Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa4005/sa4005.go

@@ -0,0 +1,138 @@
+package sa4005
+
+import (
+	"fmt"
+	"go/types"
+
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/go/ir"
+	"honnef.co/go/tools/go/ir/irutil"
+	"honnef.co/go/tools/internal/passes/buildir"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA4005",
+		Run:      run,
+		Requires: []*analysis.Analyzer{buildir.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title:    `Field assignment that will never be observed. Did you mean to use a pointer receiver?`,
+		Since:    "2021.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	// The analysis only considers the receiver and its first level
+	// fields. It doesn't look at other parameters, nor at nested
+	// fields.
+	//
+	// The analysis does not detect all kinds of dead stores, only
+	// those of fields that are never read after the write. That is,
+	// we do not flag 'a.x = 1; a.x = 2; _ = a.x'. We might explore
+	// this again if we add support for SROA to go/ir and implement
+	// https://github.com/dominikh/go-tools/issues/191.
+
+	irpkg := pass.ResultOf[buildir.Analyzer].(*buildir.IR)
+fnLoop:
+	for _, fn := range irpkg.SrcFuncs {
+		if recv := fn.Signature.Recv(); recv == nil {
+			continue
+		} else if _, ok := recv.Type().Underlying().(*types.Struct); !ok {
+			continue
+		}
+
+		recv := fn.Params[0]
+		refs := irutil.FilterDebug(*recv.Referrers())
+		if len(refs) != 1 {
+			continue
+		}
+		store, ok := refs[0].(*ir.Store)
+		if !ok {
+			continue
+		}
+		alloc, ok := store.Addr.(*ir.Alloc)
+		if !ok || alloc.Heap {
+			continue
+		}
+
+		reads := map[int][]ir.Instruction{}
+		writes := map[int][]ir.Instruction{}
+		for _, ref := range *alloc.Referrers() {
+			switch ref := ref.(type) {
+			case *ir.FieldAddr:
+				for _, refref := range *ref.Referrers() {
+					switch refref.(type) {
+					case *ir.Store:
+						writes[ref.Field] = append(writes[ref.Field], refref)
+					case *ir.Load:
+						reads[ref.Field] = append(reads[ref.Field], refref)
+					case *ir.DebugRef:
+						continue
+					default:
+						// this should be safe… if the field address
+						// escapes, then alloc.Heap will be true.
+						// there should be no instructions left that,
+						// given this FieldAddr, without escaping, can
+						// effect a load or store.
+						continue
+					}
+				}
+			case *ir.Store:
+				// we could treat this as a store to every field, but
+				// we don't want to decide the semantics of partial
+				// struct initializers. should `v = t{x: 1}` also mark
+				// v.y as being written to?
+				if ref != store {
+					continue fnLoop
+				}
+			case *ir.Load:
+				// a load of the entire struct loads every field
+				for i := 0; i < recv.Type().Underlying().(*types.Struct).NumFields(); i++ {
+					reads[i] = append(reads[i], ref)
+				}
+			case *ir.DebugRef:
+				continue
+			default:
+				continue fnLoop
+			}
+		}
+
+		offset := func(instr ir.Instruction) int {
+			for i, other := range instr.Block().Instrs {
+				if instr == other {
+					return i
+				}
+			}
+			panic("couldn't find instruction in its block")
+		}
+
+		for field, ws := range writes {
+			rs := reads[field]
+		wLoop:
+			for _, w := range ws {
+				for _, r := range rs {
+					if w.Block() == r.Block() {
+						if offset(r) > offset(w) {
+							// found a reachable read of our write
+							continue wLoop
+						}
+					} else if irutil.Reachable(w.Block(), r.Block()) {
+						// found a reachable read of our write
+						continue wLoop
+					}
+				}
+				fieldName := recv.Type().Underlying().(*types.Struct).Field(field).Name()
+				report.Report(pass, w, fmt.Sprintf("ineffective assignment to field %s.%s", recv.Type().(interface{ Obj() *types.TypeName }).Obj().Name(), fieldName))
+			}
+		}
+	}
+	return nil, nil
+}