tooling.slide

Go Tooling

Brian Ketelsen
me@brianketelsen.com
@bketelsen

Cory LaNou
@corylanou

* Better Code Quality through Tooling

Code quality is a hard thing.  Make it easy by using amazing tools that tell
you when you've done something that is usually considered a bad pracitice or
outright bug.

* go fmt

Gofmt formats Go programs. It uses tabs (width = 8) for indentation and blanks
for alignment.

Most editors have a plugin for this and you likely don't have to worry about it.

	go fmt ./...

.link https://golang.org/cmd/gofmt/

* go vet

Vet examines Go source code and reports suspicious constructs, such as Printf
calls whose arguments do not align with the format string. Vet uses heuristics
that do not guarantee all reports are genuine problems, but it can find errors
not caught by the compilers.

	go vet ./...

.link https://golang.org/cmd/vet/

* golint

Golint differs from gofmt. Gofmt reformats Go source code, whereas golint
prints out style mistakes.

While you should strive to satisfy Go Lint, it is opinionated, and not
everything is something you have to correct.

	go get -u github.com/golang/lint/golint
	golint ./...

.link https://github.com/golang/lint

* aligncheck, structcheck, and varcheck

- aligncheck finds inefficiently packed structs.
- structcheck finds unused struct fields
- varcheck finds unused global variables and constants.

	go get -u github.com/opennota/check/cmd/aligncheck
	go get -u github.com/opennota/check/cmd/structcheck
	go get -u github.com/opennota/check/cmd/varcheck

.link https://github.com/opennota/check

Known limitations: structcheck doesn't handle embedded structs yet.

* deadcode

Anyone want to guess what this tool does...

	go get -u github.com/tsenart/deadcode

.link https://github.com/tsenart/deadcode

* dupl

dupl is a tool written in Go for finding code clones. So far it can find clones
only in the Go source files. The method uses suffix tree for serialized ASTs.
It ignores values of AST nodes. It just operates with their types (e.g. if a ==
13 {} and if x == 100 {} are considered the same provided it exceeds the
minimal token sequence size).

	go get -u github.com/mibk/dupl

Examples:

  dupl -t 100
        Search clones in the current directory of size at least
        100 tokens.
  dupl $(find app/ -name '*_test.go')
        Search for clones in tests in the app directory.
  find app/ -name '*_test.go' |dupl -files
        The same as above.

.link http://github.com/mibk/dupl

* errcheck

errcheck is a program for checking for unchecked errors in go programs.

	go get -u github.com/kisielk/errcheck
	errcheck ./...

.link http://github.com/kisielk/errcheck

* gas

Inspects source code for security problems by scanning the Go AST.

	go get -u github.com/HewlettPackard/gas

	# Run a specific set of rules
	$ gas -include=G101,G203,G401 ./...

	# Run everything except for rule G303
	$ gas -exclude=G303 ./...

.link http://github.com/HewlettPackard/gas

* goconst

Find repeated strings that could be replaced by a constant.

	go get -u github.com/jgautheron/goconst/cmd/goconst
	goconst ./...

.link http://github.com/jgautheron/goconst

* gocyclo

Gocyclo calculates cyclomatic complexities of functions in Go source code.

The cyclomatic complexity of a function is calculated according to the following rules:

	1 is the base complexity of a function
	+1 for each 'if', 'for', 'case', '&&' or '||'

Install: 

	go get -u github.com/fzipp/gocyclo

Examples:

	gocyclo .
	gocyclo main.go
	gocyclo -top 10 src/
	gocyclo -over 25 docker
	gocyclo -avg .

.link http://github.com/alecthomas/gocyclo

* goimports

Command goimports updates your Go import lines, adding missing ones and removing unreferenced ones.

Most editors have this built in.  Highly recommended to keep you sane.

.link http://golang.org/x/tools/cmd/goimports

* gosimple

Gosimple is a linter for Go source code that specialises on simplifying code.

	go get -u honnef.co/go/simple/cmd/gosimple

Usage

Invoke gosimple with one or more filenames, a directory, or a package named by
its import path. Gosimple uses the same import path syntax as the go command
and therefore also supports relative import paths like ./.... Additionally the ...
 wildcard can be used as suffix on relative and absolute file paths to
recurse into them.

The output of this tool is a list of suggestions in Vim quickfix format, which
is accepted by lots of different editors.

.link https://github.com/dominikh/go-simple

* ineffassign

Detect ineffectual assignments in Go code.

	go get -u github.com/gordonklaus/ineffassign
	ineffassign ./..

.link http://github.com/gordonklaus/ineffassign

* interfacer

A linter that suggests interface types. In other words, it warns about the
usage of types that are more specific than necessary.

	go get -u github.com/mvdan/interfacer/cmd/interfacer
	interfacer ./...

.link http://github.com/mvdan/interfacer

* lll

Line length linter, used to enforce line length in files. Support for only checking go files.

	go get -u github.com/walle/lll/...

Usage

	usage: lll [--maxlength MAXLENGTH] [--tabwidth TABWIDTH] [--goonly] [--skiplist SKIPLIST] [--vendor] [--files] [--exclude EXCLUDE] [INPUT [INPUT ...]]

.link http://github.com/walle/lll

* misspell

Correct commonly misspelled English words... quickly.

	go get -u github.com/client9/misspell/cmd/misspell
	find . -type f | xargs misspell

.link http://github.com/client9/misspell

* staticcheck

Staticcheck is go vet on steroids, applying a ton of static analysis checks you
might be used to from tools like ReSharper for C#.

	go get -u honnef.co/go/staticcheck/cmd/staticcheck
	staticcheck ./...

.link https://github.com/dominikh/go-staticcheck

* unconvert

The unconvert program analyzes Go packages to identify unnecessary type
conversions; i.e., expressions T(x) where x already has type T.

	go get -u github.com/mdempsky/unconvert

Usage:

    $ unconvert -v bytes fmt
    GOROOT/src/bytes/reader.go:117:14: unnecessary conversion
                    abs = int64(r.i) + offset
                               ^
    GOROOT/src/fmt/print.go:411:21: unnecessary conversion
            p.fmt.integer(int64(v), 16, unsigned, udigits)


.link http://github.com/mdempsky/unconvert

* unused

unused checks Go code for unused constants, variables, functions and types.

	go get -u honnef.co/go/unused/cmd/unused
	unused ./...

.link https://github.com/dominikh/go-unused

* Wow, that's a lot to remember...

* Go Meta Linter to the rescue!

Runs all of these commands against your code!

	go get -u github.com/alecthomas/gometalinter
	gometalinter.v1 --install
	gometalinter.v1 ./...

.link https://github.com/alecthomas/gometalinter

* Enforcement through git hooks

Place this script in `<reponame>/.git/hooks/pre-commit`

	fmtcount=`git ls-files | grep '.go$' | xargs gofmt -l 2>&1 | wc -l`
	if [ $fmtcount -gt 0 ]; then
	    echo "Some files aren't formatted, please run 'go fmt ./...' to format your source code before committing"
	    exit 1
	fi

	vetcount=`go tool vet ./ 2>&1  | wc -l`
	if [ $vetcount -gt 0 ]; then
	    echo "Some files aren't passing vet heuristics, please run 'go vet ./...' to see the errors it flags and correct your source code before committing"
	    exit 1
	fi
	exit 0