#[builder(on(_, transparent))] attribute

[Veetaha]

Implements the #[builder(on(_, transparent)] that is part of #35.

Unfortunately, this initial implementation is a bit limited (but still useful!). There are two restrictions:

• It's only possible to specify #[builder(on(_, transparent))] with an _ pattern. No other patterns will be accepted (compile error)
• It's only possible to specify transparent in the first on. This doesn't compile: #[builder(on(String, into), on(_, transparent))]. Reorder the clauses to this instead: #[builder(on(_, transparent), on(String, into))]

I decided to postpone the extended design #152 for on for later. It's a really complex feature that I'd rather not do as part of the initial 3.0. It's possible to implement that in a minor release (no breaking changes are expected).

This PR doesn't include the documentation for this feature. The docs for all the new behaviors and attributes will be submitted in a separate PR.

Summary by CodeRabbit

• Bug Fixes
  • Improved error messages for the #[builder(...)] attribute usage, addressing redundancy, unsupported syntax, and nested attributes.
  • Clarified requirements for on(...) clauses, including order and parameter specifications.
  • Enhanced guidance for using the transparent option within on(...) clauses.

[coderabbitai]

Walkthrough

The changes in this pull request focus on error messages related to the #[builder(...)] attribute in Rust code, specifically within the file tests/integration/ui/compile_fail/attr_on.rs. The modifications clarify various issues such as redundant attributes, unsupported syntax, nested attributes, and errors related to the use of on(...) clauses. Additionally, the changes provide clearer guidance on the correct usage of the transparent option and the order of clauses, enhancing the understanding of the attribute's requirements.

Changes

File Path	Change Summary
bon/tests/integration/ui/compile_fail/attr_on.rs	- Added error messages for redundant attributes (#[builder(into)], #[builder(overwritable)]).
	- Introduced errors for unsupported syntax in #[builder(on(&dyn std::fmt::Debug, into))].
	- Highlighted that nested attributes are not allowed in #[builder(on(type_pattern, ...))].
	- Addressed issues with empty on attributes (e.g., #[builder(on)], #[builder(on())]).
	- Raised errors for missing commas and incorrect usage of on(...) clauses.
	- Clarified error messages regarding behavior overrides with #[builder(on(type_pattern, ...))].
	- Indicated that certain on(...) clauses are out of order.
	- Specified that transparent can only be used in the first on(...) clause with wildcard types.

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant Compiler
    participant ErrorHandler

    User->>Compiler: Submit Rust code with #[builder(...)]
    Compiler->>ErrorHandler: Check for attribute errors
    ErrorHandler->>Compiler: Return error messages for:
    ErrorHandler-->>User: Display errors (redundant attributes, unsupported syntax, etc.)

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL

📥 Commits

Files that changed from the base of the PR and between 62e3b9c and f9a3b76.

⛔ Files ignored due to path filters (6)

• bon-macros/src/builder/builder_gen/input_struct.rs is excluded by !**/*.rs
• bon-macros/src/builder/builder_gen/member/named.rs is excluded by !**/*.rs
• bon-macros/src/builder/builder_gen/top_level_config/mod.rs is excluded by !**/*.rs
• bon-macros/src/builder/builder_gen/top_level_config/on.rs is excluded by !**/*.rs
• bon/tests/integration/builder/attr_transparent.rs is excluded by !**/*.rs
• bon/tests/integration/ui/compile_fail/attr_on.rs is excluded by !**/*.rs

📒 Files selected for processing (1)

• bon/tests/integration/ui/compile_fail/attr_on.stderr (1 hunks)

🔇 Additional comments (4)

bon/tests/integration/ui/compile_fail/attr_on.stderr (4)

45-52: LGTM: Clear and accurate error message

The error message has been updated to include 'transparent' in the list of available options, which aligns well with the new feature implementation.

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53-70: LGTM: Clear clause ordering enforcement

The error messages effectively communicate that on(...) clauses must be consecutive, which helps maintain a consistent attribute structure.

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71-81: LGTM: Proper enforcement of transparent restrictions

The error messages accurately implement the PR's documented limitations by:

1. Enforcing that transparent can only be used in the first on(...) clause
2. Restricting transparent to only work with the wildcard pattern (_)

The messages also helpfully indicate these are temporary restrictions that may be lifted in the future, which aligns with the PR objectives of postponing more complex designs for a future release.

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Line range hint 1-81: Verify comprehensive error coverage

Let's ensure all error cases are covered and consistent with the codebase style.

✅ Verification successful

All error cases are properly covered and consistent with codebase style

The verification shows that:

1. The error messages in attr_on.stderr follow the consistent style pattern of "error: " prefix used throughout the codebase
2. All error cases for transparent attribute are properly covered, including:
   • Redundant attributes with on(...)
   • Order restrictions
   • Type pattern restrictions
3. The error messages maintain a clear, descriptive format that explains both the issue and, where applicable, the solution
4. The error cases align with the documented behavior in the codebase, as evidenced by the implementation comments and tests

The error coverage is comprehensive and the messages follow the established style conventions of the codebase.

🏁 Scripts executed

The following scripts were executed for the analysis:

Script:

#!/bin/bash
# Description: Check for consistency in error messages and coverage

# Test 1: Check if there are similar error messages in other test files
echo "Checking for similar error patterns in other test files..."
rg -l "builder.*transparent" tests/

# Test 2: Verify error message style consistency
echo "Checking error message style consistency..."
rg "^error: " tests/ | sort | uniq -c | sort -nr

# Test 3: Look for any TODO/FIXME comments related to error messages
echo "Checking for TODO/FIXME comments in error handling..."
rg -i "todo|fixme|xxx|hack" tests/ -g "*.rs" -g "*.stderr"

Length of output: 631

---

Script:

#!/bin/bash
# Let's try with the correct path structure by first finding the test files

# Find all test files
echo "Finding test files..."
fd -t f . -e rs -e stderr

# Once we find the files, let's check error patterns
echo -e "\nChecking error patterns..."
rg "builder.*transparent" .

# Check error message style
echo -e "\nChecking error message style..."
rg "^error: " .

# Look for TODOs
echo -e "\nChecking TODOs..."
rg -i "todo|fixme|xxx|hack" . -g "*.rs" -g "*.stderr"

Length of output: 42040

---

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