path: root/src/cmd/go/internal/work/build.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package work

import (
	"errors"
	"fmt"
	"go/build"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"

	"cmd/go/internal/base"
	"cmd/go/internal/cfg"
	"cmd/go/internal/load"
	"cmd/go/internal/search"
)

var CmdBuild = &base.Command{
	UsageLine: "go build [-o output] [-i] [build flags] [packages]",
	Short:     "compile packages and dependencies",
	Long: `
Build compiles the packages named by the import paths,
along with their dependencies, but it does not install the results.

If the arguments to build are a list of .go files from a single directory,
build treats them as a list of source files specifying a single package.

When compiling packages, build ignores files that end in '_test.go'.

When compiling a single main package, build writes
the resulting executable to an output file named after
the first source file ('go build ed.go rx.go' writes 'ed' or 'ed.exe')
or the source code directory ('go build unix/sam' writes 'sam' or 'sam.exe').
The '.exe' suffix is added when writing a Windows executable.

When compiling multiple packages or a single non-main package,
build compiles the packages but discards the resulting object,
serving only as a check that the packages can be built.

The -o flag forces build to write the resulting executable or object
to the named output file or directory, instead of the default behavior described
in the last two paragraphs. If the named output is a directory that exists,
then any resulting executables will be written to that directory.

The -i flag installs the packages that are dependencies of the target.

The build flags are shared by the build, clean, get, install, list, run,
and test commands:

	-a
		force rebuilding of packages that are already up-to-date.
	-n
		print the commands but do not run them.
	-p n
		the number of programs, such as build commands or
		test binaries, that can be run in parallel.
		The default is the number of CPUs available.
	-race
		enable data race detection.
		Supported only on linux/amd64, freebsd/amd64, darwin/amd64, windows/amd64,
		linux/ppc64le and linux/arm64 (only for 48-bit VMA).
	-msan
		enable interoperation with memory sanitizer.
		Supported only on linux/amd64, linux/arm64
		and only with Clang/LLVM as the host C compiler.
		On linux/arm64, pie build mode will be used.
	-v
		print the names of packages as they are compiled.
	-work
		print the name of the temporary work directory and
		do not delete it when exiting.
	-x
		print the commands.

	-asmflags '[pattern=]arg list'
		arguments to pass on each go tool asm invocation.
	-buildmode mode
		build mode to use. See 'go help buildmode' for more.
	-compiler name
		name of compiler to use, as in runtime.Compiler (gccgo or gc).
	-gccgoflags '[pattern=]arg list'
		arguments to pass on each gccgo compiler/linker invocation.
	-gcflags '[pattern=]arg list'
		arguments to pass on each go tool compile invocation.
	-installsuffix suffix
		a suffix to use in the name of the package installation directory,
		in order to keep output separate from default builds.
		If using the -race flag, the install suffix is automatically set to race
		or, if set explicitly, has _race appended to it. Likewise for the -msan
		flag. Using a -buildmode option that requires non-default compile flags
		has a similar effect.
	-ldflags '[pattern=]arg list'
		arguments to pass on each go tool link invocation.
	-linkshared
		build code that will be linked against shared libraries previously
		created with -buildmode=shared.
	-mod mode
		module download mode to use: readonly, vendor, or mod.
		See 'go help modules' for more.
	-modcacherw
		leave newly-created directories in the module cache read-write
		instead of making them read-only.
	-modfile file
		in module aware mode, read (and possibly write) an alternate go.mod
		file instead of the one in the module root directory. A file named
		"go.mod" must still be present in order to determine the module root
		directory, but it is not accessed. When -modfile is specified, an
		alternate go.sum file is also used: its path is derived from the
		-modfile flag by trimming the ".mod" extension and appending ".sum".
	-pkgdir dir
		install and load all packages from dir instead of the usual locations.
		For example, when building with a non-standard configuration,
		use -pkgdir to keep generated packages in a separate location.
	-tags tag,list
		a comma-separated list of build tags to consider satisfied during the
		build. For more information about build tags, see the description of
		build constraints in the documentation for the go/build package.
		(Earlier versions of Go used a space-separated list, and that form
		is deprecated but still recognized.)
	-trimpath
		remove all file system paths from the resulting executable.
		Instead of absolute file system paths, the recorded file names
		will begin with either "go" (for the standard library),
		or a module path@version (when using modules),
		or a plain import path (when using GOPATH).
	-toolexec 'cmd args'
		a program to use to invoke toolchain programs like vet and asm.
		For example, instead of running asm, the go command will run
		'cmd args /path/to/asm <arguments for asm>'.

The -asmflags, -gccgoflags, -gcflags, and -ldflags flags accept a
space-separated list of arguments to pass to an underlying tool
during the build. To embed spaces in an element in the list, surround
it with either single or double quotes. The argument list may be
preceded by a package pattern and an equal sign, which restricts
the use of that argument list to the building of packages matching
that pattern (see 'go help packages' for a description of package
patterns). Without a pattern, the argument list applies only to the
packages named on the command line. The flags may be repeated
with different patterns in order to specify different arguments for
different sets of packages. If a package matches patterns given in
multiple flags, the latest match on the command line wins.
For example, 'go build -gcflags=-S fmt' prints the disassembly
only for package fmt, while 'go build -gcflags=all=-S fmt'
prints the disassembly for fmt and all its dependencies.

For more about specifying packages, see 'go help packages'.
For more about where packages and binaries are installed,
run 'go help gopath'.
For more about calling between Go and C/C++, run 'go help c'.

Note: Build adheres to certain conventions such as those described
by 'go help gopath'. Not all projects can follow these conventions,
however. Installations that have their own conventions or that use
a separate software build system may choose to use lower-level
invocations such as 'go tool compile' and 'go tool link' to avoid
some of the overheads and design decisions of the build tool.

See also: go install, go get, go clean.
	`,
}

const concurrentGCBackendCompilationEnabledByDefault = true

func init() {
	// break init cycle
	CmdBuild.Run = runBuild
	CmdInstall.Run = runInstall

	CmdBuild.Flag.BoolVar(&cfg.BuildI, "i", false, "")
	CmdBuild.Flag.StringVar(&cfg.BuildO, "o", "", "output file or directory")

	CmdInstall.Flag.BoolVar(&cfg.BuildI, "i", false, "")

	AddBuildFlags(CmdBuild, DefaultBuildFlags)
	AddBuildFlags(CmdInstall, DefaultBuildFlags)
}

// Note that flags consulted by other parts of the code
// (for example, buildV) are in cmd/go/internal/cfg.

var (
	forcedAsmflags   []string // internally-forced flags for cmd/asm
	forcedGcflags    []string // internally-forced flags for cmd/compile
	forcedLdflags    []string // internally-forced flags for cmd/link
	forcedGccgoflags []string // internally-forced flags for gccgo
)

var BuildToolchain toolchain = noToolchain{}
var ldBuildmode string

// buildCompiler implements flag.Var.
// It implements Set by updating both
// BuildToolchain and buildContext.Compiler.
type buildCompiler struct{}

func (c buildCompiler) Set(value string) error {
	switch value {
	case "gc":
		BuildToolchain = gcToolchain{}
	case "gccgo":
		BuildToolchain = gccgoToolchain{}
	default:
		return fmt.Errorf("unknown compiler %q", value)
	}
	cfg.BuildToolchainName = value
	cfg.BuildToolchainCompiler = BuildToolchain.compiler
	cfg.BuildToolchainLinker = BuildToolchain.linker
	cfg.BuildContext.Compiler = value
	return nil
}

func (c buildCompiler) String() string {
	return cfg.BuildContext.Compiler
}

func init() {
	switch build.Default.Compiler {
	case "gc", "gccgo":
		buildCompiler{}.Set(build.Default.Compiler)
	}
}

type BuildFlagMask int

const (
	DefaultBuildFlags BuildFlagMask = 0
	OmitModFlag       BuildFlagMask = 1 << iota
	OmitModCommonFlags
	OmitVFlag
)

// AddBuildFlags adds the flags common to the build, clean, get,
// install, list, run, and test commands.
func AddBuildFlags(cmd *base.Command, mask BuildFlagMask) {
	cmd.Flag.BoolVar(&cfg.BuildA, "a", false, "")
	cmd.Flag.BoolVar(&cfg.BuildN, "n", false, "")
	cmd.Flag.IntVar(&cfg.BuildP, "p", cfg.BuildP, "")
	if mask&OmitVFlag == 0 {
		cmd.Flag.BoolVar(&cfg.BuildV, "v", false, "")
	}
	cmd.Flag.BoolVar(&cfg.BuildX, "x", false, "")

	cmd.Flag.Var(&load.BuildAsmflags, "asmflags", "")
	cmd.Flag.Var(buildCompiler{}, "compiler", "")
	cmd.Flag.StringVar(&cfg.BuildBuildmode, "buildmode", "default", "")
	cmd.Flag.Var(&load.BuildGcflags, "gcflags", "")
	cmd.Flag.Var(&load.BuildGccgoflags, "gccgoflags", "")
	if mask&OmitModFlag == 0 {
		cmd.Flag.StringVar(&cfg.BuildMod, "mod", "", "")
	}
	if mask&OmitModCommonFlags == 0 {
		AddModCommonFlags(cmd)
	}
	cmd.Flag.StringVar(&cfg.BuildContext.InstallSuffix, "installsuffix", "", "")