SA1032: add check for errors.Is() and .As() argument order

Fixes #1530

knowledge/arg.go

@@ -22,6 +22,8 @@ var Args = map[string]int{
 	"(*encoding/json.Encoder).Encode.v":      0,
 	"(*encoding/xml.Decoder).Decode.v":       0,
 	"(*encoding/xml.Encoder).Encode.v":       0,
+	"errors.As.err":                          0,
+	"errors.Is.err":                          0,
 	"errors.New.text":                        0,
 	"fmt.Fprintf.format":                     1,
 	"fmt.Printf.format":                      0,

staticcheck/sa1032/sa1032.go

@@ -0,0 +1,55 @@
+package sa1032
+
+import (
+	"honnef.co/go/tools/analysis/callcheck"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/go/ir"
+	"honnef.co/go/tools/internal/passes/buildir"
+	"honnef.co/go/tools/knowledge"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA1032",
+		Requires: []*analysis.Analyzer{buildir.Analyzer},
+		Run:      callcheck.Analyzer(rules),
+	},
+	Doc: &lint.Documentation{
+		Title: `Swapped arguments in errors.Is() or errors.As()`,
+		Text: `
+If the first argument to \'errors.As()\' or \'errors.Is()\' contains a package
+selector it assumes the error and target were swapped, since the target should
+practically always be a local variable and not a reference to another package.
+`,
+		Since:    "Unreleased",
+		Severity: lint.SeverityError,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+var rules = map[string]callcheck.Check{
+	"errors.As": func(call *callcheck.Call) {
+		validateIs(call.Pass.Pkg.Path(), call.Args[knowledge.Arg("errors.As.err")])
+	},
+	"errors.Is": func(call *callcheck.Call) {
+		validateIs(call.Pass.Pkg.Path(), call.Args[knowledge.Arg("errors.Is.err")])
+	},
+}
+
+func validateIs(curPkg string, arg *callcheck.Argument) {
+	v, ok := arg.Value.Value.(*ir.Load)
+	if !ok {
+		return
+	}
+	g, ok := v.X.(*ir.Global)
+	if !ok {
+		return
+	}
+	if pkg := g.Package().Pkg; pkg != nil && pkg.Path() != curPkg {
+		arg.Invalid("arguments have the wrong order")
+	}
+}

staticcheck/sa1032/testdata/go1.0/example.com/ErrorsOrder/ErrorsOrder.go

@@ -0,0 +1,76 @@
+package errors
+
+import (
+	"errors"
+	"io/fs"
+)
+
+var gErr = errors.New("global")
+
+type myErr struct{}
+
+func (myErr) Error() string { return "" }
+
+func is() {
+	err := errors.New("oh noes")
+
+	_ = errors.Is(err, fs.ErrNotExist)
+	_ = errors.Is(fs.ErrNotExist, err) //@ diag(`wrong order`)
+	if errors.Is(err, fs.ErrNotExist) {
+	}
+	if errors.Is(fs.ErrNotExist, err) { //@ diag(`wrong order`)
+	}
+
+	_ = errors.Is(gErr, fs.ErrNotExist)
+	_ = errors.Is(fs.ErrNotExist, gErr) //@ diag(`wrong order`)
+	if errors.Is(gErr, fs.ErrNotExist) {
+	}
+	if errors.Is(fs.ErrNotExist, gErr) { //@ diag(`wrong order`)
+	}
+
+	_ = errors.Is(myErr{}, fs.ErrNotExist)
+	_ = errors.Is(fs.ErrNotExist, myErr{}) //@ diag(`wrong order`)
+	if errors.Is(myErr{}, fs.ErrNotExist) {
+	}
+	if errors.Is(fs.ErrNotExist, myErr{}) { //@ diag(`wrong order`)
+	}
+
+	_ = errors.Is(&myErr{}, fs.ErrNotExist)
+	_ = errors.Is(fs.ErrNotExist, &myErr{}) //@ diag(`wrong order`)
+	if errors.Is(&myErr{}, fs.ErrNotExist) {
+	}
+	if errors.Is(fs.ErrNotExist, &myErr{}) { //@ diag(`wrong order`)
+	}
+}
+
+func as() {
+	err := errors.New("oh noes")
+
+	_ = errors.As(err, fs.ErrNotExist)
+	_ = errors.As(fs.ErrNotExist, err) //@ diag(`wrong order`)
+	if errors.As(err, fs.ErrNotExist) {
+	}
+	if errors.As(fs.ErrNotExist, err) { //@ diag(`wrong order`)
+	}
+
+	_ = errors.As(gErr, fs.ErrNotExist)
+	_ = errors.As(fs.ErrNotExist, gErr) //@ diag(`wrong order`)
+	if errors.As(gErr, fs.ErrNotExist) {
+	}
+	if errors.As(fs.ErrNotExist, gErr) { //@ diag(`wrong order`)
+	}
+
+	_ = errors.As(myErr{}, fs.ErrNotExist)
+	_ = errors.As(fs.ErrNotExist, myErr{}) //@ diag(`wrong order`)
+	if errors.As(myErr{}, fs.ErrNotExist) {
+	}
+	if errors.As(fs.ErrNotExist, myErr{}) { //@ diag(`wrong order`)
+	}
+
+	_ = errors.As(&myErr{}, fs.ErrNotExist)
+	_ = errors.As(fs.ErrNotExist, &myErr{}) //@ diag(`wrong order`)
+	if errors.As(&myErr{}, fs.ErrNotExist) {
+	}
+	if errors.As(fs.ErrNotExist, &myErr{}) { //@ diag(`wrong order`)
+	}
+}