Add hints for NimbleErrors which help the user fix them.

src/nimble.nim

@@ -998,10 +998,10 @@ proc doAction(options: Options) =
 
     let execResult = execTask(nimbleFile, options.action.command, options)
     if not execResult.success:
-      writeHelp(false)
-
-      raise newException(NimbleError, "Could not find task $1 in $2" %
-                        [options.action.command, nimbleFile])
+      raiseNimbleError(msg = "Could not find task $1 in $2" %
+                             [options.action.command, nimbleFile],
+                       hint = "Run `nimble --help` and/or `nimble tasks` for" &
+                              " a list of possible commands.")
 
     if execResult.command.normalize == "nop":
       display("Warning:", "Using `setCommand 'nop'` is not necessary.", Warning,
@@ -1027,14 +1027,18 @@ proc doAction(options: Options) =
 
 when isMainModule:
   var error = ""
+  var hint = ""
 
   try:
     parseCmdLine().doAction()
   except NimbleError:
-    error = getCurrentExceptionMsg()
+    let err = (ref NimbleError)(getCurrentException())
+    error = err.msg
     when not defined(release):
       let stackTrace = getStackTrace(getCurrentException())
       error = stackTrace & "\n\n" & error
+    if not err.isNil:
+      hint = err.hint
   except NimbleQuit:
     nil
   finally:
@@ -1043,4 +1047,6 @@ when isMainModule:
   if error.len > 0:
     displayTip()
     display("Error:", error, Error, HighPriority)
+    if hint.len > 0:
+      display("Hint:", hint, Warning, HighPriority)
     quit(1)

src/nimblepkg/common.nim

@@ -40,5 +40,10 @@ when not defined(nimscript):
     ## Same as quit(QuitSuccess), but allows cleanup.
     NimbleQuit* = ref object of Exception
 
+  proc raiseNimbleError*(msg: string, hint = "") =
+    var exc = newException(NimbleError, msg)
+    exc.hint = hint
+    raise exc
+
 const
   nimbleVersion* = "0.7.11"

src/nimblepkg/packageparser.nim

@@ -241,6 +241,8 @@ proc getInstalledPkgs*(libsDir: string, options: Options):
   const
     readErrorMsg = "Installed package $1 v$2 is outdated or corrupt."
     validationErrorMsg = readErrorMsg & "\nPackage did not pass validation: $3"
+    hintMsg = "The corrupted package will need to be removed manually. To fix" &
+              " this error message, remove $1."
 
   proc createErrorMsg(tmplt, path, msg: string): string =
     let (name, version) = getNameVersion(path)
@@ -261,14 +263,16 @@ proc getInstalledPkgs*(libsDir: string, options: Options):
         except ValidationError:
           let exc = (ref ValidationError)(getCurrentException())
           exc.msg = createErrorMsg(validationErrorMsg, path, exc.msg)
+          exc.hint = hintMsg % path
           if exc.warnInstalled:
             display("Warning:", exc.msg, Warning, HighPriority)
           else:
             raise exc
         except:
-          let exc = getCurrentException()
           let tmplt = readErrorMsg & "\nMore info: $3"
-          exc.msg = createErrorMsg(tmplt, path, exc.msg)
+          let msg = createErrorMsg(tmplt, path, getCurrentException().msg)
+          var exc = newException(NimbleError, msg)
+          exc.hint = hintMsg % path
           raise exc
 
 proc isNimScript*(nf: string, options: Options): bool =

src/nimblepkg/version.nim

@@ -34,6 +34,7 @@ type
 
   ParseVersionError* = object of ValueError
   NimbleError* = object of Exception
+    hint*: string
 
 proc newVersion*(ver: string): Version = return Version(ver)
 proc newSpecial*(spe: string): Special = return Special(spe)