cmd/dist: implement //go:build parsing
The bootstrap directories are built with the Go 1.4 go command,
and they will retain the // +build lines until we bump the bootstrap
toolchain to Go 1.17 or later.
cmd/dist builds cmd/go and all its dependencies, using the
assembler, compiler, and linker that were built using Go 1.4.
We don't want to have to keep // +build lines in cmd/go and
all its dependencies, so this CL changes cmd/dist to understand
the //go:build lines.
cmd/dist is a standalone Go program that must itself build with
very old Go releases, so we cannot assume go/build/constraint
is available. Instead, implement a trivial parser/evaluator.
For #41184.
Change-Id: I84e259dec3bd3daec3f82024eb3500120f53096d
Reviewed-on: https://go-review.googlesource.com/c/go/+/359314
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 39f016e..d37c3f8 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -812,6 +812,9 @@
importMap := make(map[string]string)
for _, p := range gofiles {
for _, imp := range readimports(p) {
+ if imp == "C" {
+ fatalf("%s imports C", p)
+ }
importMap[imp] = resolveVendor(imp, dir)
}
}
@@ -822,6 +825,9 @@
sort.Strings(sortedImports)
for _, dep := range importMap {
+ if dep == "C" {
+ fatalf("%s imports C", pkg)
+ }
startInstall(dep)
}
for _, dep := range importMap {
@@ -970,28 +976,8 @@
return pathf("%s/pkg/%s_%s/%s.a", goroot, goos, goarch, pkg)
}
-// matchfield reports whether the field (x,y,z) matches this build.
-// all the elements in the field must be satisfied.
-func matchfield(f string) bool {
- for _, tag := range strings.Split(f, ",") {
- if !matchtag(tag) {
- return false
- }
- }
- return true
-}
-
-// matchtag reports whether the tag (x or !x) matches this build.
+// matchtag reports whether the tag matches this build.
func matchtag(tag string) bool {
- if tag == "" {
- return false
- }
- if tag[0] == '!' {
- if len(tag) == 1 || tag[1] == '!' {
- return false
- }
- return !matchtag(tag[1:])
- }
return tag == "gc" || tag == goos || tag == goarch || tag == "cmd_go_bootstrap" || tag == "go1.1" ||
(goos == "android" && tag == "linux") ||
(goos == "illumos" && tag == "solaris") ||
@@ -1032,7 +1018,7 @@
return false
}
- // Check file contents for // +build lines.
+ // Check file contents for //go:build lines.
for _, p := range strings.Split(readfile(file), "\n") {
p = strings.TrimSpace(p)
if p == "" {
@@ -1052,20 +1038,13 @@
if !strings.HasPrefix(p, "//") {
break
}
- if !strings.Contains(p, "+build") {
- continue
- }
- fields := strings.Fields(p[2:])
- if len(fields) < 1 || fields[0] != "+build" {
- continue
- }
- for _, p := range fields[1:] {
- if matchfield(p) {
- goto fieldmatch
+ if strings.HasPrefix(p, "//go:build ") {
+ matched, err := matchexpr(p[len("//go:build "):])
+ if err != nil {
+ errprintf("%s: %v", file, err)
}
+ return matched
}
- return false
- fieldmatch:
}
return true
diff --git a/src/cmd/dist/buildtag.go b/src/cmd/dist/buildtag.go
new file mode 100644
index 0000000..24776a0
--- /dev/null
+++ b/src/cmd/dist/buildtag.go
@@ -0,0 +1,133 @@
+// Copyright 2021 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 main
+
+import (
+ "fmt"
+ "strings"
+)
+
+// exprParser is a //go:build expression parser and evaluator.
+// The parser is a trivial precedence-based parser which is still
+// almost overkill for these very simple expressions.
+type exprParser struct {
+ x string
+ t exprToken // upcoming token
+}
+
+// val is the value type result of parsing.
+// We don't keep a parse tree, just the value of the expression.
+type val bool
+
+// exprToken describes a single token in the input.
+// Prefix operators define a prefix func that parses the
+// upcoming value. Binary operators define an infix func
+// that combines two values according to the operator.
+// In that case, the parsing loop parses the two values.
+type exprToken struct {
+ tok string
+ prec int
+ prefix func(*exprParser) val
+ infix func(val, val) val
+}
+
+var exprTokens []exprToken
+
+func init() { // init to break init cycle
+ exprTokens = []exprToken{
+ {tok: "&&", prec: 1, infix: func(x, y val) val { return x && y }},
+ {tok: "||", prec: 2, infix: func(x, y val) val { return x || y }},
+ {tok: "!", prec: 3, prefix: (*exprParser).not},
+ {tok: "(", prec: 3, prefix: (*exprParser).paren},
+ {tok: ")"},
+ }
+}
+
+// matchexpr parses and evaluates the //go:build expression x.
+func matchexpr(x string) (matched bool, err error) {
+ defer func() {
+ if e := recover(); e != nil {
+ matched = false
+ err = fmt.Errorf("parsing //go:build line: %v", e)
+ }
+ }()
+
+ p := &exprParser{x: x}
+ p.next()
+ v := p.parse(0)
+ if p.t.tok != "end of expression" {
+ panic("unexpected " + p.t.tok)
+ }
+ return bool(v), nil
+}
+
+// parse parses an expression, including binary operators at precedence >= prec.
+func (p *exprParser) parse(prec int) val {
+ if p.t.prefix == nil {
+ panic("unexpected " + p.t.tok)
+ }
+ v := p.t.prefix(p)
+ for p.t.prec >= prec && p.t.infix != nil {
+ t := p.t
+ p.next()
+ v = t.infix(v, p.parse(t.prec+1))
+ }
+ return v
+}
+
+// not is the prefix parser for a ! token.
+func (p *exprParser) not() val {
+ p.next()
+ return !p.parse(100)
+}
+
+// paren is the prefix parser for a ( token.
+func (p *exprParser) paren() val {
+ p.next()
+ v := p.parse(0)
+ if p.t.tok != ")" {
+ panic("missing )")
+ }
+ p.next()
+ return v
+}
+
+// next advances the parser to the next token,
+// leaving the token in p.t.
+func (p *exprParser) next() {
+ p.x = strings.TrimSpace(p.x)
+ if p.x == "" {
+ p.t = exprToken{tok: "end of expression"}
+ return
+ }
+ for _, t := range exprTokens {
+ if strings.HasPrefix(p.x, t.tok) {
+ p.x = p.x[len(t.tok):]
+ p.t = t
+ return
+ }
+ }
+
+ i := 0
+ for i < len(p.x) && validtag(p.x[i]) {
+ i++
+ }
+ if i == 0 {
+ panic(fmt.Sprintf("syntax error near %#q", rune(p.x[i])))
+ }
+ tag := p.x[:i]
+ p.x = p.x[i:]
+ p.t = exprToken{
+ tok: "tag",
+ prefix: func(p *exprParser) val {
+ p.next()
+ return val(matchtag(tag))
+ },
+ }
+}
+
+func validtag(c byte) bool {
+ return 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' || c == '.' || c == '_'
+}
