git.giacomolli.uk - onechat/blob - .agents/skills/go-code/SKILL.md

   1 ---
   2 name: go-code
   3 description: Go style rules. Use before you write or review Go code.
   4 ---
   5
   6 # Go code
   7
   8 ## Packages and files
   9
  10 - Keep Go code in one root `main` package. Do not add `internal/`,
  11   `cmd/`, or one-file packages until the user asks for them.
  12 - Keep `main.go` limited to the entry point. Name other files for their
  13   function. Do not create `main_test.go`.
  14 - A file carries its own context. Keep each struct and all of its
  15   methods in one file. Give a separate responsibility its own type.
  16 - When code in one file gets a user in another file for an unrelated
  17   purpose, move it to a file named for its function in the same change.
  18 - Put entry points first, then each struct's methods as a group, then
  19   standalone utility functions. Do not put a utility function between
  20   the methods of one type.
  21 - In each group, order functions by first use in the file.
  22
  23 ## Entry point and context
  24
  25 - `main` calls `run()` and handles its returned error. Do not use
  26   `log.Fatal`.
  27 - `run()` creates the SIGINT/SIGTERM signal context and defers its
  28   cancellation. Pass that context through operations and let cleanup
  29   finish before `main` exits.
  30 - Use `ctx` for a context and `cancel` for its cancellation function.
  31   Call `defer cancel()` immediately after you create the context.
  32 - Reuse `ctx` when a child context replaces its parent. Use a different
  33   name only when both contexts stay in use. Return `ctx.Err()` directly.
  34
  35 ## Errors
  36
  37 - Handle every returned error.
  38 - Reuse an existing `err` for later operations in the same scope. Use a
  39   different variable only to keep or join errors.
  40 - Use `errors.Is` and `errors.As` to examine errors. Do not compare an
  41   error directly with a sentinel, because errors can be wrapped.
  42 - When a function has more than one error path, wrap each returned error
  43   with the context of its operation. A function with one error path can
  44   return the error directly.
  45 - When deferred cleanup can fail, use a named `err` result and join the
  46   cleanup error with `errors.Join`.
  47
  48 ## Style
  49
  50 - Keep function signatures on one line. Write function bodies on more
  51   than one line, also for anonymous functions, deferred cleanup, and
  52   test callbacks.
  53 - Do not use short `if` initializers.
  54 - Use a one-letter receiver name for each method.
  55 - Use field names in struct literals. Put each field on its own line
  56   when you set more than one field. This includes the cases of a
  57   table-driven test. A small type of two fields that acts as one value,
  58   such as a key or a coordinate pair, can use a positional literal on
  59   one line.
  60 - Put an empty line between logical blocks, also after multiline
  61   declarations, assignments, literals, and calls. Keep an operation with
  62   its immediate error or result check. Keep a short declaration with its
  63   immediate use.
  64 - Use GNU-style command flags: two dashes for long flags, such as
  65   `--cwd`, and one dash only for one-letter flags, such as `-h`.
  66 - Prefer the Go standard library. Prefer Go over cgo.
  67 - Do not add compile-time interface assertions. Prove compatibility
  68   through actual assignments and calls.
  69 - Use `// nolint: name` for lint directives.
  70
  71 ## Dependencies
  72
  73 - After a change to `go.mod` or `go.sum`, update `vendorHash` in
  74   `nix/package.nix`. While the module has no dependencies, `vendorHash`
  75   is `null`.
  76
  77 ## Tests
  78
  79 - Add tests for meaningful behavior. Do not add tests that only repeat
  80   implementation details.
  81 - Use `testify/require` for assertions.
  82 - Name a table-driven case slice `testCases` and its range variable
  83   `tc`. A subtest name describes the behavior, not a generic outcome or
  84   input.
  85 - In a test file, put constants immediately after the imports, then the
  86   tests, then supporting types, methods, and helpers.
  87 - Supply valid required dependencies in tests. Do not make a dependency
  88   optional only to make a test simpler.