resolc: Detect undeployable contracts at link time

[dimartiro]

Description

Closes #96

A contract whose linked blob exceeds the target runtime's limits compiles fine and is then rejected by pallet_revive on deployment. This reproduces the pallet's checks at link time so the problem surfaces where it can still be acted on.

What it checks

pallet_revive::limits::code::enforce rejects a blob on four grounds the compiler can evaluate: the blob length (BLOB_BYTES), the longest basic block (BASIC_BLOCK_SIZE), and the purgeable and baseline interpreter memory (PURGABLE_MEMORY_LIMIT, BASELINE_MEMORY_LIMIT). All four are now checked, and each reports the measured value against the limit it broke.

The memory figures are not approximated. The pallet derives them from ProgramBlob::estimate_interpreter_memory_usage, and revive already depends on polkavm-common, so crates/linker/src/limits.rs calls the same API with the same arguments and reaches the same verdict rather than a conservative guess.

Interface

• --memory-limit <BYTES>: the target runtime's baseline interpreter memory budget, defaulting to Asset Hub's. The compiler cannot know which runtime a blob is destined for, and the same chain at a different runtime version can carry a different budget.
• --ignore-memory-limit: report violations as warnings and emit the contract anyway.

Exceeding the budget is an error by default, on the grounds that a contract which cannot be deployed is not a useful build artifact.

Why this matters in practice

The baseline budget is where it bites, and it is easy to cross without touching a line of Solidity, because the static heap and stack buffers are part of it. Compiling Baseline.sol unchanged:

--heap-size	baseline memory	verdict
64 KiB	201,542	ok
256 KiB	398,150	ok
1 MiB	1,184,582	ok
2 MiB	2,233,159	over the 1,572,864 budget

Before this change the last row compiled successfully and produced a contract that could never be deployed. It now fails with the numbers and a pointer at the knob to turn:

Error: Baseline.sol:Baseline cannot be deployed to the target runtime: the contract needs 2233159 bytes of baseline interpreter memory but the runtime provides at most 1572864 bytes; the static heap and stack buffers are part of this budget, so lowering `--heap-size` or `--stack-size` frees room for code. Pass `--ignore-memory-limit` to compile anyway, or `--memory-limit` if the target runtime has a different budget.

[xermicus]

Thanks for the PR!

[xermicus]

Build::write_to_standard_json considers errors, so does this doesn't work in std json mode? Would be nice to have a test for that too.

[dimartiro]

Good catch — it didn't. write_to_standard_json only forwarded errors from results and dropped messages, which is where the deployment-limit diagnostics (and other link-time issues) live.

They now land in the standard JSON errors array. Added coverage for --standard-json: the error, --ignore-memory-limit as a warning, and a larger --memory-limit.

Addressed in 98e6232.

[xermicus]

Instead of duplicating code here, we should re-use this from pallet-revive directly. It's already in the dependency tree.