trim empty leading lines from the first subslice of a snippet slice

Author: tayloraswift

Sources/MarkdownPluginSwift/Snippets/SnippetParser.SliceBounds.swift

@@ -24,16 +24,48 @@ extension SnippetParser.SliceBounds
     {
         //  We need to do two passes over the source ranges, as indentation is computed across
         //  the entire slice, and not just one subslice.
+        var trimEmptyLines:Bool = true
         let ranges:[Range<Int>] = self.ranges.compactMap
         {
-            let start:Int = $0.lowerBound.utf8Offset
+            var start:Int = $0.lowerBound.utf8Offset
             if  start >= utf8.endIndex
             {
                 //  This could happen if the file ends with a control comment and no
                 //  final newline.
                 return nil
             }
 
+            //  We need to roll forward through any whitespace-only lines. This is difficult
+            //  to do at the syntax level, because we traditionally associate trailing trivia
+            //  with the token that comes after the slice markers. So we do it here.
+            //
+            //  This should only be done for the first range, to preserve the ability to insert
+            //  empty lines between subslices.
+            if  trimEmptyLines
+            {
+                trimming:
+                while true
+                {
+                    for (i, byte):(Int, UInt8) in zip(start..., utf8[start...])
+                    {
+                        switch byte
+                        {
+                        //  '\r', '\t', ' '
+                        case 0x0D, 0x09, 0x20:
+                            continue
+
+                        //  '\n'
+                        case 0x0A:
+                            start = utf8.index(after: i)
+                            continue trimming
+
+                        default:
+                            break trimming
+                        }
+                    }
+                }
+            }
+
             let end:Int = min($0.upperBound.utf8Offset, utf8.endIndex)
             if  end <= start
             {
@@ -42,6 +74,7 @@ extension SnippetParser.SliceBounds
             }
             else
             {
+                trimEmptyLines = false
                 return start ..< end
             }
         }

Sources/MarkdownPluginSwiftTests/Main.Snippets.swift

@@ -88,28 +88,6 @@ extension Main.Snippets:TestBattery
 
                 """)
         }
-        if  let tests:TestGroup = tests / "CollapseWhitespace"
-        {
-            Self.run(tests: tests,
-                snippet:
-                """
-                /// Here’s how to say ‘hi’ to Barbie.
-
-
-
-                print("Hi Barbie!")
-
-                """,
-                caption:
-                """
-                Here’s how to say ‘hi’ to Barbie.
-                """,
-                slices:
-                """
-                print("Hi Barbie!")
-
-                """)
-        }
         if  let tests:TestGroup = tests / "TriviaOnly"
         {
             Self.run(tests: tests,
@@ -135,13 +113,17 @@ extension Main.Snippets:TestBattery
             Self.run(tests: tests,
                 snippet:
                 """
-                /// Here’s how to say ‘hi’ to Barbie.
+                /// Here’s how to say ‘hi’ to Barbie and Skipper.
 
                 // snippet.HI_BARBIE
 
                 // print("Hi Barbie!")
 
+                // snippet.hide
 
+                // snippet.show
+
+                // print("Hi Skipper!")
 
                 // snippet.end
 
@@ -150,11 +132,12 @@ extension Main.Snippets:TestBattery
                 """
                 Here’s how to say ‘hi’ to Barbie.
                 """,
-                slices:
+                slices: // This should preserve the empty line before `Hi Skipper!`.
                 """
-
                 // print("Hi Barbie!")
 
+                // print("Hi Skipper!")
+
                 """)
         }
         if  let tests:TestGroup = tests / "Indented"
@@ -274,6 +257,51 @@ extension Main.Snippets:TestBattery
 
                 """)
         }
+        if  let tests:TestGroup = tests / "AnonymousCollapseWhitespace"
+        {
+            Self.run(tests: tests,
+                snippet:
+                """
+                /// Here’s how to say ‘hi’ to Barbie.
+
+
+
+                print("Hi Barbie!")
+
+                """,
+                caption:
+                """
+                Here’s how to say ‘hi’ to Barbie.
+                """,
+                slices:
+                """
+                print("Hi Barbie!")
+
+                """)
+        }
+        if  let tests:TestGroup = tests / "NominalCollapseWhitespace"
+        {
+            Self.run(tests: tests,
+                snippet:
+                """
+                /// Here’s how to say ‘hi’ to Barbie.
+
+
+                //  snippet.BARBIE
+
+                print("Hi Barbie!")
+
+                """,
+                caption:
+                """
+                Here’s how to say ‘hi’ to Barbie.
+                """,
+                slices:
+                """
+                print("Hi Barbie!")
+
+                """)
+        }
         if  let tests:TestGroup = tests / "Empty"
         {
             Self.run(tests: tests,