logarithmically smaller diff patches when changing expression trees

src/org/rascalmpl/library/analysis/diff/edits/HiFiTreeDiff.rsc

@@ -226,6 +226,94 @@ list[TextEdit] treeDiff(
     = [replace(t@\loc, learnIndentation(t@\loc, "<r>", "<t>"))]
     when t != r;
 
+// Several ways of changing recursive expressions can be exploited to create very small diffs.
+// This is comparable to finding large common sublists in the case of lists. If you look at 
+// unary and binary associative operators as a kind of operator-separated lists, this makes sense.
+
+// remove a unary prefix operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [lit(_), _, sort(exp)], _), [Tree op, _, Tree r]), 
+    r)
+    = [delete(fromUntil(op@\loc, r@\loc))];
+
+// add a unary prefix operator
+list[TextEdit] treeDiff(
+    Tree r,
+    appl(prod(sort(str exp), [lit(_), _, sort(exp)], _), [Tree op, Tree sp, r]))
+    = [replace(beginOf(r@\loc), "<op><sp>")];
+
+// remove a unary postfix operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [sort(str exp), _, lit(_)], _), [Tree l, _, Tree r]), 
+    r)
+    = [delete(cover([endOf(l@\loc), r@\loc]))];
+
+// add a unary postfix operator
+list[TextEdit] treeDiff(
+    Tree l,
+    appl(prod(sort(str exp), [sort(str exp), _, lit(_)], _), [l, Tree sp, Tree op]))
+    = [replace(endOf(l), "<sp><op>")];
+
+// remove the left hand side of a binary operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [sort(exp), _, lit(_), _, sort(exp)], _), [Tree l, _, _, _, Tree r]), 
+    r)
+    = [delete(fromUntil(l@\loc, r@\loc))];
+
+// add the left hand side of a binary operator
+list[TextEdit] treeDiff(
+    Tree r,
+    appl(prod(sort(str exp), [sort(exp), _, lit(_), _, sort(exp)], _), [Tree l, Tree sp1, Tree op, Tree sp2, r]))
+    = [replace(beginOf(r@\loc), "<l><sp1><op><sp2>")];
+
+// remove the right hand side of a binary operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [sort(exp), _, lit(_), _, sort(exp)], _), [Tree l, _, _, _, Tree r]), 
+    l)
+    = [delete(cover([endOf(l@\loc), r@\loc]))];
+
+// add the right hand side of a binary operator
+list[TextEdit] treeDiff(
+    Tree l,
+    appl(prod(sort(str exp), [sort(exp), _, lit(_), _, sort(exp)], _), [l, Tree sp1, Tree op, Tree sp2, Tree r]))
+    = [replace(endOf(l@\loc), "<sp1><op><sp2><r>")];
+
+// change a binary operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [sort(exp), _, lit(str x), _, sort(exp)], _), [Tree l, _, Tree op, _, Tree r]), 
+    appl(prod(sort(str exp), [sort(exp), _, lit(str y), _, sort(exp)], _), [l, _, Tree newOp, _, r]))
+    = [replace(op@\loc, "<newOp>")] when x != y;
+
+// change a prefix operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [lit(str x), _, sort(exp)], _), [Tree op, _, Tree r]), 
+    appl(prod(sort(str exp), [lit(str y), _, sort(exp)], _), [Tree newOp, _, r]))
+    = [replace(op@\loc, "<newOp>")] when x != y;
+
+// change a postfix operator
+list[TextEdit] treeDiff(
+    appl(prod(sort(str exp), [sort(exp), _, lit(str x)], _), [Tree l, _, Tree op]), 
+    appl(prod(sort(str exp), [sort(exp), _, lit(str y)], _), [l, _, Tree newOp]))
+    = [replace(op@\loc, "<newOp>")] when x != y;
+
+// remove brackets
+list[TextEdit] treeDiff(
+    t:appl(prod(sort(str exp), [lit(_), _, sort(exp), _, lit(_)], {*_, \bracket()}), [_, _, Tree e, _, _]), 
+    e)
+    = [
+        delete(fromUntil(beginOf(t@\loc), e@\loc)),
+        delete(fromUntil(endOf(e@\loc), endOf(t@\loc)))
+    ];
+
+// add brackets
+list[TextEdit] treeDiff(
+    Tree e,
+    t:appl(prod(sort(str exp), [lit(_), _, sort(exp), _, lit(_)], {*_, \bracket()}), [Tree open, Tree sp1, Tree e, Tree sp2, Tree close]))
+    = [
+        replace(beginOf(e@\loc), "<open><sp1>"),
+        replace(endOf(e@\loc), "<sp2><close>")
+    ];
+
 // When the productions are different, we've found an edit, and there is no need to recurse deeper.
 default list[TextEdit] treeDiff(
     t:appl(Production p:prod(_,_,_), list[Tree] _), 
@@ -383,6 +471,9 @@ up to `until`.
 private loc fromUntil(loc from, loc until) = from.top(from.offset, until.offset - from.offset);
 private int end(loc src) = src.offset + src.length;
 
+private loc endOf(loc src) = src.top[offset=src.offset + src.length][length=0];
+private loc beginOf(loc src) = src.top[offset=src.offset][length=0];
+
 private loc after(loc src) = src(end(src), 0);
 
 private loc endCover(loc span, []) = span(span.offset + span.length, 0);