staticcheck: handle imports of deprecated github.com/golang/protobuf/…

…proto specially

github.com/golang/protobuf has deprecated the proto package, but their
protoc-gen-go still imports the package and uses one of its constants,
"to enforce a weak dependency on a sufficiently new version of the
legacy package".

Staticcheck would flag the import of this deprecated package in all
code generated by protoc-gen-go. Instead of forcing the project to
change their project structure, we choose to ignore such imports in
code generated by protoc-gen-go. The import still gets flagged in code
not generated by protoc-gen-go.

Upstream issue: golang/protobuf#1077

facts/generated.go

@@ -19,6 +19,7 @@ const (
 	Goyacc
 	Cgo
 	Stringer
+	ProtocGenGo
 )
 
 var (
@@ -51,6 +52,8 @@ func isGenerated(path string) (Generator, bool) {
 				return Goyacc, true
 			case "by cmd/cgo;":
 				return Cgo, true
+			case "by protoc-gen-go.":
+				return ProtocGenGo, true
 			}
 			if strings.HasPrefix(text, `by "stringer `) {
 				return Stringer, true

staticcheck/analysis.go

@@ -66,7 +66,7 @@ var Analyzers = lintutil.InitializeAnalyzers(Docs, map[string]*analysis.Analyzer
 	"SA1018": makeCallCheckerAnalyzer(checkStringsReplaceZeroRules),
 	"SA1019": {
 		Run:      CheckDeprecated,
-		Requires: []*analysis.Analyzer{inspect.Analyzer, facts.Deprecated},
+		Requires: []*analysis.Analyzer{inspect.Analyzer, facts.Deprecated, facts.Generated},
 	},
 	"SA1020": makeCallCheckerAnalyzer(checkListenAddressRules),
 	"SA1021": makeCallCheckerAnalyzer(checkBytesEqualIPRules),

staticcheck/lint.go

@@ -2927,6 +2927,12 @@ func CheckDeprecated(pass *analysis.Pass) (interface{}, error) {
 		p := spec.Path.Value
 		path := p[1 : len(p)-1]
 		if depr, ok := deprs.Packages[imp]; ok {
+			if path == "github.com/golang/protobuf/proto" {
+				gen, ok := code.Generator(pass, spec.Path.Pos())
+				if ok && gen == facts.ProtocGenGo {
+					return
+				}
+			}
 			report.Report(pass, spec, fmt.Sprintf("package %s is deprecated: %s", path, depr.Msg))
 		}
 	}

staticcheck/testdata/src/CheckDeprecated/not-protobuf.go

@@ -0,0 +1,3 @@
+package pkg
+
+import _ "github.com/golang/protobuf/proto" // want `Alas, it is deprecated\.`

staticcheck/testdata/src/github.com/golang/protobuf/proto/pkg.go

@@ -0,0 +1,4 @@
+// Package proto exists.
+//
+// Deprecated: Alas, it is deprecated.
+package proto