Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa9008/sa9008.go

@@ -0,0 +1,124 @@
+package sa9008
+
+import (
+	"fmt"
+	"go/ast"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/go/ast/astutil"
+	"honnef.co/go/tools/go/ir"
+	"honnef.co/go/tools/go/ir/irutil"
+	"honnef.co/go/tools/internal/passes/buildir"
+	"honnef.co/go/tools/pattern"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA9008",
+		Run:      run,
+		Requires: append([]*analysis.Analyzer{buildir.Analyzer}, code.RequiredAnalyzers...),
+	},
+	Doc: &lint.RawDocumentation{
+		Title: `\'else\' branch of a type assertion is probably not reading the right value`,
+		Text: `
+When declaring variables as part of an \'if\' statement (like in \"if
+foo := ...; foo {\"), the same variables will also be in the scope of
+the \'else\' branch. This means that in the following example
+
+    if x, ok := x.(int); ok {
+        // ...
+    } else {
+        fmt.Printf("unexpected type %T", x)
+    }
+
+\'x\' in the \'else\' branch will refer to the \'x\' from \'x, ok
+:=\'; it will not refer to the \'x\' that is being type-asserted. The
+result of a failed type assertion is the zero value of the type that
+is being asserted to, so \'x\' in the else branch will always have the
+value \'0\' and the type \'int\'.
+`,
+		Since:    "2022.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+var typeAssertionShadowingElseQ = pattern.MustParse(`(IfStmt (AssignStmt [obj@(Ident _) ok@(Ident _)] ":=" assert@(TypeAssertExpr obj _)) ok _ elseBranch)`)
+
+func run(pass *analysis.Pass) (any, error) {
+	// TODO(dh): without the IR-based verification, this check is able
+	// to find more bugs, but also more prone to false positives. It
+	// would be a good candidate for the 'codereview' category of
+	// checks.
+
+	irpkg := pass.ResultOf[buildir.Analyzer].(*buildir.IR).Pkg
+	for _, m := range code.Matches(pass, typeAssertionShadowingElseQ) {
+		shadow := pass.TypesInfo.ObjectOf(m.State["obj"].(*ast.Ident))
+		shadowed := m.State["assert"].(*ast.TypeAssertExpr).X
+
+		path, exact := astutil.PathEnclosingInterval(code.File(pass, shadow), shadow.Pos(), shadow.Pos())
+		if !exact {
+			// TODO(dh): when can this happen?
+			continue
+		}
+		irfn := ir.EnclosingFunction(irpkg, path)
+		if irfn == nil {
+			// For example for functions named "_", because we don't generate IR for them.
+			continue
+		}
+
+		shadoweeIR, isAddr := irfn.ValueForExpr(m.State["obj"].(*ast.Ident))
+		if shadoweeIR == nil || isAddr {
+			// TODO(dh): is this possible?
+			continue
+		}
+
+		var branch ast.Node
+		switch br := m.State["elseBranch"].(type) {
+		case ast.Node:
+			branch = br
+		case []ast.Stmt:
+			branch = &ast.BlockStmt{List: br}
+		case nil:
+			continue
+		default:
+			panic(fmt.Sprintf("unexpected type %T", br))
+		}
+
+		ast.Inspect(branch, func(node ast.Node) bool {
+			ident, ok := node.(*ast.Ident)
+			if !ok {
+				return true
+			}
+			if pass.TypesInfo.ObjectOf(ident) != shadow {
+				return true
+			}
+
+			v, isAddr := irfn.ValueForExpr(ident)
+			if v == nil || isAddr {
+				return true
+			}
+			if irutil.Flatten(v) != shadoweeIR {
+				// Same types.Object, but different IR value. This
+				// either means that the variable has been
+				// assigned to since the type assertion, or that
+				// the variable has escaped to the heap. Either
+				// way, we shouldn't flag reads of it.
+				return true
+			}
+
+			report.Report(pass, ident,
+				fmt.Sprintf("%s refers to the result of a failed type assertion and is a zero value, not the value that was being type-asserted", report.Render(pass, ident)),
+				report.Related(shadow, "this is the variable being read"),
+				report.Related(shadowed, "this is the variable being shadowed"))
+			return true
+		})
+	}
+	return nil, nil
+}