Fix pydot regression

CHANGELOG.md

@@ -1,5 +1,19 @@
 # Change Log
 
+## [2.37.1](https://github.com/nerdvegas/rez/tree/2.37.1) (2019-07-19)
+[Full Changelog](https://github.com/nerdvegas/rez/compare/2.37.0...2.37.1)
+
+**Notes**
+
+This fixes a regression introduced in `2.34.0`, which causes `rez-context -g` to
+fail. The pydot vendor package was updated, and the newer version includes a
+breaking change. Where `pydot.graph_from_dot_data` used to return a single graph
+object, it now returns a list of graph objects.
+
+**Merged pull requests:**
+
+- Fix pydot regression [\#XXX](https://github.com/nerdvegas/rez/pull/XXX) ([nerdvegas](https://github.com/nerdvegas))
+
 ## [2.37.0](https://github.com/nerdvegas/rez/tree/2.37.0) (2019-07-19)
 [Full Changelog](https://github.com/nerdvegas/rez/compare/2.36.2...2.37.0)
 

CONTRIBUTING.md

@@ -39,7 +39,8 @@ Here is an example changelog entry:
 
 **Notes**
 
-Fixed error in foo rex command on Windows.
+Describe the fixes the PR addresses here. It's ok if this is a summary of a longer
+description found in the PR itself, in fact that should be common.
 
 **Backwards Compatibility Issues**
 
@@ -49,11 +50,11 @@ reason.
 
 **Merged pull requests:**
 
-- Fix foo command [\#101](https://github.com/nerdvegas/rez/pull/101) ([jbloggs](https://github.com/jbloggs))
+- PR_TITLE_HERE [\#XXX](https://github.com/nerdvegas/rez/pull/XXX) ([USER](https://github.com/USER))
 
 **Closed issues:**
 
-- rex foo command broken [\#102](https://github.com/nerdvegas/rez/issues/102)
+- ISSUE_TITLE_HERE [\#YYY](https://github.com/nerdvegas/rez/issues/YYY)
 ```
 
 Please include the relevant issues that your PR closes, matching the syntax shown above. When the PR is merged to master, the PR info will be added to the same changelog entry by the maintainer. Don't be too concerned with the date and 'full changelog' line, this will also be patched by the maintainer.

src/rez/utils/_version.py

@@ -1,7 +1,7 @@
 
 
 # Update this value to version up Rez. Do not place anything else in this file.
-_rez_version = "2.37.0"
+_rez_version = "2.37.1"
 
 try:
     from rez.vendor.version.version import Version

src/rez/utils/graph_utils.py

@@ -212,15 +212,48 @@ def save_graph(graph_str, dest_file, fmt=None, image_ratio=None):
     Returns:
         String representing format that was written, such as 'png'.
     """
-    g = pydot.graph_from_dot_data(graph_str)
+
+    # Disconnected edges can result in multiple graphs. We should never see
+    # this - it's a bug in graph generation if we do.
+    #
+    graphs = pydot.graph_from_dot_data(graph_str)
+
+    if not graphs:
+        raise RuntimeError("No graph generated")
+
+    if len(graphs) > 1:
+        path, ext = os.path.splitext(dest_file)
+        dest_files = []
+
+        for i, g in enumerate(graphs):
+            try:
+                dest_file_ = "%s.%d%s" % (path, i + 1, ext)
+                save_graph_object(g, dest_file_, fmt, image_ratio)
+                dest_files.append(dest_file_)
+            except:
+                pass
+
+        raise RuntimeError(
+            "More than one graph was generated; this probably indicates a bug "
+            "in graph generation. Graphs were written to %r" % dest_files
+        )
+
+    # write the graph
+    return save_graph_object(graphs[0], dest_file, fmt, image_ratio)
+
+
+def save_graph_object(g, dest_file, fmt=None, image_ratio=None):
+    """Like `save_graph`, but takes a pydot Dot object.
+    """
 
     # determine the dest format
     if fmt is None:
         fmt = os.path.splitext(dest_file)[1].lower().strip('.') or "png"
+
     if hasattr(g, "write_" + fmt):
         write_fn = getattr(g, "write_" + fmt)
     else:
-        raise Exception("Unsupported graph format: '%s'" % fmt)
+        raise RuntimeError("Unsupported graph format: '%s'" % fmt)
 
     if image_ratio:
         g.set_ratio(str(image_ratio))