go.chromium.org/luci@v0.0.0-20240309015107-7cdc2e660f33/common/flag/nestedflagset/nestedflagset.go (about)

     1  // Copyright 2016 The LUCI Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package nestedflagset
    16  
    17  import (
    18  	"flag"
    19  	"fmt"
    20  	"strings"
    21  )
    22  
    23  // FlagSet is a flag.Flag implementation that parses into a nested flag.FlagSet.
    24  //
    25  // The FlagSet's flag value is parsed broken into a series of sub-options, which
    26  // are then loaded into the nested flag set (FlagSet.F).
    27  type FlagSet struct {
    28  	F flag.FlagSet // The underlying FlagSet, populated on Parse.
    29  }
    30  
    31  var _ flag.Value = (*FlagSet)(nil)
    32  
    33  // Parse parses a one-line option string into the underlying flag set.
    34  func (fs *FlagSet) Parse(line string) error {
    35  	var args []string
    36  	for _, token := range lexer(line, ',').split() {
    37  		name, value := token.split()
    38  		args = append(args, fmt.Sprintf("-%s", name))
    39  		if value != "" {
    40  			args = append(args, value)
    41  		}
    42  	}
    43  
    44  	return fs.F.Parse(args)
    45  }
    46  
    47  // Usage constructs a one-line usage string for all of the options defined in
    48  // Flags.
    49  func (fs *FlagSet) Usage() string {
    50  	var flags []string
    51  
    52  	// If there is no "help" flag defined, we will use it to display help/usage
    53  	// (default FlagSet).
    54  	if fs.F.Lookup("help") == nil {
    55  		flags = append(flags, "help")
    56  	}
    57  
    58  	fs.F.VisitAll(func(f *flag.Flag) {
    59  		comma := ""
    60  		if len(flags) > 0 {
    61  			comma = ","
    62  		}
    63  		flags = append(flags, fmt.Sprintf("[%s%s]", comma, f.Name))
    64  	})
    65  	return strings.Join(flags, "")
    66  }
    67  
    68  // Set implements flags.Value.
    69  func (fs *FlagSet) Set(value string) error {
    70  	return fs.Parse(value)
    71  }
    72  
    73  // String implements flags.Value.
    74  func (fs *FlagSet) String() string {
    75  	return fs.Usage()
    76  }