fix: better understanding of constant conditions

nedbat · Feb 15, 2025 · 0eb3222 · 0eb3222
1 parent 1bf0db2
commit 0eb3222
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Showing 13 changed files with 147 additions and 121 deletions.
diff --git a/CHANGES.rst b/CHANGES.rst
@@ -23,7 +23,10 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- Many constant tests in if statements are now recognized as being optimized
+  away.  For example, previously ``if 13:`` would have been considered a branch
+  with one path not taken.  Now it is understood as always true and no coverage
+  is missing.
 
 
 .. start-releases

diff --git a/coverage/parser.py b/coverage/parser.py
@@ -654,23 +654,28 @@ def __init__(self, body: Sequence[ast.AST]) -> None:
 # TODO: Shouldn't the cause messages join with "and" instead of "or"?
 
 
-def is_constant_test_expr(node: ast.AST) -> bool:
+def is_constant_test_expr(node: ast.AST) -> tuple[bool, bool]:
     """Is this a compile-time constant test expression?
 
     We don't try to mimic all of CPython's optimizations.  We just have to
     handle the kinds of constant expressions people might actually use.
 
     """
     if isinstance(node, ast.Constant):
-        return True
+        return True, bool(node.value)
     elif isinstance(node, ast.Name):
         if node.id in ["True", "False", "None", "__debug__"]:
-            return True
+            return True, eval(node.id)
     elif isinstance(node, ast.UnaryOp) and isinstance(node.op, ast.Not):
-        return is_constant_test_expr(node.operand)
+        is_constant, val = is_constant_test_expr(node.operand)
+        return is_constant, not val
     elif isinstance(node, ast.BoolOp):
-        return all(is_constant_test_expr(v) for v in node.values)
-    return False
+        rets = [is_constant_test_expr(v) for v in node.values]
+        is_constant = all(is_const for is_const, _ in rets)
+        if is_constant:
+            op = any if isinstance(node.op, ast.Or) else all
+            return True, op(v for _, v in rets)
+    return False, False
 
 
 class AstArcAnalyzer:
@@ -1156,10 +1161,14 @@ def _handle__For(self, node: ast.For) -> set[ArcStart]:
 
     def _handle__If(self, node: ast.If) -> set[ArcStart]:
         start = self.line_for_node(node.test)
-        from_start = ArcStart(start, cause="the condition on line {lineno} was never true")
-        exits = self.process_body(node.body, from_start=from_start)
-        from_start = ArcStart(start, cause="the condition on line {lineno} was always true")
-        exits |= self.process_body(node.orelse, from_start=from_start)
+        constant_test, val = is_constant_test_expr(node.test)
+        exits = set()
+        if not constant_test or val:
+            from_start = ArcStart(start, cause="the condition on line {lineno} was never true")
+            exits |= self.process_body(node.body, from_start=from_start)
+        if not constant_test or not val:
+            from_start = ArcStart(start, cause="the condition on line {lineno} was always true")
+            exits |= self.process_body(node.orelse, from_start=from_start)
         return exits
 
     if sys.version_info >= (3, 10):
@@ -1271,7 +1280,7 @@ def _handle__Try(self, node: ast.Try) -> set[ArcStart]:
 
     def _handle__While(self, node: ast.While) -> set[ArcStart]:
         start = to_top = self.line_for_node(node.test)
-        constant_test = is_constant_test_expr(node.test)
+        constant_test, _ = is_constant_test_expr(node.test)
         top_is_body0 = False
         if constant_test:
             top_is_body0 = True

diff --git a/tests/gold/html/partial/class_index.html b/tests/gold/html/partial/class_index.html
@@ -4,8 +4,8 @@
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
     <title>Coverage report</title>
     <link rel="icon" sizes="32x32" href="favicon_32_cb_58284776.png">
-    <link rel="stylesheet" href="style_cb_718ce007.css" type="text/css">
-    <script src="coverage_html_cb_d1c4fcc4.js" defer></script>
+    <link rel="stylesheet" href="style_cb_8e611ae1.css" type="text/css">
+    <script src="coverage_html_cb_6fb7b396.js" defer></script>
 </head>
 <body class="indexfile">
 <header>
@@ -56,8 +56,8 @@ <h2>
                 <a class="button current">Classes</a>
         </h2>
         <p class="text">
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.1a0.dev1">coverage.py v7.5.1a0.dev1</a>,
-            created at 2024-04-29 17:40 -0300
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
 </header>
@@ -107,8 +107,8 @@ <h2>
 <footer>
     <div class="content">
         <p>
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.1a0.dev1">coverage.py v7.5.1a0.dev1</a>,
-            created at 2024-04-29 17:40 -0300
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
     <aside class="hidden">

diff --git a/tests/gold/html/partial/function_index.html b/tests/gold/html/partial/function_index.html
@@ -4,8 +4,8 @@
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
     <title>Coverage report</title>
     <link rel="icon" sizes="32x32" href="favicon_32_cb_58284776.png">
-    <link rel="stylesheet" href="style_cb_718ce007.css" type="text/css">
-    <script src="coverage_html_cb_d1c4fcc4.js" defer></script>
+    <link rel="stylesheet" href="style_cb_8e611ae1.css" type="text/css">
+    <script src="coverage_html_cb_6fb7b396.js" defer></script>
 </head>
 <body class="indexfile">
 <header>
@@ -56,8 +56,8 @@ <h2>
                 <a class="button" href="class_index.html">Classes</a>
         </h2>
         <p class="text">
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.1a0.dev1">coverage.py v7.5.1a0.dev1</a>,
-            created at 2024-04-29 17:40 -0300
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
 </header>
@@ -107,8 +107,8 @@ <h2>
 <footer>
     <div class="content">
         <p>
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.1a0.dev1">coverage.py v7.5.1a0.dev1</a>,
-            created at 2024-04-29 17:40 -0300
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
     <aside class="hidden">

diff --git a/tests/gold/html/partial/index.html b/tests/gold/html/partial/index.html
@@ -4,8 +4,8 @@
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
     <title>Coverage report</title>
     <link rel="icon" sizes="32x32" href="favicon_32_cb_58284776.png">
-    <link rel="stylesheet" href="style_cb_718ce007.css" type="text/css">
-    <script src="coverage_html_cb_d1c4fcc4.js" defer></script>
+    <link rel="stylesheet" href="style_cb_8e611ae1.css" type="text/css">
+    <script src="coverage_html_cb_6fb7b396.js" defer></script>
 </head>
 <body class="indexfile">
 <header>
@@ -55,8 +55,8 @@ <h2>
                 <a class="button" href="class_index.html">Classes</a>
         </h2>
         <p class="text">
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.1a0.dev1">coverage.py v7.5.1a0.dev1</a>,
-            created at 2024-04-29 17:40 -0300
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
 </header>
@@ -103,8 +103,8 @@ <h2>
 <footer>
     <div class="content">
         <p>
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.1a0.dev1">coverage.py v7.5.1a0.dev1</a>,
-            created at 2024-04-29 17:40 -0300
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
     <aside class="hidden">

diff --git a/tests/gold/html/partial/partial_py.html b/tests/gold/html/partial/partial_py.html
@@ -66,8 +66,8 @@ <h2>
             <a id="indexLink" class="nav" href="index.html">&Hat; index</a> &nbsp; &nbsp;
             <a id="nextFileLink" class="nav" href="index.html">&#xbb; next</a>
             &nbsp; &nbsp; &nbsp;
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.4a0.dev1">coverage.py v7.5.4a0.dev1</a>,
-            created at 2024-05-30 15:19 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
         <aside class="hidden">
             <button type="button" class="button_next_chunk" data-shortcut="j"></button>
@@ -107,8 +107,8 @@ <h2>
             <a class="nav" href="index.html">&Hat; index</a> &nbsp; &nbsp;
             <a class="nav" href="index.html">&#xbb; next</a>
             &nbsp; &nbsp; &nbsp;
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.5.4a0.dev1">coverage.py v7.5.4a0.dev1</a>,
-            created at 2024-05-30 15:19 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 17:25 -0500
         </p>
     </div>
 </footer>

diff --git a/tests/gold/html/partial_626/class_index.html b/tests/gold/html/partial_626/class_index.html
@@ -11,7 +11,7 @@
 <header>
     <div class="content">
         <h1>Coverage report:
-            <span class="pc_cov">87%</span>
+            <span class="pc_cov">92%</span>
         </h1>
         <aside id="help_panel_wrapper">
             <input id="help_panel_state" type="checkbox">
@@ -56,8 +56,8 @@ <h2>
                 <a class="button current">Classes</a>
         </h2>
         <p class="text">
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.0a0.dev1">coverage.py v7.6.0a0.dev1</a>,
-            created at 2024-07-10 12:20 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 12:46 -0500
         </p>
     </div>
 </header>
@@ -82,9 +82,9 @@ <h2>
                 <td>9</td>
                 <td>0</td>
                 <td>1</td>
-                <td>6</td>
-                <td>2</td>
-                <td class="right" data-ratio="13 15">87%</td>
+                <td>4</td>
+                <td>1</td>
+                <td class="right" data-ratio="12 13">92%</td>
             </tr>
         </tbody>
         <tfoot>
@@ -94,9 +94,9 @@ <h2>
                 <td>9</td>
                 <td>0</td>
                 <td>1</td>
-                <td>6</td>
-                <td>2</td>
-                <td class="right" data-ratio="13 15">87%</td>
+                <td>4</td>
+                <td>1</td>
+                <td class="right" data-ratio="12 13">92%</td>
             </tr>
         </tfoot>
     </table>
@@ -107,8 +107,8 @@ <h2>
 <footer>
     <div class="content">
         <p>
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.0a0.dev1">coverage.py v7.6.0a0.dev1</a>,
-            created at 2024-07-10 12:20 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 12:46 -0500
         </p>
     </div>
     <aside class="hidden">

diff --git a/tests/gold/html/partial_626/function_index.html b/tests/gold/html/partial_626/function_index.html
@@ -11,7 +11,7 @@
 <header>
     <div class="content">
         <h1>Coverage report:
-            <span class="pc_cov">87%</span>
+            <span class="pc_cov">92%</span>
         </h1>
         <aside id="help_panel_wrapper">
             <input id="help_panel_state" type="checkbox">
@@ -56,8 +56,8 @@ <h2>
                 <a class="button" href="class_index.html">Classes</a>
         </h2>
         <p class="text">
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.0a0.dev1">coverage.py v7.6.0a0.dev1</a>,
-            created at 2024-07-10 12:20 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 12:46 -0500
         </p>
     </div>
 </header>
@@ -82,9 +82,9 @@ <h2>
                 <td>9</td>
                 <td>0</td>
                 <td>1</td>
-                <td>6</td>
-                <td>2</td>
-                <td class="right" data-ratio="13 15">87%</td>
+                <td>4</td>
+                <td>1</td>
+                <td class="right" data-ratio="12 13">92%</td>
             </tr>
         </tbody>
         <tfoot>
@@ -94,9 +94,9 @@ <h2>
                 <td>9</td>
                 <td>0</td>
                 <td>1</td>
-                <td>6</td>
-                <td>2</td>
-                <td class="right" data-ratio="13 15">87%</td>
+                <td>4</td>
+                <td>1</td>
+                <td class="right" data-ratio="12 13">92%</td>
             </tr>
         </tfoot>
     </table>
@@ -107,8 +107,8 @@ <h2>
 <footer>
     <div class="content">
         <p>
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.0a0.dev1">coverage.py v7.6.0a0.dev1</a>,
-            created at 2024-07-10 12:20 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 12:46 -0500
         </p>
     </div>
     <aside class="hidden">

diff --git a/tests/gold/html/partial_626/index.html b/tests/gold/html/partial_626/index.html
@@ -11,7 +11,7 @@
 <header>
     <div class="content">
         <h1>Coverage report:
-            <span class="pc_cov">87%</span>
+            <span class="pc_cov">92%</span>
         </h1>
         <aside id="help_panel_wrapper">
             <input id="help_panel_state" type="checkbox">
@@ -55,8 +55,8 @@ <h2>
                 <a class="button" href="class_index.html">Classes</a>
         </h2>
         <p class="text">
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.0a0.dev1">coverage.py v7.6.0a0.dev1</a>,
-            created at 2024-07-10 12:20 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 12:46 -0500
         </p>
     </div>
 </header>
@@ -79,9 +79,9 @@ <h2>
                 <td>9</td>
                 <td>0</td>
                 <td>1</td>
-                <td>6</td>
-                <td>2</td>
-                <td class="right" data-ratio="13 15">87%</td>
+                <td>4</td>
+                <td>1</td>
+                <td class="right" data-ratio="12 13">92%</td>
             </tr>
         </tbody>
         <tfoot>
@@ -90,9 +90,9 @@ <h2>
                 <td>9</td>
                 <td>0</td>
                 <td>1</td>
-                <td>6</td>
-                <td>2</td>
-                <td class="right" data-ratio="13 15">87%</td>
+                <td>4</td>
+                <td>1</td>
+                <td class="right" data-ratio="12 13">92%</td>
             </tr>
         </tfoot>
     </table>
@@ -103,8 +103,8 @@ <h2>
 <footer>
     <div class="content">
         <p>
-            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.0a0.dev1">coverage.py v7.6.0a0.dev1</a>,
-            created at 2024-07-10 12:20 -0400
+            <a class="nav" href="https://coverage.readthedocs.io/en/7.6.13a0.dev1">coverage.py v7.6.13a0.dev1</a>,
+            created at 2025-02-15 12:46 -0500
         </p>
     </div>
     <aside class="hidden">