completion: add configlet completion subcommand (#631)

With this commit, running e.g.

    configlet completion --shell fish

will output the fish completion script to stdout. This allows us to
distribute completion scripts to the user without adding them to the
release assets, which avoids cluttering every directory in which the
user runs `fetch-configlet`.

For example, the user can enable completions for fish by running:

    configlet completion -s fish > ~/.config/fish/completions/configlet.fish

Closes: #630

Author: ee7

Diff for: README.md

@@ -11,13 +11,18 @@ Usage:
   configlet [global-options] <command> [command-options]
 
 Commands:
-  fmt       Format the exercise '.meta/config.json' files
-  generate  Generate Concept Exercise 'introduction.md' files from 'introduction.md.tpl' files
-  info      Print some information about the track
-  lint      Check the track configuration for correctness
-  sync      Check or update Practice Exercise docs, metadata, and tests from 'problem-specifications'.
-            Check or populate missing 'files' values for Concept/Practice Exercises from the track 'config.json'.
-  uuid      Output new (version 4) UUIDs, suitable for the value of a 'uuid' key
+  completion  Output a completion script for a given shell
+  fmt         Format the exercise '.meta/config.json' files
+  generate    Generate Concept Exercise 'introduction.md' files from 'introduction.md.tpl' files
+  info        Print some information about the track
+  lint        Check the track configuration for correctness
+  sync        Check or update Practice Exercise docs, metadata, and tests from 'problem-specifications'.
+              Check or populate missing 'files' values for Concept/Practice Exercises from the track 'config.json'.
+  uuid        Output new (version 4) UUIDs, suitable for the value of a 'uuid' key
+
+Options for completion:
+  -s, --shell <shell>          Choose the shell type (required)
+                               Allowed values: b[ash], f[ish]
 
 Options for fmt:
   -e, --exercise <slug>        Only operate on this exercise

Diff for: src/cli.nim

@@ -4,13 +4,19 @@ import pkg/cligen/parseopt3
 type
   ActionKind* = enum
     actNil = "nil"
+    actCompletion = "completion"
     actFmt = "fmt"
     actGenerate = "generate"
     actInfo = "info"
     actLint = "lint"
     actSync = "sync"
     actUuid = "uuid"
 
+  Shell* = enum
+    sNil = "nil"
+    sBash = "bash"
+    sFish = "fish"
+
   SyncKind* = enum
     skDocs = "docs"
     skFilepaths = "filepaths"
@@ -26,6 +32,8 @@ type
     case kind*: ActionKind
     of actNil, actGenerate, actLint:
       discard
+    of actCompletion:
+      shell*: Shell
     of actFmt:
       # We can't name these fields `exercise`, `update`, and `yes` because we
       # use those names in `actSync`, and Nim doesn't yet support duplicate
@@ -62,6 +70,9 @@ type
     optTrackDir = "trackDir"
     optVerbosity = "verbosity"
 
+    # Options for `completion`
+    optCompletionShell = "shell"
+
     # Options for both `fmt` and `sync`
     optFmtSyncExercise = "exercise"
     optFmtSyncUpdate = "update"
@@ -133,8 +144,10 @@ func genHelpText: string =
     ## Returns a string that describes the allowed values for an enum `T`.
     result = "Allowed values: "
     for val in T:
-      result.add &"{($val)[0]}"
-      result.add &"[{($val)[1 .. ^1]}], "
+      let s = $val
+      if s != "nil":
+        result.add s[0]
+        result.add &"[{s[1 .. ^1]}], "
     setLen(result, result.len - 2)
 
   func genSyntaxStrings: tuple[syntax: array[Opt, string], maxLen: int] =
@@ -147,6 +160,7 @@ func genHelpText: string =
         case opt
         of optTrackDir: "dir"
         of optVerbosity: "verbosity"
+        of optCompletionShell: "shell"
         of optFmtSyncExercise: "slug"
         of optSyncTests: "mode"
         of optUuidNum: "int"
@@ -174,6 +188,7 @@ func genHelpText: string =
 
   const actionDescriptions: array[ActionKind, string] = [
     actNil: "",
+    actCompletion: "Output a completion script for a given shell",
     actFmt: "Format the exercise '.meta/config.json' files",
     actGenerate: "Generate Concept Exercise 'introduction.md' files from 'introduction.md.tpl' files",
     actInfo: "Print some information about the track",
@@ -199,6 +214,8 @@ func genHelpText: string =
     optTrackDir: "Specify a track directory to use instead of the current directory",
     optVerbosity: &"The verbosity of output.\n" &
                   &"{paddingOpt}{allowedValues(Verbosity)} (default: normal)",
+    optCompletionShell: &"Choose the shell type (required)\n" &
+                        &"{paddingOpt}{allowedValues(Shell)}",
     optFmtSyncExercise: "Only operate on this exercise",
     optFmtSyncUpdate: "Prompt to update the unsynced track data",
     optFmtSyncYes: &"Auto-confirm prompts from --{$optFmtSyncUpdate} for updating docs, filepaths, and metadata",
@@ -330,7 +347,7 @@ func formatOpt(kind: CmdLineKind, key: string, val = ""): string =
 func init*(T: typedesc[Action], actionKind: ActionKind,
            scope: set[SyncKind] = {}): T =
   case actionKind
-  of actNil, actFmt, actGenerate, actInfo, actLint:
+  of actNil, actCompletion, actFmt, actGenerate, actInfo, actLint:
     T(kind: actionKind)
   of actSync:
     T(kind: actionKind, scope: scope)
@@ -463,6 +480,12 @@ proc handleOption(conf: var Conf; kind: CmdLineKind; key, val: string) =
     case conf.action.kind
     of actNil, actGenerate, actLint:
       discard
+    of actCompletion:
+      case opt
+      of optCompletionShell:
+        setActionOpt(shell, parseVal[Shell](kind, key, val))
+      else:
+        discard
     of actFmt:
       case opt
       of optFmtSyncExercise:
@@ -533,6 +556,9 @@ proc processCmdLine*: Conf =
   case result.action.kind
   of actNil:
     showHelp()
+  of actCompletion:
+    if result.action.shell == sNil:
+      showError("Please choose a shell. For example: `configlet completion -s bash`")
   of actFmt, actGenerate, actInfo, actLint, actUuid:
     discard
   of actSync:

Diff for: src/completion/completion.nim

@@ -0,0 +1,12 @@
+import std/[os, strformat]
+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}")
+
+proc completion*(shellKind: Shell) =
+  const completions = readCompletions()
+  stdout.write completions[shellKind]

Diff for: src/configlet.nim

@@ -1,6 +1,6 @@
 import std/posix
-import "."/[cli, fmt/fmt, info/info, generate/generate, lint/lint, logger,
-            sync/sync, uuid/uuid]
+import "."/[cli, completion/completion, fmt/fmt, info/info, generate/generate,
+            lint/lint, logger, sync/sync, uuid/uuid]
 
 proc main =
   onSignal(SIGTERM):
@@ -13,6 +13,8 @@ proc main =
   case conf.action.kind
   of actNil:
     discard
+  of actCompletion:
+    completion(conf.action.shell)
   of actFmt:
     fmt(conf)
   of actLint:

Diff for: tests/test_binary.nim

@@ -929,6 +929,32 @@ proc testsForGenerate(binaryPath: string) =
     test "and writes the `introduction.md` file as expected":
       checkNoDiff(trackDir)
 
+proc testsForCompletion(binaryPath: string) =
+  suite "completion":
+    const completionsDir = repoRootDir / "completions"
+    for shell in ["bash", "fish"]:
+      test shell:
+        let c = shell[0]
+        # Convert platform-specific line endings (e.g. CR+LF on Windows) to LF
+        # before comparing. The below `replace` makes the tests pass on Windows.
+        let expected = readFile(completionsDir / &"configlet.{shell}").replace("\p", "\n")
+        execAndCheck(0, &"{binaryPath} completion --shell {shell}", expected)
+        execAndCheck(0, &"{binaryPath} completion --shell {c}", expected)
+        execAndCheck(0, &"{binaryPath} completion -s {shell}", expected)
+        execAndCheck(0, &"{binaryPath} completion -s {c}", expected)
+        execAndCheck(0, &"{binaryPath} completion -s{c}", expected)
+    for shell in ["powershell", "zsh"]:
+      test &"{shell} (produces an error)":
+        let (outp, exitCode) = execCmdEx(&"{binaryPath} completion -s {shell}")
+        check:
+          outp.contains(&"invalid value for '-s': '{shell}'")
+          exitCode == 1
+    test "the -s option is required":
+      let (outp, exitCode) = execCmdEx(&"{binaryPath} completion")
+      check:
+        outp.contains(&"Please choose a shell. For example: `configlet completion -s bash`")
+        exitCode == 1
+
 proc main =
   const
     binaryExt =
@@ -1081,5 +1107,7 @@ proc main =
 
   testsForGenerate(binaryPath)
 
+  testsForCompletion(binaryPath)
+
 main()
 {.used.}