Add nimble clean command

Closes nim-lang#555

src/nimble.nim

@@ -231,6 +231,28 @@ proc buildFromDir(pkgInfo: PackageInfo, paths: HashSet[string],
   cd pkgDir: # Make sure `execHook` executes the correct .nimble file.
     discard execHook(options, actionBuild, false)
 
+proc cleanFromDir(pkgInfo: PackageInfo, options: Options) =
+  ## Clean up build files.
+  # Handle pre-`clean` hook.
+  let pkgDir = pkgInfo.myPath.parentDir()
+
+  cd pkgDir: # Make sure `execHook` executes the correct .nimble file.
+    if not execHook(options, actionClean, true):
+      raise nimbleError("Pre-hook prevented further execution.")
+
+  if pkgInfo.bin.len == 0:
+    return
+
+  for bin, _ in pkgInfo.bin:
+    let outputDir = pkgInfo.getOutputDir("")
+    if dirExists(outputDir):
+      if fileExists(outputDir / bin):
+        removeFile(outputDir / bin)
+
+  # Handle post-`clean` hook.
+  cd pkgDir: # Make sure `execHook` executes the correct .nimble file.
+    discard execHook(options, actionClean, false)
+
 proc promptRemoveEntirePackageDir(pkgDir: string, options: Options) =
   let exceptionMsg = getCurrentExceptionMsg()
   let warningMsgEnd = if exceptionMsg.len > 0: &": {exceptionMsg}" else: "."
@@ -689,6 +711,12 @@ proc build(options: Options) =
   var args = options.getCompilationFlags()
   buildFromDir(pkgInfo, paths, args, options)
 
+proc clean(options: Options) =
+  let dir = getCurrentDir()
+  let pkgInfo = getPkgInfo(dir, options)
+  nimScriptHint(pkgInfo)
+  cleanFromDir(pkgInfo, options)
+
 proc execBackend(pkgInfo: PackageInfo, options: Options) =
   let
     bin = options.getCompilationBinary(pkgInfo).get("")
@@ -1862,6 +1890,8 @@ proc doAction(options: var Options) =
     listPaths(options)
   of actionBuild:
     build(options)
+  of actionClean:
+    clean(options)
   of actionRun:
     run(options)
   of actionCompile, actionDoc:

src/nimblepkg/options.nim

@@ -48,7 +48,8 @@ type
     actionNil, actionRefresh, actionInit, actionDump, actionPublish,
     actionInstall, actionSearch, actionList, actionBuild, actionPath,
     actionUninstall, actionCompile, actionDoc, actionCustom, actionTasks,
-    actionDevelop, actionCheck, actionLock, actionRun, actionSync, actionSetup
+    actionDevelop, actionCheck, actionLock, actionRun, actionSync, actionSetup,
+    actionClean
 
   DevelopActionType* = enum
     datAdd, datRemoveByPath, datRemoveByName, datInclude, datExclude
@@ -58,7 +59,7 @@ type
   Action* = object
     case typ*: ActionType
     of actionNil, actionList, actionPublish, actionTasks, actionCheck,
-       actionLock, actionSetup: nil
+       actionLock, actionSetup, actionClean: nil
     of actionSync:
       listOnly*: bool
     of actionRefresh:
@@ -143,6 +144,7 @@ Commands:
                [-i, --inclDeps]   Uninstalls package and dependent package(s).
   build        [opts, ...] [bin]  Builds a package. Passes options to the Nim
                                   compiler.
+  clean	                          Clean build artifacts.
   run          [opts, ...] [bin]  Builds and runs a package.
                                   Binary needs to be specified after any
                                   compilation options if there are several
@@ -231,6 +233,8 @@ proc parseActionType*(action: string): ActionType =
     result = actionPath
   of "build":
     result = actionBuild
+  of "clean":
+    result = actionClean
   of "run":
     result = actionRun
   of "c", "compile", "js", "cpp", "cc":