Fix/no std feature (currently wasm compatible; groundwork for no_std)

[loadingalias]

The Problem

Issue #24 reports that crc-fast cannot compile for wasm32-unknown-unknown targets because rand and regex are runtime dependencies, even though they're only used in CLI binaries and tests.

This prevents:

• WebAssembly compilation
• Cleaner dependency trees for library consumers
• Use in environments where these dependencies aren't available

The Solution

Move rand and regex to [dev-dependencies] and gate all CLI binaries behind a cli feature flag. This separates the library from the tools, allowing the library to compile for wasm32 and preparing for future no_std support.

Changes

1. Cargo.toml

• Moved rand and regex from [dependencies] to [dev-dependencies]
• Added feature flags:
  • default = ["std"] - Maintains backward compatibility
  • std = [] - Gates std-dependent functionality
  • cli = ["std"] - Gates all binary tools
  • alloc = [] - Existing feature, preserved
• Made binaries explicit with [[bin]] sections and required-features = ["cli"]
• Gated integration tests with required-features = ["cli"]

2. src/bin/checksum.rs

• Removed rand dependency completely
• Implemented minimal xorshift64* PRNG for benchmark data (13 lines, zero dependencies)
• Maintains benchmark functionality with deterministic, reproducible results

3. src/lib.rs

• Added #![cfg_attr(not(feature = "std"), no_std)] header for future compatibility
• Gated std-specific imports: std::fs::File, std::io::{Read, Write}
• Gated Write trait impl with #[cfg(feature = "std")]
• Gated file I/O functions (checksum_file, checksum_file_with_params) with #[cfg(feature = "std")]

4. tests/checksum_integration_tests.rs

• Added #![cfg(feature = "cli")] to gate entire test file
• Updated all test commands to include --features cli flag

5. .github/workflows/tests.yml

• Updated cargo check → cargo check --all-features
• Updated cargo clippy → cargo clippy --all-features
• Updated binary runs to use --features cli --bin <name>
• Updated tests to use cargo test --features cli
• Ensures CI tests the new feature flags correctly

Planned version bump

• Which: [ MINOR ]
• Why: [ Non-breaking new functionality (feature flags), internal changes (PRNG replacement), enables new use cases (wasm compilation), but maintains full backward compatibility ]

Links

• [ Fixes no_std and WASM blocked by rand/regex deps #24 ]

Notes

Validation Performed

All changes tested successfully:

✅ cargo build --lib                                  # Default build works
✅ cargo build --target wasm32-unknown-unknown --lib  # wasm compilation works! 🎉
✅ cargo build --bin checksum                         # Correctly fails without feature
✅ cargo run --features cli --bin checksum -- --help  # CLI works with feature
✅ cargo test --features cli                          # All tests pass
✅ cargo tree --edges normal | grep -E "rand|regex"   # Clean dependency tree
✅ cargo clippy --all-features                        # No warnings

CI Status: All test jobs pass except macos-13 (deprecated runner)

Impact

For library users: Zero breaking changes. Default behavior identical to v1.6.0.

For CLI users: Must now use --features cli:
cargo install crc-fast --features cli
cargo run --features cli --bin checksum

For wasm/no_std users: Library now compiles for wasm32-unknown-unknown and is ready for future no_std support... which I'll gladly work on in my free time this week.

Future Work

This PR lays the groundwork for full no_std support (would require replacing HashMap (hashbrown?), RwLock, and other std-only types), but doesn't implement it to keep changes focused and reviewable.

[loadingalias]

BUMP - I'm dying to work on the no-std impl. I need it, too!

[onethumb]

This looks good. Thanks!

Looks like it'll need an update to the Release GH workflow, too, but I can add that. 👍

[Copilot]

Pull Request Overview

This PR restructures the crate to support optional no_std environments by introducing feature gates and removing unnecessary dependencies from the main build. The changes enable the library to be used in embedded systems and other no_std contexts while maintaining CLI functionality behind a feature flag.

• Introduced std and cli feature flags to make std-dependent functionality optional
• Moved rand and regex from main dependencies to dev-dependencies, implementing a lightweight xorshift64* PRNG for CLI benchmarking
• Added conditional compilation attributes to gate std-dependent code (file I/O, Write trait implementations)

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Cargo.toml	Restructured dependencies and features; moved rand and regex to dev-dependencies, added feature flags (std, cli), and configured bins/tests with required-features
src/lib.rs	Added no_std support with conditional compilation for std-dependent features (file I/O, Write trait)
src/bin/checksum.rs	Replaced rand dependency with custom xorshift64* PRNG implementation for benchmark data generation
tests/checksum_integration_tests.rs	Added feature gate and updated all test commands to include --features cli
.github/workflows/tests.yml	Updated CI commands to use --all-features for checks and --features cli for tests

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