COMMON: Make SpanOwner copy assignment make a copy of the owned Span

To move data from one SpanOwner to another, use `moveFrom`.
Thanks @waltervn for pointing out the problem.

1 files changed, 23 insertions, 8 deletions

diff --git a/common/span.h b/common/span.h
index 2930003811..e0b1d139ca 100644
--- a/common/span.h
+++ b/common/span.h
@@ -942,20 +942,21 @@ public:
 		_span.allocateFromSpan(other._span);
 	}
 
-	/**
-	 * Transfers ownership of the Span from the other owner to this owner.
-	 * If this owner already holds another Span, the old Span will be destroyed.
-	 */
 	inline SpanOwner &operator=(SpanOwner &other) {
 		if (this == &other) {
 			return *this;
 		}
 
-		if (_span.data()) {
-			delete[] const_cast<typename RemoveConst<value_type>::type *>(_span.data());
+		delete[] const_cast<typename RemoveConst<value_type>::type *>(_span.data());
+		_span.clear();
+
+		// Allocating memory when copy-assigning from an unallocated owner
+		// will break the new owner by making it appear allocated even though
+		// it doesn't (and shouldn't) contain data
+		if (other) {
+			_span.allocateFromSpan(other._span);
 		}
-		_span = other._span;
-		other.release();
+
 		return *this;
 	}
 
@@ -964,6 +965,20 @@ public:
 	}
 
 	/**
+	 * Transfers ownership of the Span from the other owner to this owner.
+	 */
+	inline SpanOwner &moveFrom(SpanOwner &other) {
+		if (this == &other) {
+			return *this;
+		}
+
+		delete[] const_cast<typename RemoveConst<value_type>::type *>(_span.data());
+		_span = other._span;
+		other.release();
+		return *this;
+	}
+
+	/**
 	 * Releases the memory owned by this SpanOwner to the caller.
 	 */
 	inline pointer release() {