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, also known as a build tag, is a line comment that begins 61 // 62 // // +build 63 // 64 // that lists the conditions under which a file should be included in the package. 65 // Constraints may appear in any kind of source file (not just Go), but 66 // they must appear near the top of the file, preceded 67 // only by blank lines and other line comments. These rules mean that in Go 68 // files a build constraint must appear before the package clause. 69 // 70 // To distinguish build constraints from package documentation, a series of 71 // build constraints must be followed by a blank line. 72 // 73 // A build constraint is evaluated as the OR of space-separated options; 74 // each option evaluates as the AND of its comma-separated terms; 75 // and each term is an alphanumeric word or, preceded by !, its negation. 76 // That is, the build constraint: 77 // 78 // // +build linux,386 darwin,!cgo 79 // 80 // corresponds to the boolean formula: 81 // 82 // (linux AND 386) OR (darwin AND (NOT cgo)) 83 // 84 // A file may have multiple build constraints. The overall constraint is the AND 85 // of the individual constraints. That is, the build constraints: 86 // 87 // // +build linux darwin 88 // // +build 386 89 // 90 // corresponds to the boolean formula: 91 // 92 // (linux OR darwin) AND 386 93 // 94 // During a particular build, the following words are satisfied: 95 // 96 // - the target operating system, as spelled by runtime.GOOS 97 // - the target architecture, as spelled by runtime.GOARCH 98 // - the compiler being used, either "gc" or "gccgo" 99 // - "cgo", if ctxt.CgoEnabled is true 100 // - "go1.1", from Go version 1.1 onward 101 // - "go1.2", from Go version 1.2 onward 102 // - "go1.3", from Go version 1.3 onward 103 // - "go1.4", from Go version 1.4 onward 104 // - "go1.5", from Go version 1.5 onward 105 // - "go1.6", from Go version 1.6 onward 106 // - "go1.7", from Go version 1.7 onward 107 // - "go1.8", from Go version 1.8 onward 108 // - "go1.9", from Go version 1.9 onward 109 // - "go1.10", from Go version 1.10 onward 110 // - any additional words listed in ctxt.BuildTags 111 // 112 // If a file's name, after stripping the extension and a possible _test suffix, 113 // matches any of the following patterns: 114 // *_GOOS 115 // *_GOARCH 116 // *_GOOS_GOARCH 117 // (example: source_windows_amd64.go) where GOOS and GOARCH represent 118 // any known operating system and architecture values respectively, then 119 // the file is considered to have an implicit build constraint requiring 120 // those terms (in addition to any explicit constraints in the file). 121 // 122 // To keep a file from being considered for the build: 123 // 124 // // +build ignore 125 // 126 // (any other unsatisfied word will work as well, but ``ignore'' is conventional.) 127 // 128 // To build a file only when using cgo, and only on Linux and OS X: 129 // 130 // // +build linux,cgo darwin,cgo 131 // 132 // Such a file is usually paired with another file implementing the 133 // default functionality for other systems, which in this case would 134 // carry the constraint: 135 // 136 // // +build !linux,!darwin !cgo 137 // 138 // Naming a file dns_windows.go will cause it to be included only when 139 // building the package for Windows; similarly, math_386.s will be included 140 // only when building the package for 32-bit x86. 141 // 142 // Using GOOS=android matches build tags and files as for GOOS=linux 143 // in addition to android tags and files. 144 // 145 // Binary-Only Packages 146 // 147 // It is possible to distribute packages in binary form without including the 148 // source code used for compiling the package. To do this, the package must 149 // be distributed with a source file not excluded by build constraints and 150 // containing a "//go:binary-only-package" comment. 151 // Like a build constraint, this comment must appear near the top of the file, 152 // preceded only by blank lines and other line comments and with a blank line 153 // following the comment, to separate it from the package documentation. 154 // Unlike build constraints, this comment is only recognized in non-test 155 // Go source files. 156 // 157 // The minimal source code for a binary-only package is therefore: 158 // 159 // //go:binary-only-package 160 // 161 // package mypkg 162 // 163 // The source code may include additional Go code. That code is never compiled 164 // but will be processed by tools like godoc and might be useful as end-user 165 // documentation. 166 // 167 package build 168
