Cheatsheet

Fast one-page lookup: everyday Go syntax and idioms up top, then the verified build/test/CLI commands and directory layout of a real Go system — multigres (“Vitess for Postgres”) — below. Each row links into the language and project tracks for depth.

Go syntax

Declarations

Form	Example	Notes
var	var n int	zero value (0, "", nil)
:=	n := 42	short, function-scope only
const	const Max = 1 << 20	compile-time
iota	const ( A = iota; B; C )	0,1,2 enum counter
multi	a, b := 1, 2	tuple assign / swap a, b = b, a

Slices

s := make([]int, 0, 8)   // len 0, cap 8
s = append(s, 1, 2)      // grow (may realloc)
n := copy(dst, src)      // n = min(len(dst), len(src))
s = s[2:5]               // sub-slice (shares backing array)
clear(s)                 // zero all elements (Go 1.21+)

A sub-slice shares the backing array — appending into it can clobber the parent. See stdlib & idioms.

Maps

v, ok := m[k]    // comma-ok: ok=false if absent
delete(m, k)     // no-op if absent
for k, v := range m { ... }   // unordered
clear(m)         // remove all keys

Error pattern

if err != nil {
    return nil, fmt.Errorf("doing X: %w", err)  // wrap with %w
}

errors.Is(err, target) / errors.As(err, &t) to inspect. Depth: errors. In this codebase, errors at RPC/service boundaries use mterrors, not bare fmt.Errorf — see the mterrors section below.

Goroutine / channel / select

go work()                       // fire-and-forget goroutine
ch := make(chan int, 4)         // buffered (cap 4); unbuffered if no cap
ch <- v        // send
v, ok := <-ch  // receive; ok=false when closed and drained
close(ch)      // sender closes, never the receiver

select {
case v := <-ch:   ...
case ch2 <- x:    ...
case <-ctx.Done():  return ctx.Err()   // cancellation
default:          ...                  // non-blocking
}

Depth: concurrency.

Context

func Do(ctx context.Context, ...) error {   // ctx is always the FIRST param
    ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
    defer cancel()                           // always defer cancel
    ...
}

Depth: context.

Struct tags

type Config struct {
    Name string `json:"name"`
    Port int    `json:"port,omitempty"`
}

Backtick-quoted key:"value" metadata read by reflection (encoding, validation). Depth: stdlib & idioms.

Generics

func Map[T, U any](s []T, f func(T) U) []U { ... }
type Group[K comparable, V any] struct { ... }   // K must be comparable

any = interface{}; comparable = usable with ==. A real example: func NewGroup[K comparable, V any]() *Group[K, V] in the codebase’s singleflight cache. Depth: generics.

defer / recover

defer f()              // runs at function return, LIFO order
defer func() {
    if r := recover(); r != nil { ... }   // recover only inside a deferred func
}()

Deferred args are evaluated when defer runs, not when the function returns.

Real-world commands

The examples below come from multigres: Go 1.25, a single module github.com/multigres/multigres, all code under go/. The build is Makefile-driven; make help auto-generates the target list from ## comments — a tidy pattern worth borrowing.

Make targets

Target	Does
make tools	Install protobuf + build tools
make build	Build all 7 binaries into bin/ (debug, with symbols)
make build-release	Static, stripped release binaries (CGO_ENABLED=0)
make build-all	proto + parser + metrics + build
make proto	Regenerate protobuf into go/pb
make parser	go generate the SQL parser: goyacc and asthelpergen
make metrics	Generate the Prometheus metric catalog
make generate	Alias for parser + metrics (NOT proto)
make install	Install binaries to GOPATH/bin
make test	Run all tests (starts the port-pool server)
make test-short	Short tests only
make test-race	Tests with the race detector
make test-coverage	Comprehensive coverage
make clean / make clean-all	Remove build artifacts / + deps
make validate-generated-files	CI check: regenerate everything and diff
make pgregress / pgexternal / pgproto	PostgreSQL regression / external-ext / wire-protocol suites

The 7 binaries are multigateway, multipooler, pgctld, multiorch, multigres, multiadmin, and portpoolserver, each built via go build -o bin/$cmd ./go/cmd/$cmd.

Gotcha

After adding AST node types, run make build-all (not just make parser) so the AST code generator regenerates ast_clone.go/ast_rewrite.go — otherwise the validate-generated-files CI job fails. Depth: build & make, modules, deps & codegen.

Running tests

This codebase runs its tests through a dev wrapper rather than calling go test directly — integration runs need a shared port pool, or they collide flakily. The wrapper expands to ordinary go test invocations:

Invocation	Expands to
unit all	go test -short ./go/...
unit <pkg> [TestName]	go test [-run TestName] <pkg>
integration all	make build && go test ./go/test/endtoend/...
integration <pkg> [TestName]	make build + start port pool + go test [-run TestName] ./go/test/endtoend/<pkg>/...

Integration <pkg> values: all, multipooler, multiorch, queryserving, localprovisioner, shardsetup, pgregresstest. Common flags: -v -race -cover -count=N -short -timeout.

Note

Plain go test ./go/... also traverses go/test/endtoend/...; use -short for unit-only runs. Depth: testing workflow.

multigres CLI (local cluster)

The multigres binary doubles as the cluster-management CLI:

Command	Does
./bin/multigres cluster init	Initialize cluster config
./bin/multigres cluster start	Start local cluster components
./bin/multigres cluster stop [--clean]	Stop (--clean wipes state)
./bin/multigres cluster status	Show component status
./bin/multigres getpoolers	List registered poolers
./bin/multigres getpoolerstatus --cell <cell> --service-id <id>	Status of one pooler

Depth: cmd & cobra.

Errors — mterrors

Project error constructors (where code is a protobuf RPC code):

mterrors.New(code, message)
mterrors.Errorf(code, format, args...)
mterrors.Wrap(err, message)
mterrors.Wrapf(err, format, args...)
mterrors.NewPgError(...)   // Postgres wire errors

Use these at RPC/service boundaries; reserve stdlib fmt.Errorf("...: %w", err) for internal wrapping. Depth: mterrors & observability.

Key directories

• Directorygo/

  • Directorycmd/ entrypoints for the 7 binaries

    • …
  • Directoryservices/ service impls: multiadmin, multigateway, multiorch, multipooler, pgctld

    • …
  • Directorycommon/ shared libs: mterrors, parser, pgprotocol, sqltypes, consensus, servenv, …

    • …
  • Directorypb/ generated protobuf (output of make proto)

    • …
  • Directoryobservability/ generated metric catalog (output of make metrics)

    • …
  • Directorytest/endtoend/ integration tests

    • …
• Directoryproto/ proto source files

  • …

See also

• Orientation
• Glossary — terms
• Idioms and gotchas
• Further reading
• Language: errors, generics, concurrency, context, stdlib & idioms
• Project: cmd & cobra, grpc & protobuf, mterrors & observability
• Tooling: build & make, testing workflow, modules, deps & codegen