[librsvg] (#506): Fix empty patterns which reference a fallback pattern with children

[Federico Mena Quintero <federico src gnome org>]

commit ae7ecfa0846b40d75f5b20c4f122df9a0b78ee4f
Author: Federico Mena Quintero <federico gnome org>
Date:   Thu Sep 19 15:25:03 2019 -0500

    (#506): Fix empty patterns which reference a fallback pattern with children
    
    When we do draw_ctx.acquired_nodes().get_node_of_type() to acquire a
    pattern, or its fallback, we need to set the NodePattern.node to the
    corresponding node weakref.
    
    This was being done correctly at the beginning of the implementation
    of resolve(), as of commit 03cbbe96, where the sequence is this:
    
        DrawingCtx.set_source_paint_server()
            paint_server = acquired_nodes.get_node()
            <paint_server as NodePattern>.resolve_fallbacks_and_set_pattern()
                self.resolve(node, ...)
                    *self.node.borrow_mut() = Some(node.downgrade());
    
    However, this setting of self.node (where self is a NodePattern) to
    the corresponding weakref was missing in the "while" loop in
    NodePattern.resolve(), where it acquires the fallback pattern - the
    fallback's NodePattern also needs its .node to be set to its node's
    weakref.
    
    We'll clean this up at some point.
    
    Fixes https://gitlab.gnome.org/GNOME/librsvg/issues/506

 rsvg_internals/src/pattern.rs                        |   6 +++++-
 .../reftests/bugs/506-pattern-fallback-ref.png       | Bin 0 -> 486 bytes
 .../fixtures/reftests/bugs/506-pattern-fallback.svg  |  19 +++++++++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)
---
diff --git a/rsvg_internals/src/pattern.rs b/rsvg_internals/src/pattern.rs
index 9d943b1d..291d81d3 100644
--- a/rsvg_internals/src/pattern.rs
+++ b/rsvg_internals/src/pattern.rs
@@ -164,7 +164,11 @@ impl PaintSource for NodePattern {
                 }
 
                 let node_data = a_node.borrow();
-                result.resolve_from_fallback(&node_data.get_impl::<NodePattern>());
+
+                let fallback_pattern = node_data.get_impl::<NodePattern>();
+                *fallback_pattern.node.borrow_mut() = Some(a_node.downgrade());
+
+                result.resolve_from_fallback(fallback_pattern);
 
                 stack.push(a_node);
             } else {
diff --git a/tests/fixtures/reftests/bugs/506-pattern-fallback-ref.png 
b/tests/fixtures/reftests/bugs/506-pattern-fallback-ref.png
new file mode 100644
index 00000000..b9fec4e9
Binary files /dev/null and b/tests/fixtures/reftests/bugs/506-pattern-fallback-ref.png differ
diff --git a/tests/fixtures/reftests/bugs/506-pattern-fallback.svg 
b/tests/fixtures/reftests/bugs/506-pattern-fallback.svg
new file mode 100644
index 00000000..64f71050
--- /dev/null
+++ b/tests/fixtures/reftests/bugs/506-pattern-fallback.svg
@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg xmlns="http://www.w3.org/2000/svg";
+     xmlns:xlink="http://www.w3.org/1999/xlink";
+     version="1.1"
+     width="256"
+     height="256"
+     viewBox="0 0 256 256">
+  <defs>
+    <pattern id="pattern1" xlink:href="#pattern2"/>
+    <pattern id="pattern2" patternUnits="userSpaceOnUse" width="1" height="1">
+      <image width="1" height="1" preserveAspectRatio="none"
+             
xlink:href="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVQI12Ng+M8AAAICAQCqKp4n
+AAAAAElFTkSuQmCC"
+             x="0"
+             y="0"/>
+    </pattern>
+  </defs>
+  <rect x="100" y="100" width="56" height="56" style="fill:url(#pattern1);"/>
+</svg>