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