[v2] fix(diagnostics): Gate yul builtins on version and target by teofr · Pull Request #2036 · NomicFoundation/slang

teofr · 2026-08-07T15:26:58Z

We were checking for redeclarations errors on Yul against builtin regardless of version and target, this is a problem since solc allows to use built ins as identifiers in yul before they become available (for example mcopy before Cancun).

This PR makes slang more lenient than solc, in particular we are lacking another concept of identifier checking, reserved identifiers. Within Yul, certain identifiers are reserved for future builtin, for example chainid was reserved even before the Istanbul fork. That remains as future work.

Two next PRs will tackle:

gating solidity builtins, not only yul builtins
Also gating builtin references, otherwise the following example fails (a bug already present, but exposed by this fix):

assembly {
    let mcopy := 1
    let x := mcopy   // Error: "This built-in was introduced in EVM target 'Cancun'"
}

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Pull request overview

This PR adjusts Slang v2’s Yul diagnostics so Yul built-in name redeclaration is only rejected when the built-in is actually available for the configured language version and EVM target (matching solc’s “grace period” behavior for names like mcopy before Cancun). It also introduces snapshot coverage documenting current intentional divergences where solc treats some identifiers as reserved even when the built-in is not available.

Changes:

Gate Yul built-in redeclaration checks on (LanguageVersion, EvmTarget) by threading both through p6_resolve_yul and using an availability predicate.
Centralize built-in version/target specifiers into a single generated source (built_in_specifiers) used by both availability checks and diagnostics validation.
Add/extend diagnostics snapshot suites to cover “not yet reserved”, “reserved before fork”, and “reserved after fork” cases (including expected solc divergences).

Reviewed changes

Copilot reviewed 21 out of 40 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_before_own_fork/input.sol	New snapshot input demonstrating `chainid` reserved-by-solc behavior before its fork.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_before_own_fork/generated/solc/0.8.0-failure.txt	Records solc’s failure diagnostic for the reserved identifier case.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_before_own_fork/generated/slang/0.8.0-success.txt	Records Slang’s current acceptance (documented divergence) for the reserved-before-availability case.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_before_own_fork/.tests.config.json	Configures matrix + expected solc divergence for the reserved-before-fork scenario.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/input.sol	New snapshot input demonstrating `difficulty` behavior across the Paris boundary.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/generated/solc/10-paris-failure.txt	Captures solc’s “reserved identifier” failure post-Paris.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/generated/solc/05-constantinople-failure.txt	Captures solc’s pre-Paris builtin-name identifier failure.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/generated/solc/01-homestead-failure.txt	Captures solc’s pre-Constantinople warnings + failure output for the same scenario.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/generated/solc/00-frontier-failure.txt	Captures solc’s invalid EVM target behavior for Frontier in the matrix.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/generated/slang/10-paris-success.txt	Records Slang’s current acceptance post-Paris (documented divergence).
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/generated/slang/00-frontier-failure.txt	Records Slang’s Frontier failure in this suite’s expectations.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/reserved_after_own_fork/.tests.config.json	Configures matrix + expected solc divergence for the reserved-after-own-fork scenario.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/input.sol	New snapshot input for `mcopy` grace-period behavior before Cancun.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/generated/solc/12-cancun-failure.txt	Captures solc’s failure once Cancun introduces the built-in.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/generated/solc/05-constantinople-failure.txt	Captures solc’s pre-Cancun warning output for `mcopy`.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/generated/solc/01-homestead-failure.txt	Captures solc warnings on older targets for the same case.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/generated/solc/00-frontier-failure.txt	Captures solc’s invalid EVM target behavior for Frontier in the matrix.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/generated/slang/12-cancun-failure.txt	Records Slang’s failure once the built-in becomes available (matches intent).
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/generated/slang/00-frontier-success.txt	Records Slang’s acceptance prior to built-in availability.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_yet_reserved_until_fork/.tests.config.json	Configures matrix + expected solc divergence (warnings/invalid-target handling).
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/input.sol	New snapshot input for `mcopy` one compiler version before introduction (always allowed).
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/generated/solc/12-cancun-failure.txt	Captures solc’s invalid EVM target behavior when the compiler predates Cancun.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/generated/solc/05-constantinople-success.txt	Captures solc success on supported targets for that older compiler version.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/generated/solc/01-homestead-failure.txt	Captures solc’s deprecation warning behavior in the matrix.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/generated/solc/00-frontier-failure.txt	Captures solc’s invalid EVM target behavior for Frontier in the matrix.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/generated/slang/00-frontier-success.txt	Records Slang acceptance for the older-version, pre-introduction case.
crates/solidity-v2/testing/snapshots/diagnostics_output/resolution/built_in_redeclaration/not_reserved_before_own_version/.tests.config.json	Configures matrix + expected solc divergence for the pre-introduction case.
crates/solidity-v2/outputs/cargo/tests/src/diagnostics_output/snapshots.generated.rs	Registers the newly added snapshot suites in the Rust test runner.
crates/solidity-v2/outputs/cargo/semantic/src/passes/tests/binder.rs	Updates binder pass test harness to call `p6_resolve_yul` with version + target.
crates/solidity-v2/outputs/cargo/semantic/src/passes/p8_code_analysis/built_ins/validate_built_ins.rs.jinja2	Removes the old codegen template for built-in validation (replaced by shared specifiers).
crates/solidity-v2/outputs/cargo/semantic/src/passes/p8_code_analysis/built_ins/validate_built_ins.rs	Adds non-generated validator that consumes centralized specifiers.
crates/solidity-v2/outputs/cargo/semantic/src/passes/p8_code_analysis/built_ins/validate_built_ins.generated.rs	Removes old generated validator implementation.
crates/solidity-v2/outputs/cargo/semantic/src/passes/p8_code_analysis/built_ins/mod.rs	Switches module wiring to use the new non-generated validator.
crates/solidity-v2/outputs/cargo/semantic/src/passes/p6_resolve_yul/mod.rs	Threads `LanguageVersion` + `EvmTarget` into the Yul resolution pass.
crates/solidity-v2/outputs/cargo/semantic/src/passes/p6_resolve_yul/conflicts.rs	Gates Yul built-in redeclaration conflicts on built-in availability.
crates/solidity-v2/outputs/cargo/semantic/src/context/mod.rs	Passes `language_version` and `evm_target` into `p6_resolve_yul::run` from the semantic pipeline.
crates/solidity-v2/outputs/cargo/semantic/src/built_ins/specifiers.rs.jinja2	New template: generates the single source of truth for built-in version/target specifiers.
crates/solidity-v2/outputs/cargo/semantic/src/built_ins/specifiers.generated.rs	Generated specifier mapping used by both diagnostics and availability.
crates/solidity-v2/outputs/cargo/semantic/src/built_ins/mod.rs	Adds availability + specifier modules and re-exports the shared helpers.
crates/solidity-v2/outputs/cargo/semantic/src/built_ins/availability.rs	Implements `is_built_in_available` based on the shared specifiers.

github-actions · 2026-08-07T15:42:37Z

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teofr · 2026-08-07T16:43:36Z

+        "specifier": {
+          "type": "Range",
+          "from": "Homestead",
+          "till": "Cancun"
+        },
+        "reason": "Before Cancun solc accepts `let mcopy := 1` with only a warning ('mcopy' will be promoted to a Yul reserved identifier in the future; plus a deprecated-EVM warning on the oldest targets), which counts as a rejection. slang correctly accepts the grace-period name until the built-in exists, so the statuses differ until warnings are distinguished from errors."
+      }


This should go away once we treat warnings as successes

teofr · 2026-08-07T16:47:40Z

-    // TODO: this checks against built-ins across all versions/targets, but we
-    // should restrict it to the current version/target.


This PR essentially solves this TODO, but opens a new one

Add Yul built-in redeclaration tests across the version and target axes

5bba1fa

teofr requested a review from Copilot August 7, 2026 15:27

Copilot started reviewing on behalf of teofr August 7, 2026 15:27 View session

Copilot AI reviewed Aug 7, 2026

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teofr commented Aug 7, 2026

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Gate Yul built-in name reservation by language version and EVM target

54cc152

teofr force-pushed the teofr/gate-yul-builtins branch from a8fd1b3 to 54cc152 Compare August 7, 2026 16:53

teofr marked this pull request as ready for review August 7, 2026 16:54

teofr requested review from a team as code owners August 7, 2026 16:54

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[v2] fix(diagnostics): Gate yul builtins on version and target - #2036

[v2] fix(diagnostics): Gate yul builtins on version and target#2036
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		// TODO: this checks against built-ins across all versions/targets, but we
		// should restrict it to the current version/target.

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