cfg: Improve the styling of rendered graphs (#888)

Also switch the output format to svg.

python_ta/cfg/visitor.py

@@ -160,7 +160,7 @@ def visit_while(self, node: nodes.While) -> None:
         )
 
         # Handle "body" branch
-        body_block = self._current_cfg.create_block(test_block)
+        body_block = self._current_cfg.create_block(test_block, edge_label="True")
         self._current_block = body_block
         for child in node.body:
             child.accept(self)
@@ -171,7 +171,7 @@ def visit_while(self, node: nodes.While) -> None:
         self._control_boundaries.pop()
 
         # Handle "else" branch
-        else_block = self._current_cfg.create_block(test_block)
+        else_block = self._current_cfg.create_block(test_block, edge_label="False")
         self._current_block = else_block
         for child in node.orelse:
             child.accept(self)

sample_usage/draw_cfg.py

@@ -8,7 +8,8 @@
 from python_ta.cfg import CFGBlock, CFGVisitor, ControlFlowGraph
 
 USAGE = "USAGE: python -m sample_usage.draw_cfg <your-file.py>"
-GRAPH_OPTIONS = {"format": "jpg", "node_attr": {"shape": "box", "fontname": "Courier New"}}
+GRAPH_OPTIONS = {"format": "svg", "node_attr": {"shape": "box", "fontname": "Courier New"}}
+SUBGRAPH_OPTIONS = {"fontname": "Courier New"}
 
 
 def display(cfgs: Dict[nodes.NodeNG, ControlFlowGraph], filename: str, view: bool = True) -> None:
@@ -22,15 +23,15 @@ def display(cfgs: Dict[nodes.NodeNG, ControlFlowGraph], filename: str, view: boo
             continue
         with graph.subgraph(name=f"cluster_{id(node)}") as c:
             visited = set()
-            _visit(cfg.start, c, visited)
+            _visit(cfg.start, c, visited, cfg.end)
             for block in cfg.unreachable_blocks:
-                _visit(block, c, visited)
-            c.attr(label=subgraph_label)
+                _visit(block, c, visited, cfg.end)
+            c.attr(label=subgraph_label, **SUBGRAPH_OPTIONS)
 
     graph.render(filename, view=view)
 
 
-def _visit(block: CFGBlock, graph: graphviz.Digraph, visited: Set[int]) -> None:
+def _visit(block: CFGBlock, graph: graphviz.Digraph, visited: Set[int], end: CFGBlock) -> None:
     node_id = f"{graph.name}_{block.id}"
     if node_id in visited:
         return
@@ -42,6 +43,8 @@ def _visit(block: CFGBlock, graph: graphviz.Digraph, visited: Set[int]) -> None:
     label = label.replace("\n", "\\l")
 
     fill_color = "grey93" if not block.reachable else "white"
+    # Change the fill colour if block is the end of the cfg
+    fill_color = "black" if block == end else fill_color
 
     graph.node(node_id, label=label, fillcolor=fill_color, style="filled")
     visited.add(node_id)
@@ -51,7 +54,7 @@ def _visit(block: CFGBlock, graph: graphviz.Digraph, visited: Set[int]) -> None:
             graph.edge(node_id, f"{graph.name}_{edge.target.id}", str(edge.label))
         else:
             graph.edge(node_id, f"{graph.name}_{edge.target.id}")
-        _visit(edge.target, graph, visited)
+        _visit(edge.target, graph, visited, end)
 
 
 def main(filepath: str) -> None:

tests/test_cfg/test_label_while.py

@@ -0,0 +1,161 @@
+from typing import Set
+
+import astroid
+
+from python_ta.cfg import CFGVisitor, ControlFlowGraph
+
+
+def build_cfg(src: str) -> ControlFlowGraph:
+    """Build a CFG for testing."""
+    mod = astroid.parse(src)
+    t = CFGVisitor()
+    mod.accept(t)
+
+    return t.cfgs[mod]
+
+
+def _extract_labels(cfg: ControlFlowGraph) -> Set[str]:
+    """Return a set of all the labels in this cfg."""
+    labels = {edge.label for edge in cfg.get_edges() if edge.label is not None}
+    return labels
+
+
+def _extract_num_labels(cfg: ControlFlowGraph) -> int:
+    """Return the number of labelled edges in the cfg."""
+    return sum(1 for edge in cfg.get_edges() if edge.label is not None)
+
+
+def test_num_while_labels() -> None:
+    """Test that the expected number of labels is produced in a while loop."""
+    src = """
+    i = 0
+    while i < 10:
+        i += 1
+
+    print('not else')
+    """
+    expected_num_labels = 2
+    assert _extract_num_labels(build_cfg(src)) == expected_num_labels
+
+
+def test_type_while_labels() -> None:
+    """Test that the content of the labels produced in a while loop is correct."""
+    src = """
+    i = 0
+    while i < 10:
+        i += 1
+
+    print('not else')
+    """
+    expected_labels = {"True", "False"}
+    assert _extract_labels(build_cfg(src)) == expected_labels
+
+
+def test_num_while_else_labels() -> None:
+    """Test that the expected number of labels is produced in a while-else loop."""
+    src = """
+    i = 0
+    while i < 10:
+        i += 1
+    else:
+        print('is else')
+
+    print('not else')
+    """
+    expected_num_labels = 2
+    assert _extract_num_labels(build_cfg(src)) == expected_num_labels
+
+
+def test_type_while_else_labels() -> None:
+    """Test that the content of the labels produced in a while-else loop is correct."""
+    src = """
+    i = 0
+    while i < 10:
+        i += 1
+    else:
+        print('is else')
+
+    print('not else')
+    """
+    expected_labels = {"True", "False"}
+    assert _extract_labels(build_cfg(src)) == expected_labels
+
+
+def test_num_complex_while_labels() -> None:
+    """Test that the number of labels in a complex while loop is correct."""
+    src = """
+    i = 0
+    while i < 10:
+        j = 0
+        while j < 5:
+            j += 1
+        i += 1
+
+        if i > 4:
+            print('hi')
+
+    print('not else')
+    """
+    expected_num_labels = 6
+    assert _extract_num_labels(build_cfg(src)) == expected_num_labels
+
+
+def test_type_complex_while_labels() -> None:
+    """Test that the content of the labels produced in a complex while loop is correct."""
+    src = """
+    i = 0
+    while i < 10:
+        j = 0
+        while j < 5:
+            j += 1
+        i += 1
+
+        if i > 4:
+            print('hi')
+
+    print('not else')
+    """
+    expected_labels = {"True", "False"}
+    assert _extract_labels(build_cfg(src)) == expected_labels
+
+
+def test_num_complex_while_else_labels() -> None:
+    """Test that the number of labels in a complex while-else loop is correct."""
+    src = """
+    i = 0
+    while i < 10:
+        j = 0
+        while j < 5:
+            j += 1
+        i += 1
+
+        if i > 4:
+            print('hi')
+    else:
+        print('is else')
+
+    print('not else')
+    """
+    expected_num_labels = 6
+    assert _extract_num_labels(build_cfg(src)) == expected_num_labels
+
+
+def test_type_complex_while_else_labels() -> None:
+    """Test that the content of the labels produced in a complex while-else loop is correct."""
+    src = """
+    i = 0
+    while i < 10:
+        j = 0
+        while j < 5:
+            j += 1
+        i += 1
+
+        if i > 4:
+            print('hi')
+    else:
+        print('is else')
+
+    print('not else')
+    """
+    expected_labels = {"True", "False"}
+    assert _extract_labels(build_cfg(src)) == expected_labels