Index: src/document/katedocument.cpp
===================================================================
--- src/document/katedocument.cpp
+++ src/document/katedocument.cpp
@@ -3975,38 +3975,73 @@
 
 }
 
+int firstGoodChar(const Kate::TextLine &line)
+{
+    // Inspired by (aka stolen from) KTextEditor::ViewPrivate::smartNewline()
+    int col = 0;
+    while (line->length() > col &&
+            !(line->at(col).isLetterOrNumber() || line->at(col) == QLatin1Char('_'))
+          ) {
+        ++col;
+    }
+
+    return col;
+}
+
 void KTextEditor::DocumentPrivate::joinLines(uint first, uint last)
 {
 //   if ( first == last ) last += 1;
     editStart();
-    int line(first);
+    const int line(first);
+
+    Kate::TextLine l = kateTextLine(line);
+    if (!l) { // Just for the overanxious
+        return;
+    }
+    // Smart Join Line: Remove everything from next line(s) which may be annoying...
+    QString peskyPrefix = l->string(0, firstGoodChar(l));
+    if (!peskyPrefix.endsWith(QStringLiteral(" "))) {
+    // ...but try to avoid to damage stuff like HTML or Latex tags...
+        peskyPrefix.clear();
+    } else if (peskyPrefix.endsWith(QStringLiteral("} "))) {
+    // ...and make an exception for braces like in THIS codeblock here
+        peskyPrefix.clear();
+    }
+
     while (first < last) {
         // Normalize the whitespace in the joined lines by making sure there's
         // always exactly one space between the joined lines
         // This cannot be done in editUnwrapLine, because we do NOT want this
         // behavior when deleting from the start of a line, just when explicitly
         // calling the join command
-        Kate::TextLine l = kateTextLine(line);
         Kate::TextLine tl = kateTextLine(line + 1);
 
         if (!l || !tl) {
             editEnd();
             return;
         }
 
-        int pos = tl->firstChar();
-        if (pos >= 0) {
-            if (pos != 0) {
-                editRemoveText(line + 1, 0, pos);
-            }
-            if (!(l->length() == 0 || l->at(l->length() - 1).isSpace())) {
-                editInsertText(line + 1, 0, QLatin1String(" "));
-            }
+        const int pos = l->lastChar();
+        if (pos < 0) {
+            // Line contains only space, clear all
+            editRemoveText(line, 0, l->length());
+        } else if (pos == l->length() - 1) {
+            // No trailing space, add one
+            editInsertText(line, l->length(), QStringLiteral(" "));
         } else {
-            // Just remove the whitespace and let Kate handle the rest
-            editRemoveText(line + 1, 0, tl->length());
+            // Remove all but one trailing space
+            editRemoveText(line, pos + 2, l->length());
+        }
+
+        // Remove all from next line which may annoying, or not
+        if (tl->startsWith(peskyPrefix) && true /*TODO Add config option*/) {
+        // No check here for size=0, will catch in editRemoveText()
+            editRemoveText(line + 1, 0, peskyPrefix.size());
         }
 
+        // Remove all leading space from next line
+        editRemoveText(line + 1, 0, tl->firstChar());
+
         editUnWrapLine(line);
         first++;
     }