From 0a48a8e2bed966e58fa1f12a635bcc135786768c Mon Sep 17 00:00:00 2001
From: Artyom <yom@artyom.me>
Date: Sat, 10 Jun 2017 21:06:38 +0200
Subject: [PATCH] Show insertion/deletion places in diffs

---
 src/Guide/Diff.hs  | 8 ++++----
 src/Guide/Views.hs | 8 +++++---
 static/admin.css   | 6 ++++++
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/Guide/Diff.hs b/src/Guide/Diff.hs
index 6f596d0..ef17440 100644
--- a/src/Guide/Diff.hs
+++ b/src/Guide/Diff.hs
@@ -65,8 +65,9 @@ diffR = concatMap hunkToChunk . toList
     hunkToChunk (v, PV.Inserted)  = [Added (tconcat v)]
     hunkToChunk (v, PV.Replaced)  = [Added (tconcat v)]
     hunkToChunk (v, PV.Unchanged) = map Plain (toList v)
-    hunkToChunk (_, PV.Deleted)   = []  -- because it's not present
-                                        -- in the right part
+    -- it's useful to report deleted things as well because then we can mark
+    -- them with tiny rectangles like “insert here”
+    hunkToChunk (_, PV.Deleted)   = [Added ""]
 
 -- | Create a diff for the left (original) part. We only want to highlight
 -- parts which were deleted or replaced.
@@ -83,8 +84,7 @@ diffL = concatMap hunkToChunk
     hunkToChunk (v, PV.Inserted)  = [Deleted (tconcat v)]
     hunkToChunk (v, PV.Replaced)  = [Deleted (tconcat v)]
     hunkToChunk (v, PV.Unchanged) = map Plain (toList v)
-    hunkToChunk (_, PV.Deleted)   = []  -- because it's not present
-                                        -- in the left part
+    hunkToChunk (_, PV.Deleted)   = [Deleted ""]
 
 -- | In a bunch of chunks, find only the part that was changed
 trimDiff
diff --git a/src/Guide/Views.hs b/src/Guide/Views.hs
index e0042ad..c8e5f59 100644
--- a/src/Guide/Views.hs
+++ b/src/Guide/Views.hs
@@ -512,9 +512,11 @@ renderDiff old new =
         mapM_ renderChunk diffRight
         toHtml (mconcat (take 10 diffContextBelow)) >> " [...]"
     --
-    renderChunk (Diff.Added   x) = ins_ (toHtml (showNewlines x))
-    renderChunk (Diff.Deleted x) = del_ (toHtml (showNewlines x))
-    renderChunk (Diff.Plain   x) = toHtml x
+    renderChunk (Diff.Added   "") = ins_ [class_ "empty-chunk"] ""
+    renderChunk (Diff.Added    x) = ins_ (toHtml (showNewlines x))
+    renderChunk (Diff.Deleted "") = del_ [class_ "empty-chunk"] ""
+    renderChunk (Diff.Deleted  x) = del_ (toHtml (showNewlines x))
+    renderChunk (Diff.Plain    x) = toHtml x
     --
     showNewlines x =
       let
diff --git a/static/admin.css b/static/admin.css
index 68f3b32..297c470 100644
--- a/static/admin.css
+++ b/static/admin.css
@@ -77,6 +77,12 @@ textarea:focus {
   white-space: pre-wrap;
 }
 
+#edits .empty-chunk {
+  padding-right: 5px;
+  border: 1px dashed black;
+  border-radius: 4px;
+}
+
 #stats table {
   border-collapse: collapse;
   border-spacing: 0;