Warn when `open` modifier is redundant (traits, abstract classes and local classes) #11971

megri · 2021-04-01T21:05:16Z

#11963

A first draft to I make sure I'm on the right path. I'd like to establish that my thinking/coding style is correct as well. :)

smarter

I'd like to establish that my thinking/coding style is correct as well

Yeah that's fine, the only nitpick I have is that the first line of your commit message should be more descriptive (e.g. "Disallow open modifier when redundant"), in the body of the commit message you can then write Fixes #11963 (it needs to be in this format for the issue to be auto-closed by github when the PR is merged).

smarter · 2021-04-01T21:43:00Z

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -2505,3 +2505,10 @@ import transform.SymUtils._
          |Inlining such definition would multiply this footprint for each call site.
          |""".stripMargin
  }
+
+  class OpenModifierRedundantForAbstractClassOrTrait(cls: untpd.TypeDef, isTrait: Boolean)(using Context)


Instead of defining a new message class, it might be possible to generalize the existing ModifierRedundantForObjects class to a ModifierRedundant that can be used for non-classes too.

I would need to disambiguate between abstract/inner classes, traits and objects. Should this be done on an untpd.Tree or is there a more suitable abstraction?

edit: maybe an union type of untpd.ModuleDef | untpd.TypeDef ?

Looks like the cls argument isn't used here and could just be removed

It would be nice to keep the explain-method from ModifierRedundantForObjects around and generalise it. I could pass the information from the report site as a String but I think it'd richer information would be preferable, right?

I patched the functionality a bit. It would be nice if the recommended solution in explain kept the template (or lack thereof) around, but for large defs that would be spammy unless truncated.

smarter · 2021-04-02T11:30:42Z

(I'm taking some time off so I won't be available to review this PR this week or the next)

odersky · 2021-04-06T10:13:09Z

I fear it's overengineered. A fix like this should cost inside of 5 lines of code. Everything else should be discussed separately.

In my experience flag checking can easily explode in complexity which makes it unmaintainable. It needs to be reigned in by design from the start.

megri · 2021-04-06T12:03:12Z

I fear it's overengineered. A fix like this should cost inside of 5 lines of code. Everything else should be discussed separately.

In my experience flag checking can easily explode in complexity which makes it unmaintainable. It needs to be reigned in by design from the start.

Fair enough. I'll remove the enum and reduce the surface area. My only remaining concern is how to keep the error explanation nice and relevant.

edit: I have pushed the changes

odersky · 2021-04-06T15:56:40Z

Flags checking is a bit of a mess, I am afraid, so I am not sure this was a good first issue after all.

In fact, all flags should be checked in Checking.checkWellformed. The flags checking code in Desugar should really be the exception. It has to do with the fact that original flags are added and suppressed by Desugaring, which means flags had to be checked before. But we should not generalize this.

megri · 2021-04-06T16:49:04Z

Flags checking is a bit of a mess, I am afraid, so I am not sure this was a good first issue after all.

In fact, all flags should be checked in Checking.checkWellformed. The flags checking code in Desugar should really be the exception. It has to do with the fact that original flags are added and suppressed by Desugaring, which means flags had to be checked before. But we should not generalize this.

The original intention was to give a warning in this case, but it seems checkWellFormed raises errors. Does this change the story or the intended location of the code?

Having come this far, unless there's a desire to have someone more experienced handle this, I'd like to continue working on the issue.

odersky · 2021-04-07T08:38:47Z

The original intention was to give a warning in this case, but it seems checkWellFormed raises errors. Does this change the story or the intended location of the code?

No. checkWellFormed can also do warnings.

Having come this far, unless there's a desire to have someone more experienced handle this, I'd like to continue working on the issue.

OK, great! Since I was looking at the code I have done some refactorings and moved the module checking code from Desugar to Checking, so that others will not be tempted to add to checking code in Desugar. So you'll need to rebase.

megri · 2021-04-07T17:25:44Z

The original intention was to give a warning in this case, but it seems checkWellFormed raises errors. Does this change the story or the intended location of the code?

No. checkWellFormed can also do warnings.

Having come this far, unless there's a desire to have someone more experienced handle this, I'd like to continue working on the issue.

OK, great! Since I was looking at the code I have done some refactorings and moved the module checking code from Desugar to Checking, so that others will not be tempted to add to checking code in Desugar. So you'll need to rebase.

Great, thanks :)

megri · 2021-04-09T06:58:48Z

I think this is ready for final review

smarter · 2021-04-19T07:36:22Z

compiler/src/dotty/tools/dotc/typer/Checking.scala

+        warn(RedundantModifier(Open))
+    if sym.isAllOf(Abstract | Open) then
+      warn(RedundantModifier(Open))
+    if sym.is(Open) && sym.owner.is(Method) then


This can be generalized to:

Suggested change

if sym.is(Open) && sym.owner.is(Method) then

if sym.is(Open) && sym.isLocal then

To also include val owners, local class owner, etc.

Fixes scala#11963

smarter

LGTM, thanks!

smarter reviewed Apr 1, 2021

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megri force-pushed the issue-11963 branch 5 times, most recently from e4bcccb to 1fcdc61 Compare April 2, 2021 09:38

megri marked this pull request as draft April 2, 2021 22:49

megri force-pushed the issue-11963 branch 4 times, most recently from 9f89d7a to 406a370 Compare April 6, 2021 12:31

megri force-pushed the issue-11963 branch from 406a370 to cd2686d Compare April 7, 2021 19:58

megri marked this pull request as ready for review April 7, 2021 20:09

megri changed the title ~~fix issue 11963~~ Warn when open modifier is redundant (traits, abstract classes and local classes) Apr 7, 2021

megri force-pushed the issue-11963 branch from cd2686d to 01eaefa Compare April 7, 2021 20:24

smarter requested changes Apr 19, 2021

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smarter assigned megri Apr 19, 2021

Warn for usage of open modifier on traits or classes where redundant

c6deecd

Fixes scala#11963

megri force-pushed the issue-11963 branch from 01eaefa to c6deecd Compare April 19, 2021 08:31

smarter approved these changes Apr 19, 2021

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smarter enabled auto-merge April 19, 2021 08:39

smarter merged commit dede682 into scala:master Apr 19, 2021

Kordyjan added this to the 3.0.1 milestone Aug 2, 2023

	if sym.is(Open) && sym.owner.is(Method) then
	if sym.is(Open) && sym.isLocal then

Warn when open modifier is redundant (traits, abstract classes and local classes) #11971

Warn when open modifier is redundant (traits, abstract classes and local classes) #11971

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Warn when `open` modifier is redundant (traits, abstract classes and local classes) #11971

Warn when `open` modifier is redundant (traits, abstract classes and local classes) #11971

megri commented Apr 1, 2021 •

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megri commented Apr 6, 2021 •

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