cli, completion: compress some const strings (#652)

This uses `supersnappy` [1], which is a zero-dependency pure-Nim
implementation of Google's Snappy [2].

With it, it is straightforward to compress our larger `const` strings
at compile time and uncompress them at run time. For now, this commit
compresses:

- The `configlet --help` message
- The completion scripts

`supersnappy` is less than 500 lines of code, which is why compressing
these strings (which aren't so large) produces a slightly smaller
configlet binary, despite the added dependency.

We may end up adding `zippy` [3] as a dependency if configlet learns
to make network requests (e.g. for the online `configlet lint` checks)
so that we can use gzip. But we can't use `zippy` at compile time, so it
isn't useful for this commit, even though the compression is better.
`zippy` is also a bigger dependency (about 40 KiB), so it wouldn't
produce a net saving for this commit anyway.

`nim-snappy` [4] is an alternative Snappy implementation, but it would
add dependencies [5] on `faststreams`, `unittest2`, and `stew`.

[1] https://github.com/guzba/supersnappy
[2] https://github.com/google/snappy
[3] https://github.com/guzba/zippy
[4] https://github.com/status-im/nim-snappy
[5] https://github.com/status-im/nim-snappy/blob/7cb2e57a5861/snappy.nimble

Closes: #651

configlet.nimble

@@ -19,18 +19,19 @@ bin           = @["configlet"]
 
 # Dependencies
 requires "nim >= 1.6.6"
-requires "cligen#b962cf8bc0be847cbc1b4f77952775de765e9689"    # 1.5.19 (2021-09-13)
-requires "jsony#2a2cc4331720b7695c8b66529dbfea6952727e7b"     # 1.1.3  (2022-01-03)
-requires "parsetoml#9cdeb3f65fd10302da157db8a8bac5c42f055249" # 0.6.0  (2021-06-07)
-requires "uuids#8cb8720b567c6bcb261bd1c0f7491bdb5209ad06"     # 0.1.11 (2021-01-15)
+requires "cligen#b962cf8bc0be847cbc1b4f77952775de765e9689"      # 1.5.19 (2021-09-13)
+requires "jsony#2a2cc4331720b7695c8b66529dbfea6952727e7b"       # 1.1.3  (2022-01-03)
+requires "parsetoml#9cdeb3f65fd10302da157db8a8bac5c42f055249"   # 0.6.0  (2021-06-07)
+requires "supersnappy#e4df8cb5468dd96fc5a4764028e20c8a3942f16a" # 2.1.3  (2022-06-12)
+requires "uuids#8cb8720b567c6bcb261bd1c0f7491bdb5209ad06"       # 0.1.11 (2021-01-15)
 # To make Nimble use the pinned `isaac` version, we must pin `isaac` after `uuids`
 # (which has `isaac` as a dependency).
 # Nimble still clones the latest `isaac` tag if there is no tag-versioned one
 # on-disk (e.g. at ~/.nimble/pkgs/isaac-0.1.3), and adds it to the path when
 # building, but (due to writing it later) the pinned version takes precedence.
 # Nimble will support lock files in the future, which should provide more robust
 # version pinning.
-requires "isaac#45a5cbbd54ff59ba3ed94242620c818b9aad1b5b"     # 0.1.3  (2017-11-16)
+requires "isaac#45a5cbbd54ff59ba3ed94242620c818b9aad1b5b"       # 0.1.3  (2017-11-16)
 
 task test, "Runs the test suite":
   exec "nim r ./tests/all_tests.nim"

src/cli.nim

@@ -1,5 +1,5 @@
 import std/[os, parseutils, strformat, strutils, terminal]
-import pkg/cligen/parseopt3
+import pkg/[cligen/parseopt3, supersnappy]
 
 type
   ActionKind* = enum
@@ -295,9 +295,9 @@ func genHelpText: string =
   setLen(result, result.len - 1)
 
 proc showHelp(exitCode: range[0..255] = 0) =
-  const helpText = genHelpText()
+  const helpText = genHelpText().compress()
   let f = if exitCode == 0: stdout else: stderr
-  f.writeLine helpText
+  f.writeLine helpText.uncompress()
   if f == stdout:
     f.flushFile()
   quit(exitCode)
@@ -415,8 +415,8 @@ proc parseOption(kind: CmdLineKind, key: string, val: string): Opt =
         user's cache directory - there is no longer an option to configure the location.
         Performing an offline sync now requires only one option (--offline), but you
         must first run a `configlet sync` command without --offline at least once on
-        your machine.""".unindent()
-      stderr.writeLine msg
+        your machine.""".unindent().compress()
+      stderr.writeLine msg.uncompress()
     showError(&"invalid option: {formatOpt(kind, key)}")
 
 proc parseVal[T: enum](kind: CmdLineKind, key: string, val: string): T =

src/completion/completion.nim

@@ -1,12 +1,13 @@
 import std/[os, strformat]
+import pkg/supersnappy
 import ../cli
 
 proc readCompletions: array[Shell, string] =
   const repoRootDir = currentSourcePath().parentDir().parentDir().parentDir()
   const completionsDir = repoRootDir / "completions"
   for shell in sBash .. result.high:
-    result[shell] = staticRead(completionsDir / &"configlet.{shell}")
+    result[shell] = staticRead(completionsDir / &"configlet.{shell}").compress()
 
 proc completion*(shellKind: Shell) =
   const completions = readCompletions()
-  stdout.write completions[shellKind]
+  stdout.write completions[shellKind].uncompress()