interp/build: improve Go version handling.

.golangci.toml

@@ -44,7 +44,6 @@
     path = "cmd/goexports/goexports.go"
     text = "SA1019: importer.For is deprecated: use ForCompiler, which populates a FileSet with the positions of objects created by the importer."
 
-  # structcheck false-positive
   [[issues.exclude-rules]]
-    path = "interp/interp.go"
-    text = "`(astDot|cfgDot|noRun)` is unused"
+    path = "interp/.+_test\\.go"
+    linters = ["goconst"]

interp/build.go

@@ -1,6 +1,7 @@
 package interp
 
 import (
+	"go/build"
 	"go/parser"
 	"path"
 	"runtime"
@@ -57,7 +58,7 @@ func buildOptionOk(tag string) bool {
 var (
 	goos      = runtime.GOOS
 	goarch    = runtime.GOARCH
-	goversion = goNumVersion()
+	goversion = goMinorVersion(build.Default)
 )
 
 // buildTagOk returns true if a build tag matches, false otherwise
@@ -85,11 +86,20 @@ func buildTagOk(s string) (r bool) {
 	return
 }
 
-// goNumVersion returns the go minor version number
-func goNumVersion() int {
-	v := strings.Split(runtime.Version(), ".")
-	n, _ := strconv.Atoi(v[1])
-	return n
+// goMinorVersion returns the go minor version number
+func goMinorVersion(ctx build.Context) int {
+	current := ctx.ReleaseTags[len(ctx.ReleaseTags)-1]
+
+	v := strings.Split(current, ".")
+	if len(v) < 2 {
+		panic("unsupported Go version: " + current)
+	}
+
+	m, err := strconv.Atoi(v[1])
+	if err != nil {
+		panic("unsupported Go version: " + current)
+	}
+	return m
 }
 
 // skipFile returns true if file should be skipped

interp/build_test.go

@@ -1,6 +1,8 @@
 package interp
 
 import (
+	"go/build"
+	"math"
 	"testing"
 )
 
@@ -18,10 +20,45 @@ func TestBuildTag(t *testing.T) {
 	tests := []testBuild{
 		{"// +build linux", true},
 		{"// +build windows", false},
+		{"// +build go1.9", true},
 		{"// +build go1.11", true},
-		{"// +build !go1.12", true},
 		{"// +build go1.12", false},
 		{"// +build !go1.10", false},
+		{"// +build !go1.12", true},
+		{"// +build ignore", false},
+		{"// +build linux,amd64", true},
+		{"// +build linux,i386", false},
+		{"// +build linux,i386 go1.11", true},
+		{"// +build linux\n// +build amd64", true},
+		{"// +build linux\n\n\n// +build amd64", true},
+		{"// +build linux\n// +build i386", false},
+	}
+
+	i := New(Options{})
+	for _, test := range tests {
+		test := test
+		src := test.src + "\npackage x"
+		t.Run(test.src, func(t *testing.T) {
+			if r := i.buildOk("", src); r != test.res {
+				t.Errorf("got %v, want %v", r, test.res)
+			}
+		})
+	}
+}
+
+func TestBuildTagDevel(t *testing.T) {
+	// Assume a specific OS, arch and go version no matter the real underlying system
+	oo, oa, ov := goos, goarch, goversion
+	goos, goarch, goversion = "linux", "amd64", math.MaxInt16
+	defer func() { goos, goarch, goversion = oo, oa, ov }()
+
+	tests := []testBuild{
+		{"// +build linux", true},
+		{"// +build windows", false},
+		{"// +build go1.11", true},
+		{"// +build !go1.12", false},
+		{"// +build go1.12", true},
+		{"// +build !go1.10", false},
 		{"// +build go1.9", true},
 		{"// +build ignore", false},
 		{"// +build linux,amd64", true},
@@ -36,7 +73,7 @@ func TestBuildTag(t *testing.T) {
 	for _, test := range tests {
 		test := test
 		src := test.src + "\npackage x"
-		t.Run("", func(t *testing.T) {
+		t.Run(test.src, func(t *testing.T) {
 			if r := i.buildOk("", src); r != test.res {
 				t.Errorf("got %v, want %v", r, test.res)
 			}
@@ -72,3 +109,37 @@ func TestBuildFile(t *testing.T) {
 		})
 	}
 }
+
+func Test_goMinorVersion(t *testing.T) {
+	tests := []struct {
+		desc     string
+		context  build.Context
+		expected int
+	}{
+		{
+			desc: "stable",
+			context: build.Context{ReleaseTags: []string{
+				"go1.1", "go1.2", "go1.3", "go1.4", "go1.5", "go1.6", "go1.7", "go1.8", "go1.9", "go1.10", "go1.11", "go1.12",
+			}},
+			expected: 12,
+		},
+		{
+			desc: "devel/beta/rc",
+			context: build.Context{ReleaseTags: []string{
+				"go1.1", "go1.2", "go1.3", "go1.4", "go1.5", "go1.6", "go1.7", "go1.8", "go1.9", "go1.10", "go1.11", "go1.12", "go1.13",
+			}},
+			expected: 13,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			minor := goMinorVersion(test.context)
+
+			if minor != test.expected {
+				t.Errorf("got %v, want %v", minor, test.expected)
+			}
+		})
+	}
+}

stdlib/stdlib.go

@@ -1,3 +1,5 @@
+// +build go1.11,!go1.13
+
 package stdlib
 
 import "reflect"

stdlib/syscall/syscall.go

@@ -1,3 +1,5 @@
+// +build go1.11,!go1.13
+
 package syscall
 
 import "reflect"

stdlib/unsafe/unsafe.go

@@ -1,3 +1,5 @@
+// +build go1.11,!go1.13
+
 package unsafe
 
 import "reflect"