goadesign§goa

Imported from gencau/test-practices-agent-configurations (dataset/repos/goadesign§goa/AGENTS.md). Install upstream with npx skills add gencau/test-practices-agent-configurations --skill goadesign§goa. Copyright stays with the author.

Repository Guidelines

Common Rules

Agent Behavior

• Plan before acting: For ≤2 files, state a brief plan then implement. For ≥3 files, write a step-by-step plan first.
• Read before editing: Always read files before modifying. Search over guessing.
• Fix root causes: Do not produce local workarounds—fix the real issue.
• Be concise: Give short status updates during multi-step work. Present a short summary when done.

Go Code Style

• Go 1.24+. Format with go fmt ./....
• Imports: Group stdlib separate from external. Let gofmt manage ordering.
• Files: Use lower_snake_case.go. Keep ≤1000 lines; split proactively.
• Naming: Packages are lowercase and short. Exported identifiers need GoDoc. Avoid stutter.
• Types: Use any over interface{}. Prefer concrete types over interface{}.
• Errors: Wrap with %w. Use errors.Is/As. Never ignore errors or use _ = call().
• Signatures: Keep on one line when ≤100 columns. Only wrap genuinely long signatures.
• Slice/map nil: Do not check nil before len. len(nil) returns 0. Use len(x) == 0 directly.

Code Blocks and Literals

• Always place a newline after { and before } for if, for, switch, func, type.
• No single-line blocks: if cond { do() } → use multiple lines.
• Short struct literals are fine inline: &T{A: 1}. Break long literals to one field per line with trailing commas.

File Organization

Order declarations as:

1. Types (public, then private) in a single type (...) block when practical
2. Constants (public, then private)
3. Variables (public, then private)
4. Public functions
5. Public methods
6. Private functions
7. Private methods

No commented-out code—delete dead code.

Error Handling & Contracts

• Always check errors. Never discard with _.
• Strong contracts: Goa validates payloads at boundaries. Do not re-validate inside service code.
• No defensive programming: Do not add nil/empty guards for values guaranteed by construction, Goa, or prior validation.
• Validate only at boundaries: HTTP/gRPC handlers, event consumers, DB results, third-party APIs, ctx.Value(), type assertions, required map lookups.
• Fail fast: Unexpected states are bugs. Return precise errors or panic—do not silently recover or skip.

Goa DSL Rules

• Never edit gen/: Always regenerate.
• DSL validation: Put validations (lengths, enums, formats) in the design. Do not re-validate in code.
• Avoid Any: Use concrete types to enable gRPC generation.

Codegen Implementation

• Use NameScope helpers for type references: GoTypeRef, GoFullTypeRef, GoTypeName. Never concatenate strings for types.
• Let Goa decide pointer/value semantics. Do not force pointer=true except in transport validation.
• Keep helper visibility minimal: If logic is shared only inside one codegen area, keep it package-private or move it under an internal package. Do not export helpers from a parent package just to share them across sibling generators.
• Avoid pass-through wrappers: When two helper functions differ only by forwarding arguments or hard-coding nil, collapse them into a single implementation instead of adding an extra layer.

Documentation

• Every exported type, function, method, and field must have a GoDoc comment explaining its contract—like Go stdlib documentation.

Safety & Forbidden Operations

Testing

• Write table-driven tests in *_test.go.
• Name tests TestXxx. Keep fast and deterministic.
• Use testify/require for assertions.
• Prefer t.Errorf over t.Fatalf so tests report multiple failures.

Goa-Specific Rules

Project Structure

• dsl/: Public DSL definitions (dot imports allowed per .golangci.yml)
• expr/: Internal AST and validation
• codegen/: Generators for transports, types, docs
• http/, grpc/, jsonrpc/: Transport-specific codegen
• middleware/: Built-in interceptors
• pkg/: Core runtime
• cmd/goa/: CLI source

Build & Test

make lint          # Run linters
make test          # Run tests
cd cmd/goa && go install .  # Install CLI locally

Code Generation Behavior

• After modifying goa source, goa gen and goa example automatically compile and use your changes—no manual rebuild needed.
• goa gen deletes and recreates the entire gen/ directory.
• goa example only creates new files; it does not overwrite existing cmd/ files.

Repro Protocol

To reproduce a codegen issue:

1. Create ~/src/repros/<issue>/design/design.go
2. go mod init <issue> in the issue directory
3. goa gen <issue>/design
4. go mod tidy
5. go mod edit -replace goa.design/goa/v3=$HOME/src/goa
6. goa gen <issue>/design again with local goa
7. Optional: goa example <issue>/design

Slices/Maps and Required Fields

Do not rely on nil vs empty to encode presence. Goa uses omitempty—both nil and empty serialize as "missing". If empty is valid, do not mark the field as required.