fix(compile): compile only for the requested script context

[vadim-anfv]

The policy is compiled for all three script contexts one after another, before --type is looked at, and any of those failing aborts the command. So a policy that is valid for the type you asked for is rejected because it is invalid for one of the other two.

Here a 9-of-16 multisig is compiled with --type tr and fails on the legacy context: CHECKMULTISIG takes at most 15 keys, and what the compiler falls back to goes past MAX_SCRIPT_ELEMENT_SIZE, the 520-byte consensus limit. Taproot has no such limit.

$ cargo run --all-features -- compile "thresh(9,pk(a),pk(b),pk(c),pk(d),pk(e),pk(f),pk(g),pk(h),pk(i),pk(j),pk(k),pk(l),pk(m),pk(n),pk(o),pk(p))" --type tr

thread 'main' panicked at miniscript-12.3.7/src/policy/compiler.rs:506:52:
Terminal creation must always succeed: ContextError(MaxRedeemScriptSizeExceeded)

The fix moves the compilation into the matching branch, so only the requested context is compiled.

Changelog notice

• Fixed compile rejecting policies that are valid for the requested script type

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.09%. Comparing base (1282553) to head (6e64d8f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #317      +/-   ##
==========================================
+ Coverage   59.79%   60.09%   +0.29%     
==========================================
  Files          22       22              
  Lines        3878     3869       -9     
==========================================
+ Hits         2319     2325       +6     
+ Misses       1559     1544      -15     

Flag	Coverage Δ
rust	60.09% <100.00%> (+0.29%)	⬆️

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[Musab1258]

ACK 6ed624e

• I pulled the change locally and ran the new test, which passes. I confirmed it fails on master with the miniscript MaxRedeemScriptSizeExceeded panic. I also ran a 2-of-20 pk threshold policy manually with --all-features: --type tr returns a tr(…,multi_a(2,…)) descriptor and --type wsh returns a wsh(multi(2,…)) descriptor. On master, wsh panics on the same policy.

• I suggest you add a wsh test with the same policy. The fix helps wsh, but only tr is covered in tests.

• --type sh with a legacy-oversized policy (same 2-of-20) still panics inside miniscript 12.3.7 (compiler.rs:506, exit 101) instead of returning an error. Worth a follow-up, either an upstream rust-miniscript issue or a clean error in bdk-cli?

[vadim-anfv]

ACK 6ed624e

Thanks for testing!

I suggest you add a wsh test with the same policy. The fix helps wsh, but only tr is covered in tests.

Added the wsh case to the test with the same policy, so both contexts are covered now.

--type sh with a legacy-oversized policy (same 2-of-20) still panics inside miniscript 12.3.7 (compiler.rs:506, exit 101) instead of returning an error. Worth a follow-up, either an upstream rust-miniscript issue or a clean error in bdk-cli?

On --type sh: already fixed upstream. In 12.3.7 from_ast returns ContextError(MaxRedeemScriptSizeExceeded) for a 20-key threshold and the expect turns it into a panic. rust-bitcoin/rust-miniscript#828 dropped it, released in 13.0.0, and master handles it with if let Ok(...), skipping such a policy instead of aborting. bdk-cli is still on 12.3.7 through bdk_wallet, so we get this fix as soon as we move to miniscript 13.