Fixes #290.

src/nimble.nim

@@ -650,6 +650,7 @@ proc listPaths(options: Options) =
   ## but at the end quits with a non zero exit error.
   ##
   ## On success the proc returns normally.
+  cli.setSuppressMessages(true)
   assert options.action.typ == actionPath
   assert(not options.action.packages.isNil)
 
@@ -720,6 +721,7 @@ proc getPackageByPattern(pattern: string, options: Options): PackageInfo =
     result = getPkgInfoFromFile(skeletonInfo.myPath, options)
 
 proc dump(options: Options) =
+  cli.setSuppressMessages(true)
   let p = getPackageByPattern(options.action.projName, options)
   echo "name: ", p.name.escape
   echo "version: ", p.version.escape

src/nimblepkg/cli.nim

@@ -20,6 +20,10 @@ type
     warnings: HashSet[(string, string)]
     suppressionCount: int ## Amount of messages which were not shown.
     showColor: bool ## Whether messages should be colored.
+    suppressMessages: bool ## Whether Warning, Message and Success messages
+                           ## should be suppressed, useful for
+                           ## commands like `dump` whose output should be
+                           ## machine readable.
 
   Priority* = enum
     DebugPriority, LowPriority, MediumPriority, HighPriority
@@ -42,7 +46,8 @@ proc newCLI(): CLI =
     level: HighPriority,
     warnings: initSet[(string, string)](),
     suppressionCount: 0,
-    showColor: true
+    showColor: true,
+    suppressMessages: false
   )
 
 var globalCLI = newCLI()
@@ -77,6 +82,13 @@ proc displayLine(category, line: string, displayType: DisplayType,
 
 proc display*(category, msg: string, displayType = Message,
               priority = MediumPriority) =
+
+  # Don't print any Warning, Message or Success messages when suppression of
+  # warnings is enabled. That is, unless the user asked for --verbose output.
+  if globalCLI.suppressMessages and displayType >= Warning and
+     globalCLI.level == HighPriority:
+    return
+
   # Multiple warnings containing the same messages should not be shown.
   let warningPair = (category, msg)
   if displayType == Warning:
@@ -155,6 +167,9 @@ proc setVerbosity*(level: Priority) =
 proc setShowColor*(val: bool) =
   globalCLI.showColor = val
 
+proc setSuppressMessages*(val: bool) =
+  globalCLI.suppressMessages = val
+
 when isMainModule:
   display("Reading", "config file at /Users/dom/.config/nimble/nimble.ini",
           priority = LowPriority)