internal/lsp/source/completion/statements.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 completion

 import (
 	"fmt"
 	"go/ast"
 	"go/token"
 	"go/types"

 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/snippet"
 	"golang.org/x/tools/internal/lsp/source"
 )

 // addStatementCandidates adds full statement completion candidates
 // appropriate for the current context.
 func (c *completer) addStatementCandidates() {
 	c.addErrCheck()
 	c.addAssignAppend()
 }

 // addAssignAppend offers a completion candidate of the form:
 //
 //     someSlice = append(someSlice, )
 //
 // It will offer the "append" completion in two situations:
 //
 // 1. Position is in RHS of assign, prefix matches "append", and
 //    corresponding LHS object is a slice. For example,
 //    "foo = ap<>" completes to "foo = append(foo, )".
 //
 // Or
 //
 // 2. Prefix is an ident or selector in an *ast.ExprStmt (i.e.
 //    beginning of statement), and our best matching candidate is a
 //    slice. For example: "foo.ba" completes to "foo.bar = append(foo.bar, )".
 func (c *completer) addAssignAppend() {
 	if len(c.path) < 3 {
 		return
 	}

 	ident, _ := c.path[0].(*ast.Ident)
 	if ident == nil {
 		return
 	}

 	var (
 		// sliceText is the full name of our slice object, e.g. "s.abc" in
 		// "s.abc = app<>".
 		sliceText string
 		// needsLHS is true if we need to prepend the LHS slice name and
 		// "=" to our candidate.
 		needsLHS = false
 		fset     = c.snapshot.FileSet()
 	)

 	switch n := c.path[1].(type) {
 	case *ast.AssignStmt:
 		// We are already in an assignment. Make sure our prefix matches "append".
 		if c.matcher.Score("append") <= 0 {
 			return
 		}

 		exprIdx := exprAtPos(c.pos, n.Rhs)
 		if exprIdx == len(n.Rhs) || exprIdx > len(n.Lhs)-1 {
 			return
 		}

 		lhsType := c.pkg.GetTypesInfo().TypeOf(n.Lhs[exprIdx])
 		if lhsType == nil {
 			return
 		}

 		// Make sure our corresponding LHS object is a slice.
 		if _, isSlice := lhsType.Underlying().(*types.Slice); !isSlice {
 			return
 		}

 		// The name or our slice is whatever's in the LHS expression.
 		sliceText = source.FormatNode(fset, n.Lhs[exprIdx])
 	case *ast.SelectorExpr:
 		// Make sure we are a selector at the beginning of a statement.
 		if _, parentIsExprtStmt := c.path[2].(*ast.ExprStmt); !parentIsExprtStmt {
 			return
 		}

 		// So far we only know the first part of our slice name. For
 		// example in "s.a<>" we only know our slice begins with "s."
 		// since the user could still be typing.
 		sliceText = source.FormatNode(fset, n.X) + "."
 		needsLHS = true
 	case *ast.ExprStmt:
 		needsLHS = true
 	default:
 		return
 	}

 	var (
 		label string
 		snip  snippet.Builder
 		score = highScore
 	)

 	if needsLHS {
 		// Offer the long form assign + append candidate if our best
 		// candidate is a slice.
 		bestItem := c.topCandidate()
 		if bestItem == nil || bestItem.obj == nil || bestItem.obj.Type() == nil {
 			return
 		}

 		if _, isSlice := bestItem.obj.Type().Underlying().(*types.Slice); !isSlice {
 			return
 		}

 		// Don't rank the full form assign + append candidate above the
 		// slice itself.
 		score = bestItem.Score - 0.01

 		// Fill in rest of sliceText now that we have the object name.
 		sliceText += bestItem.Label

 		// Fill in the candidate's LHS bits.
 		label = fmt.Sprintf("%s = ", bestItem.Label)
 		snip.WriteText(label)
 	}

 	snip.WriteText(fmt.Sprintf("append(%s, ", sliceText))
 	snip.WritePlaceholder(nil)
 	snip.WriteText(")")

 	c.items = append(c.items, CompletionItem{
 		Label:   label + fmt.Sprintf("append(%s, )", sliceText),
 		Kind:    protocol.FunctionCompletion,
 		Score:   score,
 		snippet: &snip,
 	})
 }

 // topCandidate returns the strictly highest scoring candidate
 // collected so far. If the top two candidates have the same score,
 // nil is returned.
 func (c *completer) topCandidate() *CompletionItem {
 	var bestItem, secondBestItem *CompletionItem
 	for i := range c.items {
 		if bestItem == nil || c.items[i].Score > bestItem.Score {
 			bestItem = &c.items[i]
 		} else if secondBestItem == nil || c.items[i].Score > secondBestItem.Score {
 			secondBestItem = &c.items[i]
 		}
 	}

 	// If secondBestItem has the same score, bestItem isn't
 	// the strict best.
 	if secondBestItem != nil && secondBestItem.Score == bestItem.Score {
 		return nil
 	}

 	return bestItem
 }

 // addErrCheck offers a completion candidate of the form:
 //
 //     if err != nil {
 //       return nil, err
 //     }
 //
 // In the case of test functions, it offers a completion candidate of the form:
 //
 //     if err != nil {
 //       t.Fatal(err)
 //     }
 //
 // The position must be in a function that returns an error, and the
 // statement preceding the position must be an assignment where the
 // final LHS object is an error. addErrCheck will synthesize
 // zero values as necessary to make the return statement valid.
 func (c *completer) addErrCheck() {
 	if len(c.path) < 2 || c.enclosingFunc == nil || !c.opts.placeholders {
 		return
 	}

 	var (
 		errorType        = types.Universe.Lookup("error").Type()
 		result           = c.enclosingFunc.sig.Results()
 		testVar          = getTestVar(c.enclosingFunc, c.pkg)
 		isTest           = testVar != ""
 		doesNotReturnErr = result.Len() == 0 || !types.Identical(result.At(result.Len()-1).Type(), errorType)
 	)
 	// Make sure our enclosing function is a Test func or returns an error.
 	if !isTest && doesNotReturnErr {
 		return
 	}

 	prevLine := prevStmt(c.pos, c.path)
 	if prevLine == nil {
 		return
 	}

 	// Make sure our preceding statement was as assignment.
 	assign, _ := prevLine.(*ast.AssignStmt)
 	if assign == nil || len(assign.Lhs) == 0 {
 		return
 	}

 	lastAssignee := assign.Lhs[len(assign.Lhs)-1]

 	// Make sure the final assignee is an error.
 	if !types.Identical(c.pkg.GetTypesInfo().TypeOf(lastAssignee), errorType) {
 		return
 	}

 	var (
 		// errVar is e.g. "err" in "foo, err := bar()".
 		errVar = source.FormatNode(c.snapshot.FileSet(), lastAssignee)

 		// Whether we need to include the "if" keyword in our candidate.
 		needsIf = true
 	)

 	// If the returned error from the previous statement is "_", it is not a real object.
 	// If we don't have an error, and the function signature takes a testing.TB that is either ignored
 	// or an "_", then we also can't call t.Fatal(err).
 	if errVar == "_" {
 		return
 	}

 	// Below we try to detect if the user has already started typing "if
 	// err" so we can replace what they've typed with our complete
 	// statement.
 	switch n := c.path[0].(type) {
 	case *ast.Ident:
 		switch c.path[1].(type) {
 		case *ast.ExprStmt:
 			// This handles:
 			//
 			//     f, err := os.Open("foo")
 			//     i<>

 			// Make sure they are typing "if".
 			if c.matcher.Score("if") <= 0 {
 				return
 			}
 		case *ast.IfStmt:
 			// This handles:
 			//
 			//     f, err := os.Open("foo")
 			//     if er<>

 			// Make sure they are typing the error's name.
 			if c.matcher.Score(errVar) <= 0 {
 				return
 			}

 			needsIf = false
 		default:
 			return
 		}
 	case *ast.IfStmt:
 		// This handles:
 		//
 		//     f, err := os.Open("foo")
 		//     if <>

 		// Avoid false positives by ensuring the if's cond is a bad
 		// expression. For example, don't offer the completion in cases
 		// like "if <> somethingElse".
 		if _, bad := n.Cond.(*ast.BadExpr); !bad {
 			return
 		}

 		// If "if" is our direct prefix, we need to include it in our
 		// candidate since the existing "if" will be overwritten.
 		needsIf = c.pos == n.Pos()+token.Pos(len("if"))
 	}

 	// Build up a snippet that looks like:
 	//
 	//     if err != nil {
 	//       return <zero value>, ..., ${1:err}
 	//     }
 	//
 	// We make the error a placeholder so it is easy to alter the error.
 	var snip snippet.Builder
 	if needsIf {
 		snip.WriteText("if ")
 	}
 	snip.WriteText(fmt.Sprintf("%s != nil {\n\t", errVar))

 	var label string
 	if isTest {
 		snip.WriteText(fmt.Sprintf("%s.Fatal(%s)", testVar, errVar))
 		label = fmt.Sprintf("%[1]s != nil { %[2]s.Fatal(%[1]s) }", errVar, testVar)
 	} else {
 		snip.WriteText("return ")
 		for i := 0; i < result.Len()-1; i++ {
 			snip.WriteText(formatZeroValue(result.At(i).Type(), c.qf))
 			snip.WriteText(", ")
 		}
 		snip.WritePlaceholder(func(b *snippet.Builder) {
 			b.WriteText(errVar)
 		})
 		label = fmt.Sprintf("%[1]s != nil { return %[1]s }", errVar)
 	}

 	snip.WriteText("\n}")

 	if needsIf {
 		label = "if " + label
 	}

 	c.items = append(c.items, CompletionItem{
 		Label: label,
 		// There doesn't seem to be a more appropriate kind.
 		Kind:    protocol.KeywordCompletion,
 		Score:   highScore,
 		snippet: &snip,
 	})
 }

 // getTestVar checks the function signature's input parameters and returns
 // the name of the first parameter that implements "testing.TB". For example,
 // func someFunc(t *testing.T) returns the string "t", func someFunc(b *testing.B)
 // returns "b" etc. An empty string indicates that the function signature
 // does not take a testing.TB parameter or does so but is ignored such
 // as func someFunc(*testing.T).
 func getTestVar(enclosingFunc *funcInfo, pkg source.Package) string {
 	if enclosingFunc == nil || enclosingFunc.sig == nil {
 		return ""
 	}

 	sig := enclosingFunc.sig
 	for i := 0; i < sig.Params().Len(); i++ {
 		param := sig.Params().At(i)
 		if param.Name() == "_" {
 			continue
 		}
 		testingPkg, err := pkg.GetImport("testing")
 		if err != nil {
 			continue
 		}
 		tbObj := testingPkg.GetTypes().Scope().Lookup("TB")
 		if tbObj == nil {
 			continue
 		}
 		iface, ok := tbObj.Type().Underlying().(*types.Interface)
 		if !ok {
 			continue
 		}
 		if !types.Implements(param.Type(), iface) {
 			continue
 		}
 		return param.Name()
 	}

 	return ""
 }
	// 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 completion

	import (
	"fmt"
	"go/ast"
	"go/token"
	"go/types"

	"golang.org/x/tools/internal/lsp/protocol"
	"golang.org/x/tools/internal/lsp/snippet"
	"golang.org/x/tools/internal/lsp/source"
	)

	// addStatementCandidates adds full statement completion candidates
	// appropriate for the current context.
	func (c *completer) addStatementCandidates() {
	c.addErrCheck()
	c.addAssignAppend()
	}

	// addAssignAppend offers a completion candidate of the form:
	//
	// someSlice = append(someSlice, )
	//
	// It will offer the "append" completion in two situations:
	//
	// 1. Position is in RHS of assign, prefix matches "append", and
	// corresponding LHS object is a slice. For example,
	// "foo = ap<>" completes to "foo = append(foo, )".
	//
	// Or
	//
	// 2. Prefix is an ident or selector in an *ast.ExprStmt (i.e.
	// beginning of statement), and our best matching candidate is a
	// slice. For example: "foo.ba" completes to "foo.bar = append(foo.bar, )".
	func (c *completer) addAssignAppend() {
	if len(c.path) < 3 {
	return
	}

	ident, _ := c.path[0].(*ast.Ident)
	if ident == nil {
	return
	}

	var (
	// sliceText is the full name of our slice object, e.g. "s.abc" in
	// "s.abc = app<>".
	sliceText string
	// needsLHS is true if we need to prepend the LHS slice name and
	// "=" to our candidate.
	needsLHS = false
	fset = c.snapshot.FileSet()
	)

	switch n := c.path[1].(type) {
	case *ast.AssignStmt:
	// We are already in an assignment. Make sure our prefix matches "append".
	if c.matcher.Score("append") <= 0 {
	return
	}

	exprIdx := exprAtPos(c.pos, n.Rhs)
	if exprIdx == len(n.Rhs) \|\| exprIdx > len(n.Lhs)-1 {
	return
	}

	lhsType := c.pkg.GetTypesInfo().TypeOf(n.Lhs[exprIdx])
	if lhsType == nil {
	return
	}

	// Make sure our corresponding LHS object is a slice.
	if _, isSlice := lhsType.Underlying().(*types.Slice); !isSlice {
	return
	}

	// The name or our slice is whatever's in the LHS expression.
	sliceText = source.FormatNode(fset, n.Lhs[exprIdx])
	case *ast.SelectorExpr:
	// Make sure we are a selector at the beginning of a statement.
	if _, parentIsExprtStmt := c.path[2].(*ast.ExprStmt); !parentIsExprtStmt {
	return
	}

	// So far we only know the first part of our slice name. For
	// example in "s.a<>" we only know our slice begins with "s."
	// since the user could still be typing.
	sliceText = source.FormatNode(fset, n.X) + "."
	needsLHS = true
	case *ast.ExprStmt:
	needsLHS = true
	default:
	return
	}

	var (
	label string
	snip snippet.Builder
	score = highScore
	)

	if needsLHS {
	// Offer the long form assign + append candidate if our best
	// candidate is a slice.
	bestItem := c.topCandidate()
	if bestItem == nil \|\| bestItem.obj == nil \|\| bestItem.obj.Type() == nil {
	return
	}

	if _, isSlice := bestItem.obj.Type().Underlying().(*types.Slice); !isSlice {
	return
	}

	// Don't rank the full form assign + append candidate above the
	// slice itself.
	score = bestItem.Score - 0.01

	// Fill in rest of sliceText now that we have the object name.
	sliceText += bestItem.Label

	// Fill in the candidate's LHS bits.
	label = fmt.Sprintf("%s = ", bestItem.Label)
	snip.WriteText(label)
	}

	snip.WriteText(fmt.Sprintf("append(%s, ", sliceText))
	snip.WritePlaceholder(nil)
	snip.WriteText(")")

	c.items = append(c.items, CompletionItem{
	Label: label + fmt.Sprintf("append(%s, )", sliceText),
	Kind: protocol.FunctionCompletion,
	Score: score,
	snippet: &snip,
	})
	}

	// topCandidate returns the strictly highest scoring candidate
	// collected so far. If the top two candidates have the same score,
	// nil is returned.
	func (c completer) topCandidate() CompletionItem {
	var bestItem, secondBestItem *CompletionItem
	for i := range c.items {
	if bestItem == nil \|\| c.items[i].Score > bestItem.Score {
	bestItem = &c.items[i]
	} else if secondBestItem == nil \|\| c.items[i].Score > secondBestItem.Score {
	secondBestItem = &c.items[i]
	}
	}

	// If secondBestItem has the same score, bestItem isn't
	// the strict best.
	if secondBestItem != nil && secondBestItem.Score == bestItem.Score {
	return nil
	}

	return bestItem
	}

	// addErrCheck offers a completion candidate of the form:
	//
	// if err != nil {
	// return nil, err
	// }
	//
	// In the case of test functions, it offers a completion candidate of the form:
	//
	// if err != nil {
	// t.Fatal(err)
	// }
	//
	// The position must be in a function that returns an error, and the
	// statement preceding the position must be an assignment where the
	// final LHS object is an error. addErrCheck will synthesize
	// zero values as necessary to make the return statement valid.
	func (c *completer) addErrCheck() {
	if len(c.path) < 2 \|\| c.enclosingFunc == nil \|\| !c.opts.placeholders {
	return
	}

	var (
	errorType = types.Universe.Lookup("error").Type()
	result = c.enclosingFunc.sig.Results()
	testVar = getTestVar(c.enclosingFunc, c.pkg)
	isTest = testVar != ""
	doesNotReturnErr = result.Len() == 0 \|\| !types.Identical(result.At(result.Len()-1).Type(), errorType)
	)
	// Make sure our enclosing function is a Test func or returns an error.
	if !isTest && doesNotReturnErr {
	return
	}

	prevLine := prevStmt(c.pos, c.path)
	if prevLine == nil {
	return
	}

	// Make sure our preceding statement was as assignment.
	assign, _ := prevLine.(*ast.AssignStmt)
	if assign == nil \|\| len(assign.Lhs) == 0 {
	return
	}

	lastAssignee := assign.Lhs[len(assign.Lhs)-1]

	// Make sure the final assignee is an error.
	if !types.Identical(c.pkg.GetTypesInfo().TypeOf(lastAssignee), errorType) {
	return
	}

	var (
	// errVar is e.g. "err" in "foo, err := bar()".
	errVar = source.FormatNode(c.snapshot.FileSet(), lastAssignee)

	// Whether we need to include the "if" keyword in our candidate.
	needsIf = true
	)

	// If the returned error from the previous statement is "_", it is not a real object.
	// If we don't have an error, and the function signature takes a testing.TB that is either ignored
	// or an "_", then we also can't call t.Fatal(err).
	if errVar == "_" {
	return
	}

	// Below we try to detect if the user has already started typing "if
	// err" so we can replace what they've typed with our complete
	// statement.
	switch n := c.path[0].(type) {
	case *ast.Ident:
	switch c.path[1].(type) {
	case *ast.ExprStmt:
	// This handles:
	//
	// f, err := os.Open("foo")
	// i<>

	// Make sure they are typing "if".
	if c.matcher.Score("if") <= 0 {
	return
	}
	case *ast.IfStmt:
	// This handles:
	//
	// f, err := os.Open("foo")
	// if er<>

	// Make sure they are typing the error's name.
	if c.matcher.Score(errVar) <= 0 {
	return
	}

	needsIf = false
	default:
	return
	}
	case *ast.IfStmt:
	// This handles:
	//
	// f, err := os.Open("foo")
	// if <>

	// Avoid false positives by ensuring the if's cond is a bad
	// expression. For example, don't offer the completion in cases
	// like "if <> somethingElse".
	if _, bad := n.Cond.(*ast.BadExpr); !bad {
	return
	}

	// If "if" is our direct prefix, we need to include it in our
	// candidate since the existing "if" will be overwritten.
	needsIf = c.pos == n.Pos()+token.Pos(len("if"))
	}

	// Build up a snippet that looks like:
	//
	// if err != nil {
	// return <zero value>, ..., ${1:err}
	// }
	//
	// We make the error a placeholder so it is easy to alter the error.
	var snip snippet.Builder
	if needsIf {
	snip.WriteText("if ")
	}
	snip.WriteText(fmt.Sprintf("%s != nil {\n\t", errVar))

	var label string
	if isTest {
	snip.WriteText(fmt.Sprintf("%s.Fatal(%s)", testVar, errVar))
	label = fmt.Sprintf("%[1]s != nil { %[2]s.Fatal(%[1]s) }", errVar, testVar)
	} else {
	snip.WriteText("return ")
	for i := 0; i < result.Len()-1; i++ {
	snip.WriteText(formatZeroValue(result.At(i).Type(), c.qf))
	snip.WriteText(", ")
	}
	snip.WritePlaceholder(func(b *snippet.Builder) {
	b.WriteText(errVar)
	})
	label = fmt.Sprintf("%[1]s != nil { return %[1]s }", errVar)
	}

	snip.WriteText("\n}")

	if needsIf {
	label = "if " + label
	}

	c.items = append(c.items, CompletionItem{
	Label: label,
	// There doesn't seem to be a more appropriate kind.
	Kind: protocol.KeywordCompletion,
	Score: highScore,
	snippet: &snip,
	})
	}

	// getTestVar checks the function signature's input parameters and returns
	// the name of the first parameter that implements "testing.TB". For example,
	// func someFunc(t testing.T) returns the string "t", func someFunc(b testing.B)
	// returns "b" etc. An empty string indicates that the function signature
	// does not take a testing.TB parameter or does so but is ignored such
	// as func someFunc(*testing.T).
	func getTestVar(enclosingFunc *funcInfo, pkg source.Package) string {
	if enclosingFunc == nil \|\| enclosingFunc.sig == nil {
	return ""
	}

	sig := enclosingFunc.sig
	for i := 0; i < sig.Params().Len(); i++ {
	param := sig.Params().At(i)
	if param.Name() == "_" {
	continue
	}
	testingPkg, err := pkg.GetImport("testing")
	if err != nil {
	continue
	}
	tbObj := testingPkg.GetTypes().Scope().Lookup("TB")
	if tbObj == nil {
	continue
	}
	iface, ok := tbObj.Type().Underlying().(*types.Interface)
	if !ok {
	continue
	}
	if !types.Implements(param.Type(), iface) {
	continue
	}
	return param.Name()
	}

	return ""
	}