang/syn/src/lib.rs	Core syn 2.0 migrations: parse_terminated separator added, instruction_api type changed from Punctuated<Expr> to Punctuated<FnArg>, trailing-comma handling moved to pop_punct(), and impl Spanned for Context<T> replaced with an inherent pub fn span() — a breaking change for downstream consumers.
lang/syn/src/idl/defined.rs	CRATE_DATA_CACHE changed from OnceLock<Option<…>> (silent-fail) to OnceLock<Result<…, String>> (hard-fail); get_attr_str now only processes Meta::List variants, which is correct for repr and derive attrs in practice.
lang/syn/src/parser/context.rs	Safety-check doc-comment detection and #[derive(Accounts)] filter both correctly migrated from tokenizer-level iteration to structured syn 2.0 Meta pattern matches.
lang/derive/serde/src/lib.rs	extract_borsh_attrs migrated from NestedMeta to syn::Meta; silently swallows parse errors via unwrap_or_default(), matching the pre-existing silent behavior.
lang/syn/src/codegen/accounts/try_accounts.rs	Expr::Type → FnArg::Typed migration is correct: arg.pat replaces expr_type.expr and arg.ty replaces expr_type.ty with equivalent quoting behavior.
lang/attribute/account/src/lib.rs	#[accessor] and #[repr] attribute parsing migrated cleanly from token-stream iteration to structured attr.meta matching; bytemuck derive detection correctly scoped to derive attrs only.
lang/syn/src/parser/docs.rs	Doc-comment extraction migrated from parse_meta() to direct attr.meta pattern matching; CHECK: filtering logic is preserved correctly.
lang/syn/src/parser/error.rs	#[msg] and #[doc] attribute handling correctly migrated from token-stream group extraction to Meta::List::tokens.
tests/idl-forward-ref/programs/idl-forward-ref/src/lib.rs	New regression test program using precise-capture + use<T> syntax and a forward-referenced type; correctly exercises the CRATE_DATA_CACHE path that previously triggered the silent-fail bug.

Sequence Diagram

sequenceDiagram
    participant PM as Proc-macro crate
    participant AS as anchor-syn
    participant CC as CrateContext::parse
    participant OL as OnceLock Cache

    PM->>AS: "gen_idl_type(Updates)"
    AS->>OL: get_or_init
    OL->>CC: "parse(&lib_path) via syn 2.0"
    CC-->>OL: "Ok(ctx) - handles use T syntax"
    OL-->>AS: "Ok(CachedCrateData)"
    AS-->>PM: "correct IDL tokens"

    Note over CC,OL: On parse failure
    CC-->>OL: "Err(e) - cached permanently"
    OL-->>AS: "Err(msg)"
    AS-->>PM: "compile_error! Failed to parse crate"

Loading

_{Reviews (1): Last reviewed commit: "fix(lang/syn): migrate anchor-syn and pr..." | Re-trigger Greptile}

[Copilot]

Pull request overview

Upgrades Anchor’s Rust parsing/codegen pipeline (anchor-syn and dependent proc-macro crates) from syn v1 to syn v2 to support modern Rust syntax during IDL generation, and restores hard-fail behavior when crate parsing cannot be performed.

Changes:

• Migrate anchor-syn + proc-macro crates to syn = 2 and update parsing APIs (attr.path(), attr.meta, new parse_terminated signature, etc.).
• Change IDL type generation to hard-error when CrateContext::parse fails (instead of silently falling back).
• Add a regression test program (tests/idl-forward-ref) exercising Rust 1.82+ precise-capture syntax (+ use<T>).

Reviewed changes

Copilot reviewed 28 out of 29 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/idl-forward-ref/programs/idl-forward-ref/src/lib.rs	New minimal Anchor program reproducing forward-ref + IDL parsing scenario.
tests/idl-forward-ref/programs/idl-forward-ref/src/helper.rs	New module using Rust 1.82+ precise-capture syntax for regression coverage.
tests/idl-forward-ref/programs/idl-forward-ref/Cargo.toml	New test crate manifest with idl-build feature.
lang/syn/src/parser/program/instructions.rs	Update attribute path handling for syn 2.
lang/syn/src/parser/error.rs	Migrate error attribute parsing from token streams to attr.meta.
lang/syn/src/parser/docs.rs	Migrate doc parsing to syn 2 MetaNameValue representation.
lang/syn/src/parser/context.rs	Update safety-check attribute inspection and derive parsing to syn 2.
lang/syn/src/parser/accounts/mod.rs	Switch #[instruction(...)] parsing to syn 2-compatible representation.
lang/syn/src/parser/accounts/constraints.rs	Update attribute path handling for syn 2.
lang/syn/src/lib.rs	syn 2 API updates (parse_terminated), instruction API type change, and Context span API change.
lang/syn/src/idl/defined.rs	Update attribute token extraction and restore hard-fail on crate-parse errors (cached).
lang/syn/src/codegen/accounts/try_accounts.rs	Adjust codegen for new instruction-arg representation.
lang/syn/src/codegen/accounts/mod.rs	Update lifetime generic parsing to LifetimeParam.
lang/syn/Cargo.toml	Bump syn dependency to v2.
lang/derive/space/src/lib.rs	Update parsing helper to syn 2 parse_terminated API + path().
lang/derive/space/Cargo.toml	Bump syn to v2 and enable needed features.
lang/derive/serde/src/lib.rs	Replace NestedMeta usage with syn 2 Meta handling.
lang/derive/serde/Cargo.toml	Bump syn to v2.
lang/derive/accounts/Cargo.toml	Bump syn to v2.
lang/attribute/program/Cargo.toml	Bump syn to v2.
lang/attribute/event/Cargo.toml	Bump syn to v2.
lang/attribute/error/Cargo.toml	Bump syn to v2.
lang/attribute/constant/Cargo.toml	Bump syn to v2.
lang/attribute/account/src/lib.rs	Update parsing/token handling to syn 2 meta/path().
lang/attribute/account/Cargo.toml	Bump syn to v2.
lang/attribute/access-control/Cargo.toml	Bump syn to v2.
CHANGELOG.md	Document syn 2 migration + IDL generation fix.
Cargo.toml	Add the new idl-forward-ref test crate to the workspace.
Cargo.lock	Lockfile updates for syn 2 and new workspace member.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[eteen12]

fixed the issues the bots left for me

[eteen12]

working on passing the tests

[jamie-osec]

Can you additionally move syn to workspace.dependencies to avoid versions desyncing?

[eteen12]

@jamie-osec sure thing, made the changes and lets see if i pass all CI tests 🤞

[eteen12]

all tests passed and ready for review

[jamie-osec]

Directionally looks good, please address the review comments by me and the AIs.