| // 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 build gathers information about Go packages. |
| // |
| // Go Path |
| // |
| // The Go path is a list of directory trees containing Go source code. |
| // It is consulted to resolve imports that cannot be found in the standard |
| // Go tree. The default path is the value of the GOPATH environment |
| // variable, interpreted as a path list appropriate to the operating system |
| // (on Unix, the variable is a colon-separated string; |
| // on Windows, a semicolon-separated string; |
| // on Plan 9, a list). |
| // |
| // Each directory listed in the Go path must have a prescribed structure: |
| // |
| // The src/ directory holds source code. The path below 'src' determines |
| // the import path or executable name. |
| // |
| // The pkg/ directory holds installed package objects. |
| // As in the Go tree, each target operating system and |
| // architecture pair has its own subdirectory of pkg |
| // (pkg/GOOS_GOARCH). |
| // |
| // If DIR is a directory listed in the Go path, a package with |
| // source in DIR/src/foo/bar can be imported as "foo/bar" and |
| // has its compiled form installed to "DIR/pkg/GOOS_GOARCH/foo/bar.a" |
| // (or, for gccgo, "DIR/pkg/gccgo/foo/libbar.a"). |
| // |
| // The bin/ directory holds compiled commands. |
| // Each command is named for its source directory, but only |
| // using the final element, not the entire path. That is, the |
| // command with source in DIR/src/foo/quux is installed into |
| // DIR/bin/quux, not DIR/bin/foo/quux. The foo/ is stripped |
| // so that you can add DIR/bin to your PATH to get at the |
| // installed commands. |
| // |
| // Here's an example directory layout: |
| // |
| // GOPATH=/home/user/gocode |
| // |
| // /home/user/gocode/ |
| // src/ |
| // foo/ |
| // bar/ (go code in package bar) |
| // x.go |
| // quux/ (go code in package main) |
| // y.go |
| // bin/ |
| // quux (installed command) |
| // pkg/ |
| // linux_amd64/ |
| // foo/ |
| // bar.a (installed package object) |
| // |
| // Build Constraints |
| // |
| // A build constraint, also known as a build tag, is a line comment that begins |
| // |
| // // +build |
| // |
| // that lists the conditions under which a file should be included in the package. |
| // Constraints may appear in any kind of source file (not just Go), but |
| // they must appear near the top of the file, preceded |
| // only by blank lines and other line comments. These rules mean that in Go |
| // files a build constraint must appear before the package clause. |
| // |
| // To distinguish build constraints from package documentation, a series of |
| // build constraints must be followed by a blank line. |
| // |
| // A build constraint is evaluated as the OR of space-separated options; |
| // each option evaluates as the AND of its comma-separated terms; |
| // and each term is an alphanumeric word or, preceded by !, its negation. |
| // That is, the build constraint: |
| // |
| // // +build linux,386 darwin,!cgo |
| // |
| // corresponds to the boolean formula: |
| // |
| // (linux AND 386) OR (darwin AND (NOT cgo)) |
| // |
| // A file may have multiple build constraints. The overall constraint is the AND |
| // of the individual constraints. That is, the build constraints: |
| // |
| // // +build linux darwin |
| // // +build 386 |
| // |
| // corresponds to the boolean formula: |
| // |
| // (linux OR darwin) AND 386 |
| // |
| // During a particular build, the following words are satisfied: |
| // |
| // - the target operating system, as spelled by runtime.GOOS |
| // - the target architecture, as spelled by runtime.GOARCH |
| // - the compiler being used, either "gc" or "gccgo" |
| // - "cgo", if ctxt.CgoEnabled is true |
| // - "go1.1", from Go version 1.1 onward |
| // - "go1.2", from Go version 1.2 onward |
| // - "go1.3", from Go version 1.3 onward |
| // - "go1.4", from Go version 1.4 onward |
| // - "go1.5", from Go version 1.5 onward |
| // - any additional words listed in ctxt.BuildTags |
| // |
| // If a file's name, after stripping the extension and a possible _test suffix, |
| // matches any of the following patterns: |
| // *_GOOS |
| // *_GOARCH |
| // *_GOOS_GOARCH |
| // (example: source_windows_amd64.go) where GOOS and GOARCH represent |
| // any known operating system and architecture values respectively, then |
| // the file is considered to have an implicit build constraint requiring |
| // those terms (in addition to any explicit constraints in the file). |
| // |
| // To keep a file from being considered for the build: |
| // |
| // // +build ignore |
| // |
| // (any other unsatisfied word will work as well, but ``ignore'' is conventional.) |
| // |
| // To build a file only when using cgo, and only on Linux and OS X: |
| // |
| // // +build linux,cgo darwin,cgo |
| // |
| // Such a file is usually paired with another file implementing the |
| // default functionality for other systems, which in this case would |
| // carry the constraint: |
| // |
| // // +build !linux,!darwin !cgo |
| // |
| // Naming a file dns_windows.go will cause it to be included only when |
| // building the package for Windows; similarly, math_386.s will be included |
| // only when building the package for 32-bit x86. |
| // |
| // Using GOOS=android matches build tags and files as for GOOS=linux |
| // in addition to android tags and files. |
| // |
| package build |
