didc bind --target mo: emit PascalCase type names (Motoko convention)

[marc0olo]

Problem

didc bind --target mo emits snake_case type names, but the Motoko convention for types is PascalCase. This means generated bindings are not idiomatic Motoko and require a post-processing step to be usable in practice.

Example — current output:

public type canister_status_args = { canister_id : canister_id };
public type canister_status_result = { ... };

Expected idiomatic output:

public type CanisterStatusArgs = { canister_id : CanisterId };
public type CanisterStatusResult = { ... };

Note: record field labels and method names should stay snake_case — they are Candid identifiers, not Motoko identifiers. Only the type definition names and their references as types should be converted.

Context

This was discovered while maintaining caffeinelabs/mops-ic, the Motoko bindings package for the IC management canister. The initial generation in that repo was done with an undocumented post-processing step (snake→PascalCase); a follow-up PR (caffeinelabs/mops-ic#11) formalised this as scripts/pascal_types.py.

The Rust binding generator in didc already converts to PascalCase for struct/enum names (following Rust conventions). The Motoko generator should do the same.

Proposed fix

In rust/candid_parser/src/bindings/motoko.rs, convert type definition names (and their references) from snake_case to PascalCase when generating the public type declarations. Field labels (Label::Named) and method names should remain unchanged.

The conversion is straightforward: split on _, capitalise each word, join. The scripts/pascal_types.py in caffeinelabs/mops-ic#11 demonstrates the exact logic.

Additional note

didc 0.6.1 (current main) also fixes the float32 not supported in Motoko panic present in the released 0.5.4 binary — a release with both fixes would be very welcome.