Source file src/pkg/go/build/doc.go
1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package build gathers information about Go packages. 6 // 7 // Go Path 8 // 9 // The Go path is a list of directory trees containing Go source code. 10 // It is consulted to resolve imports that cannot be found in the standard 11 // Go tree. The default path is the value of the GOPATH environment 12 // variable, interpreted as a path list appropriate to the operating system 13 // (on Unix, the variable is a colon-separated string; 14 // on Windows, a semicolon-separated string; 15 // on Plan 9, a list). 16 // 17 // Each directory listed in the Go path must have a prescribed structure: 18 // 19 // The src/ directory holds source code. The path below 'src' determines 20 // the import path or executable name. 21 // 22 // The pkg/ directory holds installed package objects. 23 // As in the Go tree, each target operating system and 24 // architecture pair has its own subdirectory of pkg 25 // (pkg/GOOS_GOARCH). 26 // 27 // If DIR is a directory listed in the Go path, a package with 28 // source in DIR/src/foo/bar can be imported as "foo/bar" and 29 // has its compiled form installed to "DIR/pkg/GOOS_GOARCH/foo/bar.a" 30 // (or, for gccgo, "DIR/pkg/gccgo/foo/libbar.a"). 31 // 32 // The bin/ directory holds compiled commands. 33 // Each command is named for its source directory, but only 34 // using the final element, not the entire path. That is, the 35 // command with source in DIR/src/foo/quux is installed into 36 // DIR/bin/quux, not DIR/bin/foo/quux. The foo/ is stripped 37 // so that you can add DIR/bin to your PATH to get at the 38 // installed commands. 39 // 40 // Here's an example directory layout: 41 // 42 // GOPATH=/home/user/gocode 43 // 44 // /home/user/gocode/ 45 // src/ 46 // foo/ 47 // bar/ (go code in package bar) 48 // x.go 49 // quux/ (go code in package main) 50 // y.go 51 // bin/ 52 // quux (installed command) 53 // pkg/ 54 // linux_amd64/ 55 // foo/ 56 // bar.a (installed package object) 57 // 58 // Build Constraints 59 // 60 // A build constraint is a line comment beginning with the directive +build 61 // that lists the conditions under which a file should be included in the package. 62 // Constraints may appear in any kind of source file (not just Go), but 63 // they must be appear near the top of the file, preceded 64 // only by blank lines and other line comments. 65 // 66 // A build constraint is evaluated as the OR of space-separated options; 67 // each option evaluates as the AND of its comma-separated terms; 68 // and each term is an alphanumeric word or, preceded by !, its negation. 69 // That is, the build constraint: 70 // 71 // // +build linux,386 darwin,!cgo 72 // 73 // corresponds to the boolean formula: 74 // 75 // (linux AND 386) OR (darwin AND (NOT cgo)) 76 // 77 // During a particular build, the following words are satisfied: 78 // 79 // - the target operating system, as spelled by runtime.GOOS 80 // - the target architecture, as spelled by runtime.GOARCH 81 // - "cgo", if ctxt.CgoEnabled is true 82 // - any additional words listed in ctxt.BuildTags 83 // 84 // If a file's name, after stripping the extension and a possible _test suffix, 85 // matches *_GOOS, *_GOARCH, or *_GOOS_GOARCH for any known operating 86 // system and architecture values, then the file is considered to have an implicit 87 // build constraint requiring those terms. 88 // 89 // To keep a file from being considered for the build: 90 // 91 // // +build ignore 92 // 93 // (any other unsatisfied word will work as well, but ``ignore'' is conventional.) 94 // 95 // To build a file only when using cgo, and only on Linux and OS X: 96 // 97 // // +build linux,cgo darwin,cgo 98 // 99 // Such a file is usually paired with another file implementing the 100 // default functionality for other systems, which in this case would 101 // carry the constraint: 102 // 103 // // +build !linux !darwin !cgo 104 // 105 // Naming a file dns_windows.go will cause it to be included only when 106 // building the package for Windows; similarly, math_386.s will be included 107 // only when building the package for 32-bit x86. 108 // 109 package build