rust

name	rust
description	Guides ccusage Rust implementation work. Use when editing rust/crates, native packaging, parser/module layout, pricing embedding, or Rust/TypeScript parity.
paths	["rust/**/*.rs","rust/**/*.toml","rust/**/build.rs"]
globs	rust/**/*.rs,rust/**/*.toml,rust/**/build.rs

ccusage Rust

Use this skill for the native Rust CLI under rust/crates/ccusage and rust/crates/ccusage-terminal.

Source Parity

Rust is the production implementation. Preserve existing Rust behavior unless the user explicitly scopes a behavior change. Before implementing or refactoring an agent, inspect the current Rust adapter and the agent source reference docs:

fd . rust/crates/ccusage/src/adapter/<agent>
sed -n '1,220p' rust/crates/ccusage/src/adapter/<agent>/README.md

When porting behavior from the historical TypeScript implementation, first find the relevant commit or tag that still contains apps/ccusage/src/adapter, then compare against that source. Do not assume origin/main still contains the TypeScript adapter.

Preserve report semantics, JSON fields, table columns, progress/spinner text, agent grouping, date filtering, --offline, CLAUDE_CONFIG_DIR, and source-specific environment variables.

Module Layout

Do not keep growing main.rs or single large adapter files. Use these responsibility boundaries where practical:

• adapter/<agent>/mod.rs - public adapter surface and command wiring.
• adapter/<agent>/paths.rs - environment variables, defaults, and path discovery.
• adapter/<agent>/parser.rs - raw record parsing and token/model mapping.
• adapter/<agent>/loader.rs - file walking, SQLite reads, dedupe, and date filtering entry points.
• adapter/<agent>/report.rs - JSON/table row shaping when agent-specific.
• shared modules stay in types.rs, summary.rs, output.rs, pricing.rs, progress.rs, and date_utils.rs.

Keep public pub(crate) surfaces narrow. Prefer moving tests with the code they exercise instead of leaving all Rust tests in main.rs.

When splitting large Rust modules or removing duplication, use the reduce-similarities skill, which runs similarity-rs for .rs files.

Pricing Embedding

TypeScript uses build/macro-time pricing snapshots. Rust should not rely on a manually edited claude-pricing.json as the only embedded source.

When changing pricing:

• Use the litellm flake input as the canonical pinned pricing revision for embedded pricing.
• For Nix builds, pass the locked LiteLLM model_prices_and_context_window.json to build.rs through CCUSAGE_PRICING_JSON_PATH.
• For non-Nix Cargo builds, have build.rs read the same litellm revision from flake.lock and fetch that pinned raw JSON at build time.
• Do not check generated LiteLLM pricing snapshots into the repository.
• Keep pricing JSON filtering and compacting in build.rs so runtime code loads the generated build-time snapshot first, then built-in model overrides, then runtime fetch when not --offline.
• Add tests for embedded/offline pricing and context limits.

Validation

Use the testing skill for Rust test commands. Use profile for performance work and branch-vs-main comparisons. For parity work, compare against the current main branch, a previous release, or a pinned historical TypeScript commit for a stable fixture window before changing behavior.