proposal: flag: option to accept abbreviations of flags

[KarelKubat]

gopls version

Build info

golang.org/x/tools/gopls v0.8.4
golang.org/x/tools/gopls@v0.8.4 h1:zGZsAXAb0LLws/Z+2BCWR17dkPHhIO2GYwYSSkeXX5c=
github.com/BurntSushi/toml@v1.0.0 h1:dtDWrepsVPfW9H/4y7dDgFc2MBUSeJhlaDtK13CxFlU=
github.com/google/go-cmp@v0.5.7 h1:81/ik6ipDQS2aGcBfIN5dHDB36BwrStyeAQquSYCV4o=
github.com/sergi/go-diff@v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
golang.org/x/exp/typeparams@v0.0.0-20220218215828-6cf2b201936e h1:qyrTQ++p1afMkO4DPEeLGq/3oTsdlvdH4vqZUBWzUKM=
golang.org/x/mod@v0.6.0-dev.0.20220419223038-86c51ed26bb4 h1:6zppjxzCulZykYSLyVDYbneBfbaBIQPYMevg0bEwv2s=
golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c h1:5KslGYwFpkhGh+Q16bwMP3cOontH8FOep7tGV86Y7SQ=
golang.org/x/sys@v0.0.0-20220209214540-3681064d5158 h1:rm+CHSpPEEW2IsXUib1ThaHIjuBVZjxNgSKmBLFfD4c=
golang.org/x/text@v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
golang.org/x/tools@v0.1.11-0.20220513164230-dfee1649af67 h1:CJwk4qG1fov4WP7/DWhhb7OQVZlQKAl1rEMnDF+ceGU=
golang.org/x/vuln@v0.0.0-20220503210553-a5481fb0c8be h1:jokAF1mfylAi1iTQx7C44B7vyXUcSEMw8eDv0PzNu8s=
honnef.co/go/tools@v0.3.0 h1:2LdYUZ7CIxnYgskbUZfY7FPggmqnh6shBqfWa8Tn3XU=
mvdan.cc/gofumpt@v0.3.0 h1:kTojdZo9AcEYbQYhGuLf/zszYthRdhDNDUi2JKTxas4=
mvdan.cc/xurls/v2@v2.4.0 h1:tzxjVAj+wSBmDcF6zBB7/myTy3gX9xvi8Tyr28AuQgc=
go: go1.18

go env

GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/karelk/Library/Caches/go-build"
GOENV="/Users/karelk/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/karelk/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/karelk/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/local/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/local/lib/go/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.18.2"
GCCGO="gccgo"
AR="ar"
CC="/usr/bin/clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/c8/27sy8g9d47ngtrxhb_x34nkw00_w91/T/go-build943201535=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

• Defining flags using the flag package often leads to long flag names.

What did you expect to see?

• The flag package should automatically recognize shorthands where possible.
• Example: if a flag.FlagSet (which may be the global flag.CommandLine) holds the flags: verbose and length then automagically an invocation with -v and -l should work.
  • The package should resolve -v to the defined flag verbose and -l to the length.
  • Arbitrary lengths should be possible: -ver and -len should also resolve to verbose and length.
  • Only when a name can't be uniquely resolved to an existing flag, should an error be raised.
• For ambiguous names the flags should be shortened until they are unique. E.g., defined flags item and id couldn't be abbreviated to -i, but instead to -it and -id.

What did you see instead?

The standard way that package flag works is that upon invocation, an error occurs that flag -i is given but not defined. It would be better if the package tried to resolve the flag in the set of defined names.

Implementation thoughts

I wrote a functional mockup at https://github.com/KarelKubat/flagnames. This has the drawback that the arguments that are passed into flag.Parse() are patched from abbreviated forms into whatever flags are defined. That works fine, but isn't too elegant.

A better approach would be to:

• Define a bool acceptAbbrevs in the FlagSet structure, defaulting to false to keep parity with the existing way,
• Provide accessors (per-FlagSet and global), e.g. flag.AcceptAbbrevs()
• When the bool is set, resolve provided flags against defined names while allowing abbreviations
• Only issue an error when a provided flag:
  • Doesn't occur as a prefix in any defined flag name
  • Could resolve to multiple defined flags

A hypothetical code sample:

var verboseFlag = flag.Bool("verbose", false, "increases verbosity")
flag.AcceptAbbrevs().  // allow -v, -ve, -ver, -verb etc.
flag.Parse()

My Question

Your thoughts?

• I'm happy to propose this change to package flag.
• But if you think it's not worth while then please let me know and I'll happily continue using github.com/KarelKubat/flagnames to scratch my itch.

[seankhliao]

Duplicate of #40138