Improve context resolve failure info

src/rez/resolved_context.py

@@ -28,7 +28,9 @@
 from rez.shells import create_shell
 from rez.exceptions import ResolvedContextError, PackageCommandError, \
     RezError, _NeverError, PackageCacheError, PackageNotFoundError
-from rez.utils.graph_utils import write_dot, write_compacted, read_graph_from_string
+from rez.utils.graph_utils import write_dot, write_compacted, \
+    read_graph_from_string
+from rez.utils.resolve_graph import failure_detail_from_graph
 from rez.vendor.six import six
 from rez.vendor.version.version import VersionRange
 from rez.vendor.version.requirement import Requirement
@@ -807,13 +809,13 @@ def _rt(t):
                 return time.strftime("%a %b %d %H:%M:%S %Y", time.localtime(t))
 
         if self.status_ in (ResolverStatus.failed, ResolverStatus.aborted):
-            _pr("The context failed to resolve:\n%s"
-                % self.failure_description, critical)
-            return
+            res_status = "resolve failed,"
+        else:
+            res_status = "resolved"
 
         t_str = _rt(self.created)
-        _pr("resolved by %s@%s, on %s, using Rez v%s"
-            % (self.user, self.host, t_str, self.rez_version))
+        _pr("%s by %s@%s, on %s, using Rez v%s"
+            % (res_status, self.user, self.host, t_str, self.rez_version))
         if self.requested_timestamp:
             t_str = _rt(self.requested_timestamp)
             _pr("packages released after %s were ignored" % t_str)
@@ -863,6 +865,21 @@ def _rt(t):
             _pr(line, col)
         _pr()
 
+        # show resolved, or not
+        #
+        if self.status_ in (ResolverStatus.failed, ResolverStatus.aborted):
+            _pr("The context failed to resolve:\n%s"
+                % self.failure_description, critical)
+
+            _pr()
+            _pr(failure_detail_from_graph(self.graph(as_dot=False)))
+            _pr()
+            _pr("To see a graph of the failed resolution, add --fail-graph "
+                "in your rez-env or rez-build command.")
+            _pr()
+
+            return
+
         _pr("resolved packages:", heading)
         rows = []
         colors = []

src/rez/utils/resolve_graph.py

@@ -0,0 +1,129 @@
+
+from rez.utils.graph_utils import _request_from_label
+
+
+def failure_detail_from_graph(graph):
+    """Generate detailed resolve failure messages from graph
+
+    Args:
+        graph (rez.vendor.pygraph.classes.digraph.digraph): context graph object
+
+    """
+    # Base on `rez.solver._ResolvePhase.get_graph()`
+    #   the failure reason has three types:
+    #
+    #   * DependencyConflicts
+    #       which have "conflict" edge in graph
+    #
+    #   * TotalReduction
+    #       which have "conflict" edge and may also have "reduct" edge in graph
+    #
+    #   * Cycle
+    #       which have "cycle" edge in graph
+    #
+    #   so we find cycle edge first, and try other if not found.
+    #
+
+    # find cycle
+    cycled_edge = next((k for k, v in graph.edge_properties.items()
+                        if v["label"] == "CYCLE"), None)
+    if cycled_edge:
+        return _cycled_detail_from_graph(graph, cycled_edge)
+
+    # find conflict
+    conflicted_edge = next((k for k, v in graph.edge_properties.items()
+                            if v["label"] == "CONFLICT"), None)
+    if conflicted_edge:
+        return _conflicted_detail_from_graph(graph, conflicted_edge)
+
+    # should be a healthy graph
+    return ""
+
+
+def _cycled_detail_from_graph(graph, cycled_edge):
+    """Find all initial requests, and walk down till circle back"""
+
+    messages = ["Resolve paths starting from initial requests to cycle:"]
+
+    for init_request in _iter_init_request_nodes(graph):
+        node = init_request
+        visited = list()
+        while True:
+            visited.append(node)
+            down = next((ne for ne in graph.node_neighbors[node]), None)
+            if down in cycled_edge:
+                visited.append(down)
+                break
+            if down is None:
+                break
+
+            node = down
+
+        line = "  %s" % _get_node_label(graph, visited[0])  # init request
+        for node in visited[1:]:
+            # should be more readable if opt-out requests
+            if not _is_request_node(graph, node):
+                line += " --> %s" % _get_node_label(graph, node)
+
+        messages.append(line)
+
+    return "\n".join(messages)
+
+
+def _conflicted_detail_from_graph(graph, conflicted_edge):
+    """Find all initial requests, and walk down till in conflicted edge"""
+
+    messages = ["Resolve paths starting from initial requests to conflict:"]
+
+    for init_request in _iter_init_request_nodes(graph):
+        node = init_request
+        visited = list()
+        while True:
+            visited.append(node)
+            down = next((ne for ne in graph.node_neighbors[node]), None)
+            if down is None:
+                break
+
+            node = down
+
+        line = "  %s" % _get_node_label(graph, visited[0])  # init request
+        for node in visited[1:]:
+            # should be more readable if opt-out requests
+            if not _is_request_node(graph, node):
+                line += " --> %s" % _get_node_label(graph, node)
+
+            # show conflicted request at the end
+            if _is_request_node(graph, node) and node in conflicted_edge:
+                line += " --> %s" % _get_node_label(graph, node)
+                break
+
+        messages.append(line)
+
+    return "\n".join(messages)
+
+
+def _iter_init_request_nodes(graph):
+    request_color = "#FFFFAA"  # NOTE: the color code is hardcoded in `solver`
+    for node, attrs in graph.node_attr.items():
+        for at in attrs:
+            if at[0] == "fillcolor" and at[1] == request_color:
+                yield node
+
+
+def _get_node_label(graph, node):
+    label_ = next(at[1] for at in graph.node_attr[node] if at[0] == "label")
+    return _request_from_label(label_)
+
+
+def _is_request_node(graph, node):
+    style = next(at[1] for at in graph.node_attr[node] if at[0] == "style")
+    return "dashed" in style
+
+
+def _print_each_graph_edges(graph):
+    """for debug"""
+    for (from_, to_), properties in graph.edge_properties.items():
+        edge_status = properties["label"]
+        from_name = _get_node_label(graph, from_)
+        to_name = _get_node_label(graph, to_)
+        print("%s -> %s  %s" % (from_name, to_name, edge_status))