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go/build/constraint: add GoVersion

For #57001, programs need to be able to deduce the Go version
implied by a given build constraint. GoVersion determines that,
by discarding all build tags other than Go versions and computing
the minimum Go version implied by the resulting expression.

For #59033.

Change-Id: Ifb1e7af2bdbdf172f82aa490c826c9b6ca5e824b
Reviewed-on: https://go-review.googlesource.com/c/go/+/476275
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Russ Cox 2023-03-13 17:23:13 -04:00 committed by Gopher Robot
parent eb57c09054
commit 830f54b70e
4 changed files with 153 additions and 0 deletions

2
api/next/59033.txt Normal file
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@ -0,0 +1,2 @@
pkg go/build/constraint, func GoVersion(Expr) string #59033

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@ -59,6 +59,7 @@ var bootstrapDirs = []string{
"debug/elf",
"debug/macho",
"debug/pe",
"go/build/constraint",
"go/constant",
"internal/abi",
"internal/coverage",

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@ -0,0 +1,105 @@
// Copyright 2023 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 constraint
import (
"strconv"
"strings"
)
// GoVersion returns the minimum Go version implied by a given build expression.
// If the expression can be satisfied without any Go version tags, GoVersion returns an empty string.
//
// For example:
//
// GoVersion(linux && go1.22) = "go1.22"
// GoVersion((linux && go1.22) || (windows && go1.20)) = "go1.20" => go1.20
// GoVersion(linux) = ""
// GoVersion(linux || (windows && go1.22)) = ""
// GoVersion(!go1.22) = ""
//
// GoVersion assumes that any tag or negated tag may independently be true,
// so that its analysis can be purely structural, without SAT solving.
// “Impossible” subexpressions may therefore affect the result.
//
// For example:
//
// GoVersion((linux && !linux && go1.20) || go1.21) = "go1.20"
func GoVersion(x Expr) string {
v := minVersion(x, +1)
if v < 0 {
return ""
}
if v == 0 {
return "go1"
}
return "go1." + strconv.Itoa(v)
}
// minVersion returns the minimum Go major version (9 for go1.9)
// implied by expression z, or if sign < 0, by expression !z.
func minVersion(z Expr, sign int) int {
switch z := z.(type) {
default:
return -1
case *AndExpr:
op := andVersion
if sign < 0 {
op = orVersion
}
return op(minVersion(z.X, sign), minVersion(z.Y, sign))
case *OrExpr:
op := orVersion
if sign < 0 {
op = andVersion
}
return op(minVersion(z.X, sign), minVersion(z.Y, sign))
case *NotExpr:
return minVersion(z.X, -sign)
case *TagExpr:
if sign < 0 {
// !foo implies nothing
return -1
}
if z.Tag == "go1" {
return 0
}
_, v, _ := stringsCut(z.Tag, "go1.")
n, err := strconv.Atoi(v)
if err != nil {
// not a go1.N tag
return -1
}
return n
}
}
// TODO: Delete, replace calls with strings.Cut once Go bootstrap toolchain is bumped.
func stringsCut(s, sep string) (before, after string, found bool) {
if i := strings.Index(s, sep); i >= 0 {
return s[:i], s[i+len(sep):], true
}
return s, "", false
}
// andVersion returns the minimum Go version
// implied by the AND of two minimum Go versions,
// which is the max of the versions.
func andVersion(x, y int) int {
if x > y {
return x
}
return y
}
// orVersion returns the minimum Go version
// implied by the OR of two minimum Go versions,
// which is the min of the versions.
func orVersion(x, y int) int {
if x < y {
return x
}
return y
}

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@ -0,0 +1,45 @@
// Copyright 2023 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 constraint
import (
"fmt"
"testing"
)
var tests = []struct {
in string
out int
}{
{"//go:build linux && go1.60", 60},
{"//go:build ignore && go1.60", 60},
{"//go:build ignore || go1.60", -1},
{"//go:build go1.50 || (ignore && go1.60)", 50},
{"// +build go1.60,linux", 60},
{"// +build go1.60 linux", -1},
{"//go:build go1.50 && !go1.60", 50},
{"//go:build !go1.60", -1},
{"//go:build linux && go1.50 || darwin && go1.60", 50},
{"//go:build linux && go1.50 || !(!darwin || !go1.60)", 50},
}
func TestGoVersion(t *testing.T) {
for _, tt := range tests {
x, err := Parse(tt.in)
if err != nil {
t.Fatal(err)
}
v := GoVersion(x)
want := ""
if tt.out == 0 {
want = "go1"
} else if tt.out > 0 {
want = fmt.Sprintf("go1.%d", tt.out)
}
if v != want {
t.Errorf("GoVersion(%q) = %q, want %q, nil", tt.in, v, want)
}
}
}