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 - Start each package-level name that belongs to one feature or
  19   integration with the name of that feature. Start the names of its
  20   files with the same name. Keep a name generic only when more than one
  21   feature uses it.
  22 - Write type names with a capital letter, so that a variable can have
  23   the name of its type. Write all other package-level names in lower
  24   case.
  25 - Write all the letters of an initialism in one case.
  26 - Put entry points first, then each struct's methods as a group, then
  27   standalone utility functions. Do not put a utility function between
  28   the methods of one type.
  29 - In each group, order functions by first use in the file.
  30
  31 ## Entry point and context
  32
  33 - `main` calls `run()` and handles its returned error. Do not use
  34   `log.Fatal`.
  35 - `run()` creates the SIGINT/SIGTERM signal context and defers its
  36   cancellation. Pass that context through operations and let cleanup
  37   finish before `main` exits.
  38 - Use `ctx` for a context and `cancel` for its cancellation function.
  39   Call `defer cancel()` immediately after you create the context.
  40 - Reuse `ctx` when a child context replaces its parent. Use a different
  41   name only when both contexts stay in use. Return `ctx.Err()` directly.
  42
  43 ## Errors
  44
  45 - Handle every returned error.
  46 - Reuse an existing `err` for later operations in the same scope. Use a
  47   different variable only to keep or join errors.
  48 - Use `errors.Is` and `errors.As` to examine errors. Do not compare an
  49   error directly with a sentinel, because errors can be wrapped.
  50 - When a function has more than one error path, wrap each returned error
  51   with the context of its operation. A function with one error path can
  52   return the error directly.
  53 - When deferred cleanup can fail, use a named `err` result and join the
  54   cleanup error with `errors.Join`.
  55
  56 ## Style
  57
  58 - Keep function signatures on one line. Write function bodies on more
  59   than one line, also for anonymous functions, deferred cleanup, and
  60   test callbacks.
  61 - Do not use short `if` initializers.
  62 - Use a one-letter receiver name for each method.
  63 - Use field names in struct literals. Put each field on its own line
  64   when you set more than one field. This includes the cases of a
  65   table-driven test. A small type of two fields that acts as one value,
  66   such as a key or a coordinate pair, can use a positional literal on
  67   one line.
  68 - Put an empty line between logical blocks, also after multiline
  69   declarations, assignments, literals, and calls. Keep an operation with
  70   its immediate error or result check. Keep a short declaration with its
  71   immediate use.
  72 - Use GNU-style command flags: two dashes for long flags, such as
  73   `--cwd`, and one dash only for one-letter flags, such as `-h`.
  74 - Prefer the Go standard library. Prefer Go over cgo.
  75 - Do not add compile-time interface assertions. Prove compatibility
  76   through actual assignments and calls.
  77 - Use `// nolint: name` for lint directives.
  78
  79 ## Dependencies
  80
  81 - After a change to `go.mod` or `go.sum`, update `vendorHash` in
  82   `nix/package.nix`. While the module has no dependencies, `vendorHash`
  83   is `null`.
  84
  85 ## Tests
  86
  87 - Add tests for meaningful behavior. Do not add tests that only repeat
  88   implementation details.
  89 - Use `testify/require` for assertions.
  90 - Name a table-driven case slice `testCases` and its range variable
  91   `tc`. A subtest name describes the behavior, not a generic outcome or
  92   input.
  93 - In a test file, put constants immediately after the imports, then the
  94   tests, then supporting types, methods, and helpers.
  95 - Keep a helper that only one test file uses in that file. Put a helper
  96   that more than one test file uses in a file without tests. Name that
  97   file for what it holds, and end the name with `_helper_test.go`.
  98 - Supply valid required dependencies in tests. Do not make a dependency
  99   optional only to make a test simpler.