gopls/internal/util/moreslices: add Reversed iterator

..and use it throughout gopls.

Change-Id: Ic59129b521f98865e4d14bcb4a6a326ee0f8886a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/680435
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

Author: adonovan

gopls/internal/analysis/infertypeargs/infertypeargs.go

@@ -12,6 +12,7 @@ import (
 	"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/typeparams"
 )
 
@@ -74,7 +75,7 @@ func diagnose(fset *token.FileSet, inspect *inspector.Inspector, start, end toke
 		// Start removing argument expressions from the right, and check if we can
 		// still infer the call expression.
 		required := len(indices) // number of type expressions that are required
-		for i := len(indices) - 1; i >= 0; i-- {
+		for i, _ := range moreslices.Reversed(indices) {
 			var fun ast.Expr
 			if i == 0 {
 				// No longer an index expression: just use the parameterized operand.

gopls/internal/cache/check.go

@@ -34,6 +34,7 @@ import (
 	"golang.org/x/tools/gopls/internal/protocol"
 	"golang.org/x/tools/gopls/internal/util/bug"
 	"golang.org/x/tools/gopls/internal/util/moremaps"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/internal/analysisinternal"
 	"golang.org/x/tools/internal/event"
@@ -1870,8 +1871,7 @@ func depsErrors(ctx context.Context, snapshot *Snapshot, mp *metadata.Package) (
 	// we reach the workspace.
 	var errors []*Diagnostic
 	for _, depErr := range relevantErrors {
-		for i := len(depErr.ImportStack) - 1; i >= 0; i-- {
-			item := depErr.ImportStack[i]
+		for _, item := range moreslices.Reversed(depErr.ImportStack) {
 			if snapshot.IsWorkspacePackage(PackageID(item)) {
 				break
 			}
@@ -1909,8 +1909,7 @@ func depsErrors(ctx context.Context, snapshot *Snapshot, mp *metadata.Package) (
 	// Add a diagnostic to the module that contained the lowest-level import of
 	// the missing package.
 	for _, depErr := range relevantErrors {
-		for i := len(depErr.ImportStack) - 1; i >= 0; i-- {
-			item := depErr.ImportStack[i]
+		for _, item := range moreslices.Reversed(depErr.ImportStack) {
 			mp := snapshot.Metadata(PackageID(item))
 			if mp == nil || mp.Module == nil {
 				continue

gopls/internal/cache/mod.go

@@ -18,6 +18,7 @@ import (
 	"golang.org/x/tools/gopls/internal/label"
 	"golang.org/x/tools/gopls/internal/protocol"
 	"golang.org/x/tools/gopls/internal/protocol/command"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/memoize"
 )
@@ -380,8 +381,8 @@ func (s *Snapshot) matchErrorToModule(pm *ParsedModule, goCmdError string) (prot
 	var reference *modfile.Line
 	matches := moduleVersionInErrorRe.FindAllStringSubmatch(goCmdError, -1)
 
-	for i := len(matches) - 1; i >= 0; i-- {
-		ver := module.Version{Path: matches[i][1], Version: matches[i][2]}
+	for _, match := range moreslices.Reversed(matches) {
+		ver := module.Version{Path: match[1], Version: match[2]}
 		if err := module.Check(ver.Path, ver.Version); err != nil {
 			continue
 		}
@@ -412,8 +413,8 @@ func (s *Snapshot) matchErrorToModule(pm *ParsedModule, goCmdError string) (prot
 func (s *Snapshot) goCommandDiagnostic(pm *ParsedModule, loc protocol.Location, goCmdError string) (*Diagnostic, error) {
 	matches := moduleVersionInErrorRe.FindAllStringSubmatch(goCmdError, -1)
 	var innermost *module.Version
-	for i := len(matches) - 1; i >= 0; i-- {
-		ver := module.Version{Path: matches[i][1], Version: matches[i][2]}
+	for _, match := range moreslices.Reversed(matches) {
+		ver := module.Version{Path: match[1], Version: match[2]}
 		if err := module.Check(ver.Path, ver.Version); err != nil {
 			continue
 		}

gopls/internal/cmd/semantictokens.go

@@ -16,6 +16,7 @@ import (
 	"golang.org/x/tools/gopls/internal/protocol"
 	"golang.org/x/tools/gopls/internal/protocol/semtok"
 	"golang.org/x/tools/gopls/internal/settings"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 )
 
 // generate semantic tokens and interpolate them in the file
@@ -147,8 +148,7 @@ func decorate(legend protocol.SemanticTokensLegend, file *cmdFile, data []uint32
 		return nil
 	}
 	lines := bytes.Split(file.mapper.Content, []byte{'\n'})
-	for i := len(marks) - 1; i >= 0; i-- {
-		mx := marks[i]
+	for _, mx := range moreslices.Reversed(marks) {
 		markLine(mx, lines)
 	}
 	os.Stdout.Write(bytes.Join(lines, []byte{'\n'}))

gopls/internal/golang/completion/util.go

@@ -12,6 +12,7 @@ import (
 	"golang.org/x/tools/go/types/typeutil"
 	"golang.org/x/tools/gopls/internal/golang"
 	"golang.org/x/tools/gopls/internal/protocol"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/internal/diff"
 	"golang.org/x/tools/internal/typeparams"
@@ -271,9 +272,9 @@ func prevStmt(pos token.Pos, path []ast.Node) ast.Stmt {
 		}
 	}
 
-	for i := len(blockLines) - 1; i >= 0; i-- {
-		if blockLines[i].End() < pos {
-			return blockLines[i]
+	for _, line := range moreslices.Reversed(blockLines) {
+		if line.End() < pos {
+			return line
 		}
 	}
 

gopls/internal/golang/extract.go

@@ -26,6 +26,7 @@ import (
 	"golang.org/x/tools/gopls/internal/cache/parsego"
 	goplsastutil "golang.org/x/tools/gopls/internal/util/astutil"
 	"golang.org/x/tools/gopls/internal/util/bug"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/internal/typesinternal"
 )
@@ -2115,8 +2116,7 @@ func isFreeBranchStmt(stack []ast.Node) bool {
 			}
 		case token.BREAK, token.CONTINUE:
 			// Find innermost relevant ancestor for break/continue.
-			for i := len(stack) - 2; i >= 0; i-- {
-				n := stack[i]
+			for _, n := range moreslices.Reversed(stack) {
 				if isLabeled {
 					l, ok := n.(*ast.LabeledStmt)
 					if !(ok && l.Label.Name == node.Label.Name) {

gopls/internal/golang/hover.go

@@ -37,6 +37,7 @@ import (
 	"golang.org/x/tools/gopls/internal/settings"
 	gastutil "golang.org/x/tools/gopls/internal/util/astutil"
 	"golang.org/x/tools/gopls/internal/util/bug"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	internalastutil "golang.org/x/tools/internal/astutil"
 	"golang.org/x/tools/internal/event"
@@ -1561,8 +1562,8 @@ func findDeclInfo(files []*ast.File, pos token.Pos) (decl ast.Decl, spec ast.Spe
 		switch n := n.(type) {
 		case *ast.Field:
 			findEnclosingDeclAndSpec := func() {
-				for i := len(stack) - 1; i >= 0; i-- {
-					switch n := stack[i].(type) {
+				for _, n := range moreslices.Reversed(stack) {
+					switch n := n.(type) {
 					case ast.Spec:
 						spec = n
 					case ast.Decl:

gopls/internal/golang/semtok.go

@@ -29,6 +29,7 @@ import (
 	"golang.org/x/tools/gopls/internal/protocol"
 	"golang.org/x/tools/gopls/internal/protocol/semtok"
 	"golang.org/x/tools/gopls/internal/util/bug"
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/internal/astutil"
 	"golang.org/x/tools/internal/event"
@@ -277,8 +278,7 @@ func (tv *tokenVisitor) token(start token.Pos, length int, typ semtok.Type, modi
 // strStack converts the stack to a string, for debugging and error messages.
 func (tv *tokenVisitor) strStack() string {
 	msg := []string{"["}
-	for i := len(tv.stack) - 1; i >= 0; i-- {
-		n := tv.stack[i]
+	for _, n := range moreslices.Reversed(tv.stack) {
 		msg = append(msg, strings.TrimPrefix(fmt.Sprintf("%T", n), "*ast."))
 	}
 	if len(tv.stack) > 0 {
@@ -649,8 +649,8 @@ func (tv *tokenVisitor) ident(id *ast.Ident) {
 // isParam reports whether the position is that of a parameter name of
 // an enclosing function.
 func (tv *tokenVisitor) isParam(pos token.Pos) bool {
-	for i := len(tv.stack) - 1; i >= 0; i-- {
-		switch n := tv.stack[i].(type) {
+	for _, n := range moreslices.Reversed(tv.stack) {
+		switch n := n.(type) {
 		case *ast.FuncDecl:
 			for _, f := range n.Type.Params.List {
 				for _, id := range f.Names {

gopls/internal/server/general.go

@@ -284,13 +284,11 @@ func (s *server) checkViewGoVersions() {
 // version, it returns -1.
 //
 // Copied from the testenv package.
-func go1Point() int {
-	for i := len(build.Default.ReleaseTags) - 1; i >= 0; i-- {
-		var version int
-		if _, err := fmt.Sscanf(build.Default.ReleaseTags[i], "go1.%d", &version); err != nil {
-			continue
+func go1Point() (version int) {
+	for _, tag := range moreslices.Reversed(build.Default.ReleaseTags) {
+		if _, err := fmt.Sscanf(tag, "go1.%d", &version); err == nil {
+			return
 		}
-		return version
 	}
 	return -1
 }

gopls/internal/template/parse_test.go

@@ -7,6 +7,8 @@ package template
 import (
 	"strings"
 	"testing"
+
+	"golang.org/x/tools/gopls/internal/util/moreslices"
 )
 
 type datum struct {
@@ -135,8 +137,7 @@ func TestLineCol(t *testing.T) {
 			t.Errorf("expected %d, %d, got %d, %d for case %d", len(lines)-1, mxlen, lastl, lastc, n)
 		}
 		// backwards
-		for j := len(saved) - 1; j >= 0; j-- {
-			s := saved[j]
+		for j, s := range moreslices.Reversed(saved) {
 			xl, xc := p.LineCol(s.offset)
 			if xl != s.l || xc != s.c {
 				t.Errorf("at offset %d(%d), got (%d,%d), expected (%d,%d)", s.offset, j, xl, xc, s.l, s.c)