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diff --git a/content/notes/working-with-go.md b/content/notes/working-with-go.md new file mode 100644 index 0000000..b5e690e --- /dev/null +++ b/content/notes/working-with-go.md @@ -0,0 +1,286 @@ +--- +title: Working with Go +date: 2021-08-05 +tags: + - emacs + - go +--- + +*This document assumes go version \>= 1.16*. + +# Go Modules + +[Go modules](https://blog.golang.org/using-go-modules) have been added +in 2019 with Go 1.11. A number of changes were introduced with [Go +1.16](https://blog.golang.org/go116-module-changes). This document is a +reference for me so that I can find answers to things I keep forgetting. + +## Creating a new module + +To create a new module, run `go mod init golang.fcuny.net/m`. This will +create two files: `go.mod` and `go.sum`. + +In the `go.mod` file you'll find: + +- the module import path (prefixed with `module`) +- the list of dependencies (within `require`) +- the version of go to use for the module + +## Versioning + +To bump the version of a module: + +``` bash +$ git tag v1.2.3 +$ git push --tags +``` + +Then as a user: + +``` bash +$ go get -d golang.fcuny.net/m@v1.2.3 +``` + +## Updating dependencies + +To update the dependencies, run `go mod tidy` + +## Editing a module + +If you need to modify a module, you can check out the module in your +workspace (`git clone <module URL>`). + +Edit the `go.mod` file to add + +``` go +replace <module URL> => <path of the local checkout> +``` + +Then modify the code of the module and the next time you compile the +project, the cloned module will be used. + +This is particularly useful when trying to debug an issue with an +external module. + +## Vendor-ing modules + +It's still possible to vendor modules by running `go mod vendor`. This +can be useful in the case of a CI setup that does not have access to +internet. + +## Proxy + +As of version 1.13, the variable `GOPROXY` defaults to +`https://proxy.golang.org,direct` (see +[here](https://github.com/golang/go/blob/c95464f0ea3f87232b1f3937d1b37da6f335f336/src/cmd/go/internal/cfg/cfg.go#L269)). +As a result, when running something like +`go get golang.org/x/tools/gopls@latest`, the request goes through the +proxy. + +There's a number of ways to control the behavior, they are documented +[here](https://golang.org/ref/mod#private-modules). + +There's a few interesting things that can be done when using the proxy. +There's a few special URLs (better documentation +[here](https://golang.org/ref/mod#goproxy-protocol)): + +| path | description | +|-----------------------|------------------------------------------------------------------------------------------| +| $mod/@v/list | Returns the list of known versions - there's one version per line and it's in plain text | +| $mod/@v/$version.info | Returns metadata about a version in JSON format | +| $mod/@v/$version.mod | Returns the `go.mod` file for that version | + +For example, looking at the most recent versions for `gopls`: + +``` bash +; curl -s -L https://proxy.golang.org/golang.org/x/tools/gopls/@v/list|sort -r|head +v0.7.1-pre.2 +v0.7.1-pre.1 +v0.7.1 +v0.7.0-pre.3 +v0.7.0-pre.2 +v0.7.0-pre.1 +v0.7.0 +v0.6.9-pre.1 +v0.6.9 +v0.6.8-pre.1 +``` + +Let's check the details for the most recent version + +``` bash +; curl -s -L https://proxy.golang.org/golang.org/x/tools/gopls/@v/list|sort -r|head +v0.7.1-pre.2 +v0.7.1-pre.1 +v0.7.1 +v0.7.0-pre.3 +v0.7.0-pre.2 +v0.7.0-pre.1 +v0.7.0 +v0.6.9-pre.1 +v0.6.9 +v0.6.8-pre.1 +``` + +And let's look at the content of the `go.mod` for that version too: + +``` bash +; curl -s -L https://proxy.golang.org/golang.org/x/tools/gopls/@v/v0.7.1-pre.2.mod +module golang.org/x/tools/gopls + +go 1.17 + +require ( + github.com/BurntSushi/toml v0.3.1 // indirect + github.com/google/go-cmp v0.5.5 + github.com/google/safehtml v0.0.2 // indirect + github.com/jba/templatecheck v0.6.0 + github.com/sanity-io/litter v1.5.0 + github.com/sergi/go-diff v1.1.0 + golang.org/x/mod v0.4.2 + golang.org/x/sync v0.0.0-20210220032951-036812b2e83c // indirect + golang.org/x/sys v0.0.0-20210510120138-977fb7262007 + golang.org/x/text v0.3.6 // indirect + golang.org/x/tools v0.1.6-0.20210802203754-9b21a8868e16 + golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect + honnef.co/go/tools v0.2.0 + mvdan.cc/gofumpt v0.1.1 + mvdan.cc/xurls/v2 v2.2.0 +) +``` + +# Tooling + +## LSP + +`gopls` is the default implementation of the language server protocol +maintained by the Go team. To install the latest version, run +`go install golang.org/x/tools/gopls@latest` + +## `staticcheck` + +[`staticcheck`](https://staticcheck.io/) is a great tool to run against +your code to find issues. To install the latest version, run +`go install honnef.co/go/tools/cmd/staticcheck@latest`. + +# Emacs integration + +## `go-mode` + +[This is the mode](https://github.com/dominikh/go-mode.el) to install to +get syntax highlighting (mostly). + +## Integration with LSP + +Emacs has a pretty good integration with LSP, and ["Eglot for better +programming experience in +Emacs"](https://whatacold.io/blog/2022-01-22-emacs-eglot-lsp/) is a good +starting point. + +### eglot + +[This is the main mode to install](https://github.com/joaotavora/eglot). + +The configuration is straightforward, this is what I use: + +``` elisp +;; for go's LSP I want to use staticcheck and placeholders for completion +(customize-set-variable 'eglot-workspace-configuration + '((:gopls . + ((staticcheck . t) + (matcher . "CaseSensitive") + (usePlaceholders . t))))) + +;; ensure we load eglot for some specific modes +(dolist (hook '(go-mode-hook nix-mode-hook)) + (add-hook hook 'eglot-ensure)) +``` + +`eglot` integrates well with existing modes for Emacs, mainly xref, +flymake, eldoc. + +# Profiling + +## pprof + +[pprof](https://github.com/google/pprof) is a tool to visualize +performance data. Let's start with the following test: + +``` go +package main + +import ( + "strings" + "testing" +) + +func BenchmarkStringJoin(b *testing.B) { + input := []string{"a", "b"} + for i := 0; i <= b.N; i++ { + r := strings.Join(input, " ") + if r != "a b" { + b.Errorf("want a b got %s", r) + } + } +} +``` + +Let's run a benchmark with +`go test . -bench=. -cpuprofile cpu_profile.out`: + +``` go +goos: linux +goarch: amd64 +pkg: golang.fcuny.net/m +cpu: Intel(R) Core(TM) i3-1005G1 CPU @ 1.20GHz +BenchmarkStringJoin-4 41833486 26.85 ns/op 3 B/op 1 allocs/op +PASS +ok golang.fcuny.net/m 1.327s +``` + +And let's take a look at the profile with +`go tool pprof cpu_profile.out` + +``` bash +File: m.test +Type: cpu +Time: Aug 15, 2021 at 3:01pm (PDT) +Duration: 1.31s, Total samples = 1.17s (89.61%) +Entering interactive mode (type "help" for commands, "o" for options) +(pprof) top +Showing nodes accounting for 1100ms, 94.02% of 1170ms total +Showing top 10 nodes out of 41 + flat flat% sum% cum cum% + 240ms 20.51% 20.51% 240ms 20.51% runtime.memmove + 220ms 18.80% 39.32% 320ms 27.35% runtime.mallocgc + 130ms 11.11% 50.43% 450ms 38.46% runtime.makeslice + 110ms 9.40% 59.83% 1150ms 98.29% golang.fcuny.net/m.BenchmarkStringJoin + 110ms 9.40% 69.23% 580ms 49.57% strings.(*Builder).grow (inline) + 110ms 9.40% 78.63% 1040ms 88.89% strings.Join + 70ms 5.98% 84.62% 300ms 25.64% strings.(*Builder).WriteString + 50ms 4.27% 88.89% 630ms 53.85% strings.(*Builder).Grow (inline) + 40ms 3.42% 92.31% 40ms 3.42% runtime.nextFreeFast (inline) + 20ms 1.71% 94.02% 20ms 1.71% runtime.getMCache (inline) +``` + +We can get a breakdown of the data for our module: + +``` bash +(pprof) list golang.fcuny.net +Total: 1.17s +ROUTINE ======================== golang.fcuny.net/m.BenchmarkStringJoin in /home/fcuny/workspace/gobench/app_test.go + 110ms 1.15s (flat, cum) 98.29% of Total + . . 5: "testing" + . . 6:) + . . 7: + . . 8:func BenchmarkStringJoin(b *testing.B) { + . . 9: b.ReportAllocs() + 10ms 10ms 10: input := []string{"a", "b"} + . . 11: for i := 0; i <= b.N; i++ { + 20ms 1.06s 12: r := strings.Join(input, " ") + 80ms 80ms 13: if r != "a b" { + . . 14: b.Errorf("want a b got %s", r) + . . 15: } + . . 16: } + . . 17:} +``` |