go/analysis/passes/buildtag: report invalid go versions in build tags.

Report invalid Go versions within build tags. Additionally reports
likely misspellings of Go version tags.

Fixes golang/go#64127

Change-Id: I9b698c94c7da29aafbe45b4c90d58c0bfe8efa1d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/597576
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: timothy-king

go/analysis/passes/buildtag/buildtag.go

@@ -15,6 +15,7 @@ import (
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
+	"golang.org/x/tools/internal/versions"
 )
 
 const Doc = "check //go:build and // +build directives"
@@ -264,6 +265,8 @@ func (check *checker) goBuildLine(pos token.Pos, line string) {
 		return
 	}
 
+	check.tags(pos, x)
+
 	if check.goBuild == nil {
 		check.goBuild = x
 	}
@@ -323,6 +326,8 @@ func (check *checker) plusBuildLine(pos token.Pos, line string) {
 			check.crossCheck = false
 			return
 		}
+		check.tags(pos, y)
+
 		if check.plusBuild == nil {
 			check.plusBuild = y
 		} else {
@@ -363,3 +368,51 @@ func (check *checker) finish() {
 		return
 	}
 }
+
+// tags reports issues in go versions in tags within the expression e.
+func (check *checker) tags(pos token.Pos, e constraint.Expr) {
+	// Check that constraint.GoVersion is meaningful (>= go1.21).
+	if versions.ConstraintGoVersion == nil {
+		return
+	}
+
+	// Use Eval to visit each tag.
+	_ = e.Eval(func(tag string) bool {
+		if malformedGoTag(tag) {
+			check.pass.Reportf(pos, "invalid go version %q in build constraint", tag)
+		}
+		return false // result is immaterial as Eval does not short-circuit
+	})
+}
+
+// malformedGoTag returns true if a tag is likely to be a malformed
+// go version constraint.
+func malformedGoTag(tag string) bool {
+	// Not a go version?
+	if !strings.HasPrefix(tag, "go1") {
+		// Check for close misspellings of the "go1." prefix.
+		for _, pre := range []string{"go.", "g1.", "go"} {
+			suffix := strings.TrimPrefix(tag, pre)
+			if suffix != tag {
+				if valid, ok := validTag("go1." + suffix); ok && valid {
+					return true
+				}
+			}
+		}
+		return false
+	}
+
+	// The tag starts with "go1" so it is almost certainly a GoVersion.
+	// Report it if it is not a valid build constraint.
+	valid, ok := validTag(tag)
+	return ok && !valid
+}
+
+// validTag returns (valid, ok) where valid reports when a tag is valid,
+// and ok reports determining if the tag is valid succeeded.
+func validTag(tag string) (valid bool, ok bool) {
+	if versions.ConstraintGoVersion != nil {
+		return versions.ConstraintGoVersion(&constraint.TagExpr{Tag: tag}) != "", true
+	}
+	return false, false
+}

go/analysis/passes/buildtag/buildtag_test.go

@@ -10,6 +10,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/analysistest"
 	"golang.org/x/tools/go/analysis/passes/buildtag"
+	"golang.org/x/tools/internal/versions"
 )
 
 func Test(t *testing.T) {
@@ -30,5 +31,9 @@ func Test(t *testing.T) {
 
 		return buildtag.Analyzer.Run(pass)
 	}
-	analysistest.Run(t, analysistest.TestData(), &analyzer, "a")
+	patterns := []string{"a"}
+	if versions.ConstraintGoVersion != nil {
+		patterns = append(patterns, "b")
+	}
+	analysistest.Run(t, analysistest.TestData(), &analyzer, patterns...)
 }

go/analysis/passes/buildtag/testdata/src/b/vers.go

@@ -0,0 +1,10 @@
+// Copyright 2024 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.
+
+// want +3 `invalid go version \"go1.20.1\" in build constraint`
+// want +1 `invalid go version \"go1.20.1\" in build constraint`
+//go:build go1.20.1
+// +build go1.20.1
+
+package b

go/analysis/passes/buildtag/testdata/src/b/vers1.go

@@ -0,0 +1,7 @@
+// Copyright 2024 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.
+
+// This file is intentionally so its build tags always match.
+
+package b

go/analysis/passes/buildtag/testdata/src/b/vers2.go

@@ -0,0 +1,8 @@
+// Copyright 2024 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.
+
+// want +1 `invalid go version \"go120\" in build constraint`
+//go:build go120
+
+package b

go/analysis/passes/buildtag/testdata/src/b/vers3.go

@@ -0,0 +1,8 @@
+// Copyright 2024 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.
+
+// want +1 `invalid go version \"go1..20\" in build constraint`
+//go:build go1..20
+
+package b

go/analysis/passes/buildtag/testdata/src/b/vers4.go

@@ -0,0 +1,8 @@
+// Copyright 2024 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.
+
+// want +1 `invalid go version \"go.20\" in build constraint`
+//go:build go.20
+
+package b

go/analysis/passes/buildtag/testdata/src/b/vers5.go

@@ -0,0 +1,8 @@
+// Copyright 2024 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.
+
+// want +1 `invalid go version \"g1.20\" in build constraint`
+//go:build g1.20
+
+package b

go/analysis/passes/buildtag/testdata/src/b/vers6.go

@@ -0,0 +1,8 @@
+// Copyright 2024 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.
+
+// want +1 `invalid go version \"go20\" in build constraint`
+//go:build go20
+
+package b

internal/versions/constraint.go

@@ -0,0 +1,13 @@
+// Copyright 2024 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 versions
+
+import "go/build/constraint"
+
+// ConstraintGoVersion is constraint.GoVersion (if built with go1.21+).
+// Otherwise nil.
+//
+// Deprecate once x/tools is after go1.21.
+var ConstraintGoVersion func(x constraint.Expr) string

internal/versions/constraint_go121.go

@@ -0,0 +1,14 @@
+// Copyright 2024 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.
+
+//go:build go1.21
+// +build go1.21
+
+package versions
+
+import "go/build/constraint"
+
+func init() {
+	ConstraintGoVersion = constraint.GoVersion
+}