gopls/internal/analysis/unusedparams/unusedparams.go - tools - Git at Google

 // Copyright 2020 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 unusedparams

 import (
 	_ "embed"
 	"fmt"
 	"go/ast"
 	"go/types"

 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
 	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/internal/analysisinternal"
 )

 //go:embed doc.go
 var doc string

 var Analyzer = &analysis.Analyzer{
 	Name:     "unusedparams",
 	Doc:      analysisinternal.MustExtractDoc(doc, "unusedparams"),
 	Requires: []*analysis.Analyzer{inspect.Analyzer},
 	Run:      run,
 	URL:      "https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/unusedparams",
 }

 const FixCategory = "unusedparams" // recognized by gopls ApplyFix

 func run(pass *analysis.Pass) (any, error) {
 	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)

 	// First find all "address-taken" functions.
 	// We must conservatively assume that their parameters
 	// are all required to conform to some signature.
 	//
 	// A named function is address-taken if it is somewhere
 	// used not in call position:
 	//
 	//	f(...)		// not address-taken
 	//      use(f)          // address-taken
 	//
 	// A literal function is address-taken if it is not
 	// immediately bound to a variable, or if that variable is
 	// used not in call position:
 	//
 	//    f := func() { ... }; f()     			used only in call position
 	//    var f func(); f = func() { ...f()... }; f()     	ditto
 	//    use(func() { ... })				address-taken
 	//

 	// Note: this algorithm relies on the assumption that the
 	// analyzer is called only for the "widest" package for a
 	// given file: that is, p_test in preference to p, if both
 	// exist. Analyzing only package p may produce diagnostics
 	// that would be falsified based on declarations in p_test.go
 	// files. The gopls analysis driver does this, but most
 	// drivers to not, so running this command in, say,
 	// unitchecker or multichecker may produce incorrect results.

 	// Gather global information:
 	// - uses of functions not in call position
 	// - unexported interface methods
 	// - all referenced variables

 	usesOutsideCall := make(map[types.Object][]*ast.Ident)
 	unexportedIMethodNames := make(map[string]bool)
 	{
 		callPosn := make(map[*ast.Ident]bool) // all idents f appearing in f() calls
 		filter := []ast.Node{
 			(*ast.CallExpr)(nil),
 			(*ast.InterfaceType)(nil),
 		}
 		inspect.Preorder(filter, func(n ast.Node) {
 			switch n := n.(type) {
 			case *ast.CallExpr:
 				// Strip off any generic instantiation.
 				fun := n.Fun
 				switch fun_ := fun.(type) {
 				case *ast.IndexExpr:
 					fun = fun_.X // f[T]()  (funcs[i]() is rejected below)
 				case *ast.IndexListExpr:
 					fun = fun_.X // f[K, V]()
 				}

 				// Find object:
 				// record non-exported function, method, or func-typed var.
 				var id *ast.Ident
 				switch fun := fun.(type) {
 				case *ast.Ident:
 					id = fun
 				case *ast.SelectorExpr:
 					id = fun.Sel
 				}
 				if id != nil && !id.IsExported() {
 					switch pass.TypesInfo.Uses[id].(type) {
 					case *types.Func, *types.Var:
 						callPosn[id] = true
 					}
 				}

 			case *ast.InterfaceType:
 				// Record the set of names of unexported interface methods.
 				// (It would be more precise to record signatures but
 				// generics makes it tricky, and this conservative
 				// heuristic is close enough.)
 				t := pass.TypesInfo.TypeOf(n).(*types.Interface)
 				for i := 0; i < t.NumExplicitMethods(); i++ {
 					m := t.ExplicitMethod(i)
 					if !m.Exported() && m.Name() != "_" {
 						unexportedIMethodNames[m.Name()] = true
 					}
 				}
 			}
 		})

 		for id, obj := range pass.TypesInfo.Uses {
 			if !callPosn[id] {
 				// This includes "f = func() {...}", which we deal with below.
 				usesOutsideCall[obj] = append(usesOutsideCall[obj], id)
 			}
 		}
 	}

 	// Find all vars (notably parameters) that are used.
 	usedVars := make(map[*types.Var]bool)
 	for _, obj := range pass.TypesInfo.Uses {
 		if v, ok := obj.(*types.Var); ok {
 			if v.IsField() {
 				continue // no point gathering these
 			}
 			usedVars[v] = true
 		}
 	}

 	// Check each non-address-taken function's parameters are all used.
 	filter := []ast.Node{
 		(*ast.FuncDecl)(nil),
 		(*ast.FuncLit)(nil),
 	}
 	inspect.WithStack(filter, func(n ast.Node, push bool, stack []ast.Node) bool {
 		// (We always return true so that we visit nested FuncLits.)

 		if !push {
 			return true
 		}

 		var (
 			fn    types.Object // function symbol (*Func, possibly *Var for a FuncLit)
 			ftype *ast.FuncType
 			body  *ast.BlockStmt
 		)
 		switch n := n.(type) {
 		case *ast.FuncDecl:
 			// We can't analyze non-Go functions.
 			if n.Body == nil {
 				return true
 			}

 			// Ignore exported functions and methods: we
 			// must assume they may be address-taken in
 			// another package.
 			if n.Name.IsExported() {
 				return true
 			}

 			// Ignore methods that match the name of any
 			// interface method declared in this package,
 			// as the method's signature may need to conform
 			// to the interface.
 			if n.Recv != nil && unexportedIMethodNames[n.Name.Name] {
 				return true
 			}

 			fn = pass.TypesInfo.Defs[n.Name].(*types.Func)
 			ftype, body = n.Type, n.Body

 		case *ast.FuncLit:
 			// Find the symbol for the variable (if any)
 			// to which the FuncLit is bound.
 			// (We don't bother to allow ParenExprs.)
 			switch parent := stack[len(stack)-2].(type) {
 			case *ast.AssignStmt:
 				// f  = func() {...}
 				// f := func() {...}
 				for i, rhs := range parent.Rhs {
 					if rhs == n {
 						if id, ok := parent.Lhs[i].(*ast.Ident); ok {
 							fn = pass.TypesInfo.ObjectOf(id)

 							// Edge case: f = func() {...}
 							// should not count as a use.
 							if pass.TypesInfo.Uses[id] != nil {
 								usesOutsideCall[fn] = moreslices.Remove(usesOutsideCall[fn], id)
 							}

 							if fn == nil && id.Name == "_" {
 								// Edge case: _ = func() {...}
 								// has no var. Fake one.
 								fn = types.NewVar(id.Pos(), pass.Pkg, id.Name, pass.TypesInfo.TypeOf(n))
 							}
 						}
 						break
 					}
 				}

 			case *ast.ValueSpec:
 				// var f = func() { ... }
 				// (unless f is an exported package-level var)
 				for i, val := range parent.Values {
 					if val == n {
 						v := pass.TypesInfo.Defs[parent.Names[i]]
 						if !(v.Parent() == pass.Pkg.Scope() && v.Exported()) {
 							fn = v
 						}
 						break
 					}
 				}
 			}

 			ftype, body = n.Type, n.Body
 		}

 		// Ignore address-taken functions and methods: unused
 		// parameters may be needed to conform to a func type.
 		if fn == nil || len(usesOutsideCall[fn]) > 0 {
 			return true
 		}

 		// If there are no parameters, there are no unused parameters.
 		if ftype.Params.NumFields() == 0 {
 			return true
 		}

 		// To reduce false positives, ignore functions with an
 		// empty or panic body.
 		//
 		// We choose not to ignore functions whose body is a
 		// single return statement (as earlier versions did)
 		// 	func f() { return }
 		// 	func f() { return g(...) }
 		// as we suspect that was just heuristic to reduce
 		// false positives in the earlier unsound algorithm.
 		switch len(body.List) {
 		case 0:
 			// Empty body. Although the parameter is
 			// unnecessary, it's pretty obvious to the
 			// reader that that's the case, so we allow it.
 			return true // func f() {}
 		case 1:
 			if stmt, ok := body.List[0].(*ast.ExprStmt); ok {
 				// We allow a panic body, as it is often a
 				// placeholder for a future implementation:
 				// 	func f() { panic(...) }
 				if call, ok := stmt.X.(*ast.CallExpr); ok {
 					if fun, ok := call.Fun.(*ast.Ident); ok && fun.Name == "panic" {
 						return true
 					}
 				}
 			}
 		}

 		// Report each unused parameter.
 		for _, field := range ftype.Params.List {
 			for _, id := range field.Names {
 				if id.Name == "_" {
 					continue
 				}
 				param := pass.TypesInfo.Defs[id].(*types.Var)
 				if !usedVars[param] {
 					start, end := field.Pos(), field.End()
 					if len(field.Names) > 1 {
 						start, end = id.Pos(), id.End()
 					}
 					// This diagnostic carries both an edit-based fix to
 					// rename the unused parameter, and a command-based fix
 					// to remove it (see golang.RemoveUnusedParameter).
 					pass.Report(analysis.Diagnostic{
 						Pos:      start,
 						End:      end,
 						Message:  fmt.Sprintf("unused parameter: %s", id.Name),
 						Category: FixCategory,
 						SuggestedFixes: []analysis.SuggestedFix{
 							{
 								Message: `Rename parameter to "_"`,
 								TextEdits: []analysis.TextEdit{{
 									Pos:     id.Pos(),
 									End:     id.End(),
 									NewText: []byte("_"),
 								}},
 							},
 							{
 								Message: fmt.Sprintf("Remove unused parameter %q", id.Name),
 								// No TextEdits => computed by gopls command
 							},
 						},
 					})
 				}
 			}
 		}

 		return true
 	})
 	return nil, nil
 }
	// Copyright 2020 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 unusedparams

	import (
	_ "embed"
	"fmt"
	"go/ast"
	"go/types"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/analysis/passes/inspect"
	"golang.org/x/tools/go/ast/inspector"
	"golang.org/x/tools/gopls/internal/util/moreslices"
	"golang.org/x/tools/internal/analysisinternal"
	)

	//go:embed doc.go
	var doc string

	var Analyzer = &analysis.Analyzer{
	Name: "unusedparams",
	Doc: analysisinternal.MustExtractDoc(doc, "unusedparams"),
	Requires: []*analysis.Analyzer{inspect.Analyzer},
	Run: run,
	URL: "https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/unusedparams",
	}

	const FixCategory = "unusedparams" // recognized by gopls ApplyFix

	func run(pass *analysis.Pass) (any, error) {
	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)

	// First find all "address-taken" functions.
	// We must conservatively assume that their parameters
	// are all required to conform to some signature.
	//
	// A named function is address-taken if it is somewhere
	// used not in call position:
	//
	// f(...) // not address-taken
	// use(f) // address-taken
	//
	// A literal function is address-taken if it is not
	// immediately bound to a variable, or if that variable is
	// used not in call position:
	//
	// f := func() { ... }; f() used only in call position
	// var f func(); f = func() { ...f()... }; f() ditto
	// use(func() { ... }) address-taken
	//

	// Note: this algorithm relies on the assumption that the
	// analyzer is called only for the "widest" package for a
	// given file: that is, p_test in preference to p, if both
	// exist. Analyzing only package p may produce diagnostics
	// that would be falsified based on declarations in p_test.go
	// files. The gopls analysis driver does this, but most
	// drivers to not, so running this command in, say,
	// unitchecker or multichecker may produce incorrect results.

	// Gather global information:
	// - uses of functions not in call position
	// - unexported interface methods
	// - all referenced variables

	usesOutsideCall := make(map[types.Object][]*ast.Ident)
	unexportedIMethodNames := make(map[string]bool)
	{
	callPosn := make(map[*ast.Ident]bool) // all idents f appearing in f() calls
	filter := []ast.Node{
	(*ast.CallExpr)(nil),
	(*ast.InterfaceType)(nil),
	}
	inspect.Preorder(filter, func(n ast.Node) {
	switch n := n.(type) {
	case *ast.CallExpr:
	// Strip off any generic instantiation.
	fun := n.Fun
	switch fun_ := fun.(type) {
	case *ast.IndexExpr:
	fun = fun_.X // f[T]() (funcs[i]() is rejected below)
	case *ast.IndexListExpr:
	fun = fun_.X // f[K, V]()
	}

	// Find object:
	// record non-exported function, method, or func-typed var.
	var id *ast.Ident
	switch fun := fun.(type) {
	case *ast.Ident:
	id = fun
	case *ast.SelectorExpr:
	id = fun.Sel
	}
	if id != nil && !id.IsExported() {
	switch pass.TypesInfo.Uses[id].(type) {
	case types.Func, types.Var:
	callPosn[id] = true
	}
	}

	case *ast.InterfaceType:
	// Record the set of names of unexported interface methods.
	// (It would be more precise to record signatures but
	// generics makes it tricky, and this conservative
	// heuristic is close enough.)
	t := pass.TypesInfo.TypeOf(n).(*types.Interface)
	for i := 0; i < t.NumExplicitMethods(); i++ {
	m := t.ExplicitMethod(i)
	if !m.Exported() && m.Name() != "_" {
	unexportedIMethodNames[m.Name()] = true
	}
	}
	}
	})

	for id, obj := range pass.TypesInfo.Uses {
	if !callPosn[id] {
	// This includes "f = func() {...}", which we deal with below.
	usesOutsideCall[obj] = append(usesOutsideCall[obj], id)
	}
	}
	}

	// Find all vars (notably parameters) that are used.
	usedVars := make(map[*types.Var]bool)
	for _, obj := range pass.TypesInfo.Uses {
	if v, ok := obj.(*types.Var); ok {
	if v.IsField() {
	continue // no point gathering these
	}
	usedVars[v] = true
	}
	}

	// Check each non-address-taken function's parameters are all used.
	filter := []ast.Node{
	(*ast.FuncDecl)(nil),
	(*ast.FuncLit)(nil),
	}
	inspect.WithStack(filter, func(n ast.Node, push bool, stack []ast.Node) bool {
	// (We always return true so that we visit nested FuncLits.)

	if !push {
	return true
	}

	var (
	fn types.Object // function symbol (Func, possibly Var for a FuncLit)
	ftype *ast.FuncType
	body *ast.BlockStmt
	)
	switch n := n.(type) {
	case *ast.FuncDecl:
	// We can't analyze non-Go functions.
	if n.Body == nil {
	return true
	}

	// Ignore exported functions and methods: we
	// must assume they may be address-taken in
	// another package.
	if n.Name.IsExported() {
	return true
	}

	// Ignore methods that match the name of any
	// interface method declared in this package,
	// as the method's signature may need to conform
	// to the interface.
	if n.Recv != nil && unexportedIMethodNames[n.Name.Name] {
	return true
	}

	fn = pass.TypesInfo.Defs[n.Name].(*types.Func)
	ftype, body = n.Type, n.Body

	case *ast.FuncLit:
	// Find the symbol for the variable (if any)
	// to which the FuncLit is bound.
	// (We don't bother to allow ParenExprs.)
	switch parent := stack[len(stack)-2].(type) {
	case *ast.AssignStmt:
	// f = func() {...}
	// f := func() {...}
	for i, rhs := range parent.Rhs {
	if rhs == n {
	if id, ok := parent.Lhs[i].(*ast.Ident); ok {
	fn = pass.TypesInfo.ObjectOf(id)

	// Edge case: f = func() {...}
	// should not count as a use.
	if pass.TypesInfo.Uses[id] != nil {
	usesOutsideCall[fn] = moreslices.Remove(usesOutsideCall[fn], id)
	}

	if fn == nil && id.Name == "_" {
	// Edge case: _ = func() {...}
	// has no var. Fake one.
	fn = types.NewVar(id.Pos(), pass.Pkg, id.Name, pass.TypesInfo.TypeOf(n))
	}
	}
	break
	}
	}

	case *ast.ValueSpec:
	// var f = func() { ... }
	// (unless f is an exported package-level var)
	for i, val := range parent.Values {
	if val == n {
	v := pass.TypesInfo.Defs[parent.Names[i]]
	if !(v.Parent() == pass.Pkg.Scope() && v.Exported()) {
	fn = v
	}
	break
	}
	}
	}

	ftype, body = n.Type, n.Body
	}

	// Ignore address-taken functions and methods: unused
	// parameters may be needed to conform to a func type.
	if fn == nil \|\| len(usesOutsideCall[fn]) > 0 {
	return true
	}

	// If there are no parameters, there are no unused parameters.
	if ftype.Params.NumFields() == 0 {
	return true
	}

	// To reduce false positives, ignore functions with an
	// empty or panic body.
	//
	// We choose not to ignore functions whose body is a
	// single return statement (as earlier versions did)
	// func f() { return }
	// func f() { return g(...) }
	// as we suspect that was just heuristic to reduce
	// false positives in the earlier unsound algorithm.
	switch len(body.List) {
	case 0:
	// Empty body. Although the parameter is
	// unnecessary, it's pretty obvious to the
	// reader that that's the case, so we allow it.
	return true // func f() {}
	case 1:
	if stmt, ok := body.List[0].(*ast.ExprStmt); ok {
	// We allow a panic body, as it is often a
	// placeholder for a future implementation:
	// func f() { panic(...) }
	if call, ok := stmt.X.(*ast.CallExpr); ok {
	if fun, ok := call.Fun.(*ast.Ident); ok && fun.Name == "panic" {
	return true
	}
	}
	}
	}

	// Report each unused parameter.
	for _, field := range ftype.Params.List {
	for _, id := range field.Names {
	if id.Name == "_" {
	continue
	}
	param := pass.TypesInfo.Defs[id].(*types.Var)
	if !usedVars[param] {
	start, end := field.Pos(), field.End()
	if len(field.Names) > 1 {
	start, end = id.Pos(), id.End()
	}
	// This diagnostic carries both an edit-based fix to
	// rename the unused parameter, and a command-based fix
	// to remove it (see golang.RemoveUnusedParameter).
	pass.Report(analysis.Diagnostic{
	Pos: start,
	End: end,
	Message: fmt.Sprintf("unused parameter: %s", id.Name),
	Category: FixCategory,
	SuggestedFixes: []analysis.SuggestedFix{
	{
	Message: `Rename parameter to "_"`,
	TextEdits: []analysis.TextEdit{{
	Pos: id.Pos(),
	End: id.End(),
	NewText: []byte("_"),
	}},
	},
	{
	Message: fmt.Sprintf("Remove unused parameter %q", id.Name),
	// No TextEdits => computed by gopls command
	},
	},
	})
	}
	}
	}

	return true
	})
	return nil, nil
	}