Feature: Add --probSpecsDir option

The user can now tell the program to use an existing
`problem-specifications` directory, in which case it doesn't make a
temporary shallow clone.

This saves a significant amount of time, and is probably the biggest
possible speed optimisation given that the program running time in
non-interactive mode is essentially the time it takes to establish an
up-to-date `problem-specifications` directory. But perhaps we could
consider adding an "offline-mode" in the future.

This commit also makes it easier to add tests.

Decisions:
- Show an error if the given `problem-specifications` working directory
  is not clean, rather than asking the user or stashing changes.

Closes: exercism#47

src/cli.nim

@@ -16,9 +16,11 @@ type
     exercise*: Option[string]
     mode*: Mode
     verbosity*: Verbosity
+    probSpecsDir*: Option[string]
 
   Opt = enum
-    optExercise, optCheck, optMode, optVerbosity, optHelp, optVersion
+    optExercise, optCheck, optMode, optVerbosity, optProbSpecsDir,
+    optHelp, optVersion
 
   OptKey = tuple
     short: string
@@ -32,6 +34,7 @@ const
     ("c", "check"),
     ("m", "mode"),
     ("o", "verbosity"),
+    ("p", "probSpecsDir"),
     ("h", "help"),
     ("v", "version"),
   ]
@@ -54,6 +57,7 @@ Options:
   -{optCheck.short}, --{optCheck.long}                  Check if there are missing tests. Doesn't update the tests. Terminates with a non-zero exit code if one or more tests are missing
   -{optMode.short}, --{optMode.long} <mode>            What to do with missing test cases. Allowed values: c[hoose], i[nclude], e[xclude]
   -{optVerbosity.short}, --{optVerbosity.long} <verbosity>  The verbosity of output. Allowed values: q[uiet], n[ormal], d[etailed]
+  -{optProbSpecsDir.short}, --{optProbSpecsDir.long} <dir>     Use this `problem-specifications` directory, rather than cloning temporarily
   -{optHelp.short}, --{optHelp.long}                   Show this help message and exit
   -{optVersion.short}, --{optVersion.long}                Show this tool's version information and exit"""
 
@@ -63,7 +67,7 @@ proc showVersion =
   echo &"Canonical Data Syncer v{NimblePkgVersion}"
   quit(0)
 
-proc showError(s: string) =
+proc showError*(s: string) =
   stdout.styledWrite(fgRed, "Error: ")
   stdout.write(s)
   stdout.write("\n\n")
@@ -134,6 +138,9 @@ proc processCmdLine*: Conf =
       of optVerbosity.short, optVerbosity.long:
         showErrorForMissingVal(kind, key, val)
         result.verbosity = parseVerbosity(kind, key, val)
+      of optProbSpecsDir.short, optProbSpecsDir.long:
+        showErrorForMissingVal(kind, key, val)
+        result.probSpecsDir = some(val)
       of optHelp.short, optHelp.long:
         showHelp()
       of optVersion.short, optVersion.long:

src/probspecs.nim

@@ -102,12 +102,47 @@ proc findProbSpecsExercises(repo: ProbSpecsRepo, conf: Conf): seq[ProbSpecsExerc
     if conf.exercise.isNone or conf.exercise.get() == repoExercise.slug:
       result.add(initProbSpecsExercise(repoExercise))
 
-proc findProbSpecsExercises*(conf: Conf): seq[ProbSpecsExercise] =
-  let probSpecsRepo = initProbSpecsRepo()
-
+template withDir(dir: string; body: untyped): untyped =
+  ## Changes the current directory to `dir` temporarily.
+  let startDir = getCurrentDir()
   try:
-    probSpecsRepo.remove()
-    probSpecsRepo.clone()
-    probSpecsRepo.findProbSpecsExercises(conf)
+    setCurrentDir(dir)
+    body
   finally:
-    probSpecsRepo.remove()
+    setCurrentDir(startDir)
+
+proc findProbSpecsExercises*(conf: Conf): seq[ProbSpecsExercise] =
+  const mainBranchName = "master"
+
+  if conf.probSpecsDir.isSome():
+    let probSpecsDir = conf.probSpecsDir.get()
+    logDetailed(&"Using user-provided problem-specifications dir: {probSpecsDir}")
+    if not dirExists(probSpecsDir):
+      showError(&"the given problem-specifications directory does not exist: '{probSpecsDir}'")
+    withDir probSpecsDir:
+      if execCmd("git rev-parse") != 0:
+        showError(&"the given problem-specifications directory is not a git repository: '{probSpecsDir}'")
+
+      if execCmd("git diff-index --quiet HEAD") != 0: # Ignores untracked files.
+        echo &"\nUnstaged changes in {probSpecsDir}:"
+        discard execCmd("git status --short --untracked=no")
+        showError(&"the given problem-specifications working directory is not clean: '{probSpecsDir}'")
+
+      if execCmd(&"git checkout --quiet {mainBranchName}") != 0:
+        showError(&"failed to checkout `{mainBranchName}` in problem-specifications directory: '{probSpecsDir}'")
+
+      if execCmd("git fetch --quiet") != 0: # Separate `fetch` and `merge`.
+        showError(&"failed to fetch `{mainBranchName}` in problem-specifications directory: '{probSpecsDir}'")
+
+      if execCmd("git merge --quiet --ff-only") != 0:
+        showError(&"failed to merge upstream changes in problem-specifications directory: '{probSpecsDir}'")
+
+    result = ProbSpecsRepo(dir: probSpecsDir).findProbSpecsExercises(conf)
+  else:
+    let probSpecsRepo = initProbSpecsRepo()
+    try:
+      probSpecsRepo.remove()
+      probSpecsRepo.clone()
+      result = probSpecsRepo.findProbSpecsExercises(conf)
+    finally:
+      probSpecsRepo.remove()