ParameterAST: Adding .Help (Fixes #305)

Author: James Brundage

Types/ParameterAST/TypeName.txt

@@ -0,0 +1 @@
+System.Management.Automation.Language.ParamBlockAst

Types/ParameterAST/get_Help.ps1

@@ -0,0 +1,21 @@
+$parameter = $this
+$parameterIndex = $parameter.Parent.Parameters.IndexOf($this)
+
+if ($parameterIndex -eq 0) { # For the first parameter
+    $parentExtent = $parameter.Parent.Extent.ToString()
+    # This starts after the first parenthesis. 
+    $afterFirstParens = $parentExtent.IndexOf('(') + 1
+    # and goes until the start of the parameter.
+    $parentExtent.Substring($afterFirstParens, 
+        $parameter.Extent.StartOffset - 
+            $parameter.Parent.Extent.StartOffset - 
+                $afterFirstParens) -replace '^[\s\r\n]+'
+    # (don't forget to trim leading whitespace)
+} else {
+    # for every other parameter it is the content between parameters.
+    $lastParameter   = $parameter.Parent.Parameters[$parameterIndex - 1]                                    
+    $relativeOffset  = $lastParameter.Extent.EndOffset + 1 - $parameter.Parent.Extent.StartOffset
+    $distance        = $parameter.Extent.StartOffset - $lastParameter.Extent.EndOffset - 1
+    # (don't forget to trim leading whitespace and commas)
+    $parameter.Parent.Extent.ToString().Substring($relativeOffset,$distance) -replace '^[\,\s\r\n]+'
+}