gopls: take control of the flag printing

Add a copy of flag.PrintDefaults so that we can make changes.
This CL does not actually modify anything (although it does have
to detect the private stringValue type a slightly different way)

For #41860

Change-Id: I19512041f9c1bfde56226aea48302cd63cf670e2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/367837
Trust: Ian Cottrell <iancottrell@google.com>
Run-TryBot: Ian Cottrell <iancottrell@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

internal/lsp/cmd/call_hierarchy.go

@@ -32,7 +32,7 @@ Example:
 	$ gopls call_hierarchy helper/helper.go:8:6
 	$ gopls call_hierarchy helper/helper.go:#53
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (c *callHierarchy) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/check.go

@@ -28,7 +28,7 @@ Example: show the diagnostic results of this file:
 
 	$ gopls check internal/lsp/cmd/check.go
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run performs the check on the files specified by args and prints the

internal/lsp/cmd/cmd.go

@@ -15,6 +15,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+	"reflect"
 	"strings"
 	"sync"
 	"text/tabwriter"
@@ -132,7 +133,53 @@ command:
 		fmt.Fprintf(w, "  %s\t%s\n", c.Name(), c.ShortHelp())
 	}
 	fmt.Fprint(w, "\nflags:\n")
-	f.PrintDefaults()
+	printFlagDefaults(f)
+}
+
+// this is a slightly modified version of flag.PrintDefaults to give us control
+func printFlagDefaults(s *flag.FlagSet) {
+	s.VisitAll(func(f *flag.Flag) {
+		var b strings.Builder
+		fmt.Fprintf(&b, "  -%s", f.Name) // Two spaces before -; see next two comments.
+		name, usage := flag.UnquoteUsage(f)
+		if len(name) > 0 {
+			b.WriteString(" ")
+			b.WriteString(name)
+		}
+		// Boolean flags of one ASCII letter are so common we
+		// treat them specially, putting their usage on the same line.
+		if b.Len() <= 4 { // space, space, '-', 'x'.
+			b.WriteString("\t")
+		} else {
+			// Four spaces before the tab triggers good alignment
+			// for both 4- and 8-space tab stops.
+			b.WriteString("\n    \t")
+		}
+		b.WriteString(strings.ReplaceAll(usage, "\n", "\n    \t"))
+		if !isZeroValue(f, f.DefValue) {
+			if reflect.TypeOf(f.Value).Elem().Name() == "stringValue" {
+				fmt.Fprintf(&b, " (default %q)", f.DefValue)
+			} else {
+				fmt.Fprintf(&b, " (default %v)", f.DefValue)
+			}
+		}
+		fmt.Fprint(s.Output(), b.String(), "\n")
+	})
+}
+
+// isZeroValue is copied from the flags package
+func isZeroValue(f *flag.Flag, value string) bool {
+	// Build a zero value of the flag's Value type, and see if the
+	// result of calling its String method equals the value passed in.
+	// This works unless the Value type is itself an interface type.
+	typ := reflect.TypeOf(f.Value)
+	var z reflect.Value
+	if typ.Kind() == reflect.Ptr {
+		z = reflect.New(typ.Elem())
+	} else {
+		z = reflect.Zero(typ)
+	}
+	return value == z.Interface().(flag.Value).String()
 }
 
 // Run takes the args after top level flag processing, and invokes the correct

internal/lsp/cmd/definition.go

@@ -55,7 +55,7 @@ Example: show the definition of the identifier at syntax at offset %[1]v in this
 
 definition-flags:
 `, exampleLine, exampleColumn, exampleOffset)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run performs the definition query as specified by args and prints the

internal/lsp/cmd/folding_range.go

@@ -29,7 +29,7 @@ Example:
 
 	$ gopls folding_ranges helper/helper.go
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (r *foldingRanges) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/format.go

@@ -40,7 +40,7 @@ Example: reformat this file:
 
 format-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run performs the check on the files specified by args and prints the

internal/lsp/cmd/highlight.go

@@ -32,7 +32,7 @@ Example:
 	$ gopls highlight helper/helper.go:8:6
 	$ gopls highlight helper/helper.go:#53
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (r *highlight) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/implementation.go

@@ -32,7 +32,7 @@ Example:
 	$ gopls implementation helper/helper.go:8:6
 	$ gopls implementation helper/helper.go:#53
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (i *implementation) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/imports.go

@@ -38,7 +38,7 @@ Example: update imports statements in a file:
 
 imports-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run performs diagnostic checks on the file specified and either;

internal/lsp/cmd/info.go

@@ -30,7 +30,7 @@ func (v *version) Usage() string     { return "" }
 func (v *version) ShortHelp() string { return "print the gopls version information" }
 func (v *version) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), ``)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run prints version information to stdout.
@@ -50,7 +50,7 @@ func (b *bug) Usage() string     { return "" }
 func (b *bug) ShortHelp() string { return "report a bug in gopls" }
 func (b *bug) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), ``)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 const goplsBugPrefix = "x/tools/gopls: <DESCRIBE THE PROBLEM>"
@@ -98,7 +98,7 @@ func (j *apiJSON) Usage() string     { return "" }
 func (j *apiJSON) ShortHelp() string { return "print json describing gopls API" }
 func (j *apiJSON) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), ``)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (j *apiJSON) Run(ctx context.Context, args ...string) error {
@@ -120,7 +120,7 @@ func (l *licenses) Usage() string     { return "" }
 func (l *licenses) ShortHelp() string { return "print licenses of included software" }
 func (l *licenses) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), ``)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 const licensePreamble = `

internal/lsp/cmd/links.go

@@ -36,7 +36,7 @@ Example: list links contained within a file:
 
 links-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run finds all the links within a document

internal/lsp/cmd/prepare_rename.go

@@ -32,7 +32,7 @@ Example:
 	$ gopls prepare_rename helper/helper.go:8:6
 	$ gopls prepare_rename helper/helper.go:#53
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // ErrInvalidRenamePosition is returned when prepareRename is run at a position that

internal/lsp/cmd/references.go

@@ -36,7 +36,7 @@ Example:
 
 references-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (r *references) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/remote.go

@@ -85,7 +85,7 @@ $ gopls -remote=localhost:8082 remote sessions
 
 func (c *listSessions) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), listSessionsExamples)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (c *listSessions) Run(ctx context.Context, args ...string) error {
@@ -131,7 +131,7 @@ $ gopls -remote=localhost:8082 remote debug localhost:8083
 
 func (c *startDebugging) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), startDebuggingExamples)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (c *startDebugging) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/rename.go

@@ -44,7 +44,7 @@ Example:
 
 rename-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run renames the specified identifier and either;

internal/lsp/cmd/semantictokens.go

@@ -61,7 +61,7 @@ Example: show the semantic tokens for this file:
 
 	$ gopls semtok internal/lsp/cmd/semtok.go
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run performs the semtok on the files specified by args and prints the

internal/lsp/cmd/serve.go

@@ -54,7 +54,7 @@ a child of an editor process.
 
 server-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (s *Serve) remoteArgs(network, address string) []string {

internal/lsp/cmd/signature.go

@@ -31,7 +31,7 @@ Example:
 	$ gopls signature helper/helper.go:8:6
 	$ gopls signature helper/helper.go:#53
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (r *signature) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/subcommands.go

@@ -24,7 +24,7 @@ func (s subcommands) DetailedHelp(f *flag.FlagSet) {
 	for _, c := range s {
 		fmt.Fprintf(w, "  %s\t%s\n", c.Name(), c.ShortHelp())
 	}
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (s subcommands) Usage() string { return "<subcommand> [arg]..." }

internal/lsp/cmd/suggested_fix.go

@@ -38,7 +38,7 @@ Example: apply suggested fixes for this file
 
 fix-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 // Run performs diagnostic checks on the file specified and either;

internal/lsp/cmd/symbols.go

@@ -30,7 +30,7 @@ func (r *symbols) DetailedHelp(f *flag.FlagSet) {
 Example:
 	$ gopls symbols helper/helper.go
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 func (r *symbols) Run(ctx context.Context, args ...string) error {
 	if len(args) != 1 {

internal/lsp/cmd/workspace.go

@@ -51,7 +51,7 @@ func (c *generateWorkspaceMod) ShortHelp() string {
 }
 
 func (c *generateWorkspaceMod) DetailedHelp(f *flag.FlagSet) {
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (c *generateWorkspaceMod) Run(ctx context.Context, args ...string) error {

internal/lsp/cmd/workspace_symbol.go

@@ -33,7 +33,7 @@ Example:
 
 workspace_symbol-flags:
 `)
-	f.PrintDefaults()
+	printFlagDefaults(f)
 }
 
 func (r *workspaceSymbol) Run(ctx context.Context, args ...string) error {