Introduce `DirectReturn` check #513

Stephan202 · 2023-02-26T16:09:17Z

This PR replaces #1. I decided to pick this task up because the topic was raised after @rickie's recent Amsterdam JUG presentation. CC @SimonBaars.

Suggested commit message:

Introduce `DirectReturn` check (#513)

github-actions · 2023-02-26T16:11:50Z

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🎉`tech.picnic.errorprone.bugpatterns.DirectReturn`	0	26

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Stephan202 · 2023-02-26T16:11:56Z

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/DirectReturn.java

+    linkType = CUSTOM,
+    severity = SUGGESTION,
+    tags = SIMPLIFICATION)
+public final class DirectReturn extends BugChecker implements BlockTreeMatcher {


Naming-wise, "something something unnecessary assignment" may be nicer. But (a) we're not performing a flow analysis that flags all unnecessary variable assignments and (b) a name that accurately describes the subset covered would be quite unwieldy. Unless I'm just not creative enough, of course 🙃. Suggestions welcome.

Stephan202 · 2023-03-06T05:28:02Z

Just realized: ideally we do not suggest inlining if (a) the variable assigned to is of a different type than the method's return type and (b) this difference may influence the return value. Prime example here is Mockito's nullary mock() method (see also #454). I'll come back to this PR to see how we can best cover this case.

Stephan202 · 2023-03-11T20:03:01Z

Rebased and added a commit to cover this case. Did make it Mockito-specifc, because attempts at generalization became too contrived.

github-actions · 2023-03-11T20:05:33Z

Looks good. All 51 mutations in this change were killed.

class	surviving	killed
🎉`tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers`	0	5
🎉`tech.picnic.errorprone.bugpatterns.DirectReturn`	0	34
🎉`tech.picnic.errorprone.bugpatterns.MockitoMockClassReference`	0	12

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Stephan202

Added one more commit.

Stephan202 · 2023-03-12T09:27:43Z

...rone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/MockitoMockClassReference.java

@@ -49,7 +48,7 @@
 public final class MockitoMockClassReference extends BugChecker


CC @Badbond: I renamed/moved some logic in this class.

Stephan202 · 2023-03-12T09:28:52Z

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/MoreASTHelpers.java

+  public static Optional<MethodTree> findMethodExitedOnReturn(VisitorState state) {
+    return Optional.ofNullable(state.findEnclosing(LambdaExpressionTree.class, MethodTree.class))
+        .filter(MethodTree.class::isInstance)
+        .map(MethodTree.class::cast);
+  }


I decided to move this out because it handles quite a gotcha; better to not duplicate this logic.

github-actions · 2023-03-12T10:03:37Z

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🎉`tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers`	0	5
🎉`tech.picnic.errorprone.bugpatterns.DirectReturn`	0	34
🎉`tech.picnic.errorprone.bugpatterns.MockitoMockClassReference`	0	12

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rickie

Flushing one comment I had. Will continue later today.

rickie · 2023-03-27T18:59:18Z

...-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/MoreASTHelpersTest.java

+        .addSourceLines(
+            "A.java",
+            "class A {",
+            "  void negative1(String a, Integer b) {}",


Might be good to add a test where one is a subtype of the other? (Will add this in a commit)

werli

The code itself and the added test cases were rather straightforward, nice work @Stephan202 👍

One more point about the exhaustiveness of the mockito exclusion, but I wouldn't expect more changes here as part of this PR. Hence I'm approving.

werli · 2023-03-30T15:28:03Z

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/DirectReturn.java

+   * <p>Inlining is generally safe, but in rare cases the operation may have a functional impact.
+   * The sole case considered here is the inlining of a Mockito mock or spy construction without an
+   * explicit type. In such a case the type created depends on context, such as the method's return
+   * type.


Great to have added this exclusion. Are we sure the exclusion is exhaustive however? My guess is: probably never fully, but this is a best-effort solution that should handle the majority of EPS users.

Nope, this is not exhaustive, unfortunately. I did play with some more generic code, but it became way more complex than I could justify for this feature. So in the end gave up on that idea.

Stephan202

Tnx for the reviews!

Stephan202 · 2023-03-30T16:36:47Z

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/DirectReturn.java

+   * <p>Inlining is generally safe, but in rare cases the operation may have a functional impact.
+   * The sole case considered here is the inlining of a Mockito mock or spy construction without an
+   * explicit type. In such a case the type created depends on context, such as the method's return
+   * type.


Nope, this is not exhaustive, unfortunately. I did play with some more generic code, but it became way more complex than I could justify for this feature. So in the end gave up on that idea.

rickie

Really cool check 🚀.

Have some small comments and an extra test case or two. Let me know what you think 😄.

rickie · 2023-03-30T18:06:44Z

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/DirectReturnTest.java

+            "    return variable;",
+            "  }",
+            "",
+            "  Object salienSpyTypeVariableDeclaration() {",


Suggested change

" Object salienSpyTypeVariableDeclaration() {",

" Object salientSpyTypeVariableDeclaration() {",

rickie · 2023-03-30T18:19:06Z

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/DirectReturnTest.java

+            "      // BUG: Diagnostic contains:",
+            "      variable = \"foo\";",
+            "      return variable;",
+            "    }",


I think this is also an interesting case to add:

Supplier<String> redundantAssignmentInLambda() { return () -> { // BUG: Diagnostic contains: String variable = toString(); return variable; };

rickie · 2023-03-30T18:20:17Z

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/MoreASTHelpers.java

@@ -46,4 +50,33 @@ public static ImmutableList<MethodTree> findMethods(CharSequence methodName, Vis
  public static boolean methodExistsInEnclosingClass(CharSequence methodName, VisitorState state) {
    return !findMethods(methodName, state).isEmpty();
  }
+
+  /**
+   * Returns the {@link MethodTree} from which control flow would exit if there would be a {@code


Suggested change

* Returns the {@link MethodTree} from which control flow would exit if there would be a {@code

* Returns the {@link MethodTree} from which the control flow would exit if there would be a {@code

Sounds a bit better to me 🤔.

github-actions · 2023-03-30T18:27:08Z

Looks good. All 51 mutations in this change were killed.

class	surviving	killed
🎉`tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers`	0	5
🎉`tech.picnic.errorprone.bugpatterns.DirectReturn`	0	34
🎉`tech.picnic.errorprone.bugpatterns.MockitoMockClassReference`	0	12

Mutation testing report by Pitest. Review any surviving mutants by inspecting the line comments under Files changed.

rickie · 2023-03-30T18:28:43Z

Aii, misclicked and merged instead of rebased 😅.

github-actions · 2023-03-30T18:31:21Z

Looks good. All 51 mutations in this change were killed.

class	surviving	killed
🎉`tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers`	0	5
🎉`tech.picnic.errorprone.bugpatterns.DirectReturn`	0	34
🎉`tech.picnic.errorprone.bugpatterns.MockitoMockClassReference`	0	12

Mutation testing report by Pitest. Review any surviving mutants by inspecting the line comments under Files changed.

Stephan202

Tnx; changes LGTM otherwise

Stephan202 · 2023-03-30T18:33:25Z

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/MoreASTHelpers.java

@@ -46,4 +50,33 @@ public static ImmutableList<MethodTree> findMethods(CharSequence methodName, Vis
  public static boolean methodExistsInEnclosingClass(CharSequence methodName, VisitorState state) {
    return !findMethods(methodName, state).isEmpty();
  }
+
+  /**
+   * Returns the {@link MethodTree} from which the control flow would exit if there would be a


I think we should omit "the" here. (Cause this is not about a "definite" control flow.)

Stephan202 · 2023-03-30T18:34:41Z

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/DirectReturnTest.java

+            "    }",
+            "  }",
+            "",
+            "  Supplier<String> redundantAssignmentInLambda() {",


Suggested change

" Supplier<String> redundantAssignmentInLambda() {",

" Supplier<String> redundantAssignmentInsideLambda() {",

Also matches the method above.

rickie · 2023-03-30T18:42:46Z

Applied and rebased. Will merge once 🟢, thanks for taking a look so quickly.

Stephan202 · 2023-03-30T18:43:29Z

Let's gooooo 🚀

github-actions · 2023-03-30T18:45:19Z

Looks good. All 51 mutations in this change were killed.

class	surviving	killed
🎉`tech.picnic.errorprone.bugpatterns.util.MoreASTHelpers`	0	5
🎉`tech.picnic.errorprone.bugpatterns.DirectReturn`	0	34
🎉`tech.picnic.errorprone.bugpatterns.MockitoMockClassReference`	0	12

Mutation testing report by Pitest. Review any surviving mutants by inspecting the line comments under Files changed.

Stephan202 added this to the 0.9.0 milestone Feb 26, 2023

Stephan202 requested a review from rickie February 26, 2023 16:09

Stephan202 commented Feb 26, 2023

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Stephan202 mentioned this pull request Feb 26, 2023

When variables are assigned then returned, instead directly return them #1

Closed

Stephan202 force-pushed the sschroevers/inline-variable-return-statements branch from b3c41d7 to 120e418 Compare March 11, 2023 20:02

Stephan202 commented Mar 12, 2023

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werli self-requested a review March 30, 2023 12:27

rickie reviewed Mar 30, 2023

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werli approved these changes Mar 30, 2023

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Stephan202 commented Mar 30, 2023

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rickie approved these changes Mar 30, 2023

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rickie added the new feature label Mar 30, 2023

Stephan202 commented Mar 30, 2023

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Stephan202 and others added 5 commits March 30, 2023 20:42

Introduce DirectReturn check

4aca597

Handle mock statements

cec2ac9

Improve test

c974ea0

Suggestions

143393f

Tweaks

2507a85

rickie force-pushed the sschroevers/inline-variable-return-statements branch from 10ddbf3 to 2507a85 Compare March 30, 2023 18:42

rickie merged commit 73cf28e into master Mar 30, 2023
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rickie deleted the sschroevers/inline-variable-return-statements branch March 30, 2023 18:51

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Introduce `DirectReturn` check #513

Introduce `DirectReturn` check #513

Stephan202 commented Feb 26, 2023 •

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		@@ -49,7 +48,7 @@
		public final class MockitoMockClassReference extends BugChecker

	" Object salienSpyTypeVariableDeclaration() {",
	" Object salientSpyTypeVariableDeclaration() {",

	* Returns the {@link MethodTree} from which control flow would exit if there would be a {@code
	* Returns the {@link MethodTree} from which the control flow would exit if there would be a {@code

	" Supplier<String> redundantAssignmentInLambda() {",
	" Supplier<String> redundantAssignmentInsideLambda() {",

Introduce DirectReturn check #513

Introduce DirectReturn check #513

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Introduce `DirectReturn` check #513

Introduce `DirectReturn` check #513

Stephan202 commented Feb 26, 2023 •

edited