fix exception when the buffer is empty

fcore/text-builder/normal-mode-text-builder.sml

@@ -19,20 +19,14 @@ struct
     , acc
     ) =
     let
-      val {rightStrings, rightLines, line = curLine, idx = curIdx, ...} = buffer
+      val
-    in
+        { rightStrings
-      case (rightStrings, rightLines) of
+        , rightLines
-        (shd :: stl, lhd :: ltl) =>
+        , line = curLine
-          let
+        , idx = curIdx
-            (* get relative index of line to start building from *)
+        , textLength
-            val strPos =
+        , ...
-              Utils.getRelativeLineStartFromRightHead (startLine, curLine, lhd)
+        } = buffer
-            (* get absolute idx of line *)
-            val absIdx = curIdx + strPos
-
-            val searchPos = BinSearch.equalOrMore (absIdx, searchList)
-            val searchPos =
-              if searchPos = ~1 then Vector.length searchList else searchPos
 
       val env = Utils.initEnv
         ( 5
@@ -47,6 +41,29 @@ struct
         , startLine
         )
       val {startX, startY, ...} = env
+    in
+      if textLength = 1 then
+        (* empty string, so there is nothing we can draw 
+         * except a cursor at the line start.
+         * An empty string is usually thought of to have a length of 0 
+         * and this is true, but we always have a \n at the end of the buffer
+         * to respect Unix-style file endings, which we always uphold. 
+         * So, for us, an empty string has a length of 1. *)
+        [Utils.makeCursor (startX, startY, env)]
+      else
+        case (rightStrings, rightLines) of
+          (shd :: stl, lhd :: ltl) =>
+            let
+              (* get relative index of line to start building from *)
+              val strPos =
+                Utils.getRelativeLineStartFromRightHead
+                  (startLine, curLine, lhd)
+              (* get absolute idx of line *)
+              val absIdx = curIdx + strPos
+
+              val searchPos = BinSearch.equalOrMore (absIdx, searchList)
+              val searchPos =
+                if searchPos = ~1 then Vector.length searchList else searchPos
             in
               TextBuilderWithHighlight.build
                 ( strPos

shell/shell.sml

@@ -49,10 +49,27 @@ struct
       ()
     end
 
-  fun ioToLineGap (io, acc) =
+  local
+    fun loop (io, acc, lastCharWasNewline) =
       case TextIO.inputLine io of
-      SOME str => ioToLineGap (io, LineGap.append (str, acc))
+        SOME str =>
-    | NONE => LineGap.goToStart acc
+          let
+            val endsWithNewline =
+              String.size str > 0
+              andalso String.sub (str, String.size str - 1) = #"\n"
+          in
+            loop (io, LineGap.append (str, acc), endsWithNewline)
+          end
+      | NONE =>
+          if lastCharWasNewline then
+            LineGap.goToStart acc
+          else
+            let val acc = LineGap.append ("\n", acc)
+            in LineGap.goToStart acc
+            end
+  in
+    fun ioToLineGap (io, acc) = loop (io, acc, false)
+  end
 
   fun main () =
     let