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diff --git a/doc/development/go_guide/index.md b/doc/development/go_guide/index.md index f5b0da2f162..1a11321b70f 100644 --- a/doc/development/go_guide/index.md +++ b/doc/development/go_guide/index.md @@ -443,6 +443,43 @@ of the Code Review Comments page on the Go wiki for more details. Most editors/IDEs allow you to run commands before/after saving a file, you can set it up to run `goimports -local gitlab.com/gitlab-org` so that it's applied to every file when saving. +### Initializing slices + +If initializing a slice, provide a capacity where possible to avoid extra +allocations. + +<table> +<tr><th>:white_check_mark: Do</th><th>:x: Don't</th></tr> +<tr> + <td> + + ```golang + s2 := make([]string, 0, size) + for _, val := range s1 { + s2 = append(s2, val) + } + ``` + + </td> + <td> + + ```golang + var s2 []string + for _, val := range s1 { + s2 = append(s2, val) + } + ``` + + </td> +</tr> +</table> + +If no capacity is passed to `make` when creating a new slice, `append` +will continuously resize the slice's backing array if it cannot hold +the values. Providing the capacity ensures that allocations are kept +to a minimum. It is recommended that the [`prealloc`](https://github.com/alexkohler/prealloc) +golanci-lint rule automatically check for this. + ### Analyzer Tests The conventional Secure [analyzer](https://gitlab.com/gitlab-org/security-products/analyzers/) has a [`convert` function](https://gitlab.com/gitlab-org/security-products/analyzers/command/-/blob/main/convert.go#L15-17) that converts SAST/DAST scanner reports into [GitLab Security Reports](https://gitlab.com/gitlab-org/security-products/security-report-schemas). When writing tests for the `convert` function, we should make use of [test fixtures](https://dave.cheney.net/2016/05/10/test-fixtures-in-go) using a `testdata` directory at the root of the analyzer's repository. The `testdata` directory should contain two subdirectories: `expect` and `reports`. The `reports` directory should contain sample SAST/DAST scanner reports which are passed into the `convert` function during the test setup. The `expect` directory should contain the expected GitLab Security Report that the `convert` returns. See Secret Detection for an [example](https://gitlab.com/gitlab-org/security-products/analyzers/secrets/-/blob/160424589ef1eed7b91b59484e019095bc7233bd/convert_test.go#L13-66). |