Add a lint for missing return statements

This lint checks that if a functions returns a value in some execution
paths, it does so in all execution paths.

RELNOTES: None
PiperOrigin-RevId: 166688783

1 files changed, 220 insertions, 0 deletions

diff --git a/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/ControlFlowCheckerTest.java b/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/ControlFlowCheckerTest.java
new file mode 100644
index 0000000000..7e7addd8a2
--- /dev/null
+++ b/src/tools/skylark/javatests/com/google/devtools/skylark/skylint/ControlFlowCheckerTest.java
@@ -0,0 +1,220 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.skylark.skylint;
+
+import com.google.common.truth.Truth;
+import com.google.devtools.build.lib.syntax.BuildFileAST;
+import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class ControlFlowCheckerTest {
+  private static List<Issue> findIssues(String... lines) {
+    String content = String.join("\n", lines);
+    BuildFileAST ast =
+        BuildFileAST.parseSkylarkString(
+            event -> {
+              throw new IllegalArgumentException(event.getMessage());
+            },
+            content);
+    return ControlFlowChecker.check(ast);
+  }
+
+  @Test
+  public void testIfElseReturnMissing() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                    "def some_function(x):",
+                    "  if x:",
+                    "    print('foo')",
+                    "  else:",
+                    "    return x")
+                .toString())
+        .contains("some but not all execution paths of 'some_function' return a value");
+  }
+
+  @Test
+  public void testIfElseReturnValueMissing() throws Exception {
+    String messages =
+        findIssues(
+                "def some_function(x):",
+                "  if x:",
+                "    return x",
+                "  else:",
+                "    return # missing value")
+            .toString();
+    Truth.assertThat(messages)
+        .contains("some but not all execution paths of 'some_function' return a value");
+    Truth.assertThat(messages).contains(":5:5: return value missing");
+  }
+
+  @Test
+  public void testIfElifElseReturnMissing() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                    "def f(x):",
+                    "  if x:",
+                    "    return x",
+                    "  elif not x:",
+                    "    pass",
+                    "  else:",
+                    "    return not x")
+                .toString())
+        .contains("some but not all execution paths of 'f' return a value");
+  }
+
+  @Test
+  public void testNestedIfElseReturnMissing() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                    "def f(x, y):",
+                    "  if x:",
+                    "    if y:",
+                    "      return y",
+                    "    else:",
+                    "      print('foo')",
+                    "  else:",
+                    "    return x")
+                .toString())
+        .contains("some but not all execution paths of 'f' return a value");
+  }
+
+  @Test
+  public void testElseBranchMissing() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                    "def some_function(x):",
+                    "  if x:",
+                    "    return x",
+                    "  elif not x:",
+                    "    return not x")
+                .toString())
+        .contains("some but not all execution paths of 'some_function' return a value");
+  }
+
+  @Test
+  public void testIfAndFallOffEnd() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                    "def some_function(x):",
+                    "  if x:",
+                    "    return x",
+                    "  print('foo')",
+                    "  # return missing here")
+                .toString())
+        .contains("some but not all execution paths of 'some_function' return a value");
+  }
+
+  @Test
+  public void testAlwaysReturnButSometimesWithoutValue() throws Exception {
+    String messages =
+        findIssues(
+                "def some_function(x):",
+                "  if x:",
+                "    return # returns without value here",
+                "  return x")
+            .toString();
+    Truth.assertThat(messages)
+        .contains("some but not all execution paths of 'some_function' return a value");
+    Truth.assertThat(messages).contains(":3:5: return value missing");
+  }
+
+  @Test
+  public void testIfBeforeReturn() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                "def f(x, y):",
+                "  if x:",
+                "    return x",
+                "  elif not y:",
+                "    print('foo')",
+                "  print('bar')",
+                "  return y"))
+        .isEmpty();
+  }
+
+  @Test
+  public void testReturnInAllBranches() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                "def f(x, y):",
+                "  if x:",
+                "    return x",
+                "  elif not y:",
+                "    return None",
+                "  else:",
+                "    return y"))
+        .isEmpty();
+  }
+
+  @Test
+  public void testReturnInNestedIf() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                "def f(x,y):",
+                "  if x:",
+                "    if y:",
+                "      return y",
+                "    else:",
+                "      return not y",
+                "  else:",
+                "    return not x"))
+        .isEmpty();
+  }
+
+  @Test
+  public void testIfStatementSequence() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                "def f(x,y):",
+                "  if x:",
+                "    print('foo')",
+                "  else:",
+                "    return x",
+                "  print('bar')",
+                "  if y:",
+                "    return x",
+                "  else:",
+                "    return y"))
+        .isEmpty();
+    Truth.assertThat(
+            findIssues(
+                "def f(x,y):",
+                "  if x:",
+                "    return x",
+                "  else:",
+                "    return x",
+                "  # from now on everything's unreachable",
+                "  print('bar')",
+                "  if y:",
+                "    return x",
+                "  # no else branch but doesn't matter since it's unreachable"))
+        .isEmpty();
+  }
+
+  @Test
+  public void testCallToFail() throws Exception {
+    Truth.assertThat(
+            findIssues(
+                "def some_function_name(x):",
+                "  if x:",
+                "    fail('bar')",
+                "  else:",
+                "    return x"))
+        .isEmpty();
+  }
+}