1 files changed, 251 insertions, 0 deletions
diff --git a/src/cmd/go/internal/imports/build.go b/src/cmd/go/internal/imports/build.go
new file mode 100644
index 0000000..50aeabc
--- /dev/null
+++ b/src/cmd/go/internal/imports/build.go
@@ -0,0 +1,251 @@
+// Copyright 2018 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.
+
+// Copied from Go distribution src/go/build/build.go, syslist.go
+
+package imports
+
+import (
+	"bytes"
+	"strings"
+	"unicode"
+)
+
+var slashslash = []byte("//")
+
+// ShouldBuild reports whether it is okay to use this file,
+// The rule is that in the file's leading run of // comments
+// and blank lines, which must be followed by a blank line
+// (to avoid including a Go package clause doc comment),
+// lines beginning with '// +build' are taken as build directives.
+//
+// The file is accepted only if each such line lists something
+// matching the file. For example:
+//
+//	// +build windows linux
+//
+// marks the file as applicable only on Windows and Linux.
+//
+// If tags["*"] is true, then ShouldBuild will consider every
+// build tag except "ignore" to be both true and false for
+// the purpose of satisfying build tags, in order to estimate
+// (conservatively) whether a file could ever possibly be used
+// in any build.
+//
+func ShouldBuild(content []byte, tags map[string]bool) bool {
+	// Pass 1. Identify leading run of // comments and blank lines,
+	// which must be followed by a blank line.
+	end := 0
+	p := content
+	for len(p) > 0 {
+		line := p
+		if i := bytes.IndexByte(line, '\n'); i >= 0 {
+			line, p = line[:i], p[i+1:]
+		} else {
+			p = p[len(p):]
+		}
+		line = bytes.TrimSpace(line)
+		if len(line) == 0 { // Blank line
+			end = len(content) - len(p)
+			continue
+		}
+		if !bytes.HasPrefix(line, slashslash) { // Not comment line
+			break
+		}
+	}
+	content = content[:end]
+
+	// Pass 2.  Process each line in the run.
+	p = content
+	allok := true
+	for len(p) > 0 {
+		line := p
+		if i := bytes.IndexByte(line, '\n'); i >= 0 {
+			line, p = line[:i], p[i+1:]
+		} else {
+			p = p[len(p):]
+		}
+		line = bytes.TrimSpace(line)
+		if !bytes.HasPrefix(line, slashslash) {
+			continue
+		}
+		line = bytes.TrimSpace(line[len(slashslash):])
+		if len(line) > 0 && line[0] == '+' {
+			// Looks like a comment +line.
+			f := strings.Fields(string(line))
+			if f[0] == "+build" {
+				ok := false
+				for _, tok := range f[1:] {
+					if matchTags(tok, tags) {
+						ok = true
+					}
+				}
+				if !ok {
+					allok = false
+				}
+			}
+		}
+	}
+
+	return allok
+}
+
+// matchTags reports whether the name is one of:
+//
+//	tag (if tags[tag] is true)
+//	!tag (if tags[tag] is false)
+//	a comma-separated list of any of these
+//
+func matchTags(name string, tags map[string]bool) bool {
+	if name == "" {
+		return false
+	}
+	if i := strings.Index(name, ","); i >= 0 {
+		// comma-separated list
+		ok1 := matchTags(name[:i], tags)
+		ok2 := matchTags(name[i+1:], tags)
+		return ok1 && ok2
+	}
+	if strings.HasPrefix(name, "!!") { // bad syntax, reject always
+		return false
+	}
+	if strings.HasPrefix(name, "!") { // negation
+		return len(name) > 1 && matchTag(name[1:], tags, false)
+	}
+	return matchTag(name, tags, true)
+}
+
+// matchTag reports whether the tag name is valid and satisfied by tags[name]==want.
+func matchTag(name string, tags map[string]bool, want bool) bool {
+	// Tags must be letters, digits, underscores or dots.
+	// Unlike in Go identifiers, all digits are fine (e.g., "386").
+	for _, c := range name {
+		if !unicode.IsLetter(c) && !unicode.IsDigit(c) && c != '_' && c != '.' {
+			return false
+		}
+	}
+
+	if tags["*"] && name != "" && name != "ignore" {
+		// Special case for gathering all possible imports:
+		// if we put * in the tags map then all tags
+		// except "ignore" are considered both present and not
+		// (so we return true no matter how 'want' is set).
+		return true
+	}
+
+	have := tags[name]
+	if name == "linux" {
+		have = have || tags["android"]
+	}
+	if name == "solaris" {
+		have = have || tags["illumos"]
+	}
+	if name == "darwin" {
+		have = have || tags["ios"]
+	}
+	return have == want
+}
+
+// MatchFile returns false if the name contains a $GOOS or $GOARCH
+// suffix which does not match the current system.
+// The recognized name formats are:
+//
+//     name_$(GOOS).*
+//     name_$(GOARCH).*
+//     name_$(GOOS)_$(GOARCH).*
+//     name_$(GOOS)_test.*
+//     name_$(GOARCH)_test.*
+//     name_$(GOOS)_$(GOARCH)_test.*
+//
+// Exceptions:
+//     if GOOS=android, then files with GOOS=linux are also matched.
+//     if GOOS=illumos, then files with GOOS=solaris are also matched.
+//     if GOOS=ios, then files with GOOS=darwin are also matched.
+//
+// If tags["*"] is true, then MatchFile will consider all possible
+// GOOS and GOARCH to be available and will consequently
+// always return true.
+func MatchFile(name string, tags map[string]bool) bool {
+	if tags["*"] {
+		return true
+	}
+	if dot := strings.Index(name, "."); dot != -1 {
+		name = name[:dot]
+	}
+
+	// Before Go 1.4, a file called "linux.go" would be equivalent to having a
+	// build tag "linux" in that file. For Go 1.4 and beyond, we require this
+	// auto-tagging to apply only to files with a non-empty prefix, so
+	// "foo_linux.go" is tagged but "linux.go" is not. This allows new operating
+	// systems, such as android, to arrive without breaking existing code with
+	// innocuous source code in "android.go". The easiest fix: cut everything
+	// in the name before the initial _.
+	i := strings.Index(name, "_")
+	if i < 0 {
+		return true
+	}
+	name = name[i:] // ignore everything before first _
+
+	l := strings.Split(name, "_")
+	if n := len(l); n > 0 && l[n-1] == "test" {
+		l = l[:n-1]
+	}
+	n := len(l)
+	if n >= 2 && KnownOS[l[n-2]] && KnownArch[l[n-1]] {
+		return matchTag(l[n-2], tags, true) && matchTag(l[n-1], tags, true)
+	}
+	if n >= 1 && KnownOS[l[n-1]] {
+		return matchTag(l[n-1], tags, true)
+	}
+	if n >= 1 && KnownArch[l[n-1]] {
+		return matchTag(l[n-1], tags, true)
+	}
+	return true
+}
+
+var KnownOS = map[string]bool{
+	"aix":       true,
+	"android":   true,
+	"darwin":    true,
+	"dragonfly": true,
+	"freebsd":   true,
+	"hurd":      true,
+	"illumos":   true,
+	"ios":       true,
+	"js":        true,
+	"linux":     true,
+	"nacl":      true, // legacy; don't remove
+	"netbsd":    true,
+	"openbsd":   true,
+	"plan9":     true,
+	"solaris":   true,
+	"windows":   true,
+	"zos":       true,
+}
+
+var KnownArch = map[string]bool{
+	"386":         true,
+	"amd64":       true,
+	"amd64p32":    true, // legacy; don't remove
+	"arm":         true,
+	"armbe":       true,
+	"arm64":       true,
+	"arm64be":     true,
+	"ppc64":       true,
+	"ppc64le":     true,
+	"mips":        true,
+	"mipsle":      true,
+	"mips64":      true,
+	"mips64le":    true,
+	"mips64p32":   true,
+	"mips64p32le": true,
+	"ppc":         true,
+	"riscv":       true,
+	"riscv64":     true,
+	"s390":        true,
+	"s390x":       true,
+	"sparc":       true,
+	"sparc64":     true,
+	"wasm":        true,
+}