Proposal prefer_const_unmodified_static_declarations

[FMorschel]

Describe the issue
With the folwing code:

class A {
  const A();

  static A a = A();
}

We get a warning for the const keyword at the constructor in line 4.

After placing it there, it doesn't warn about the static A a declaration being possibly constant.

Expected behavior
Warn at the static declaration that a variable can be const.

[bwilkerson]

I suspect that this would want to be a separate lint as it would probably want to flag any static final field whose initializer is a constant expression.

I included 'final' in the description above because changing a variable (especially a public variable) from static to static const is a significant change. If the field is already final then changing it to const is mostly just an optimization.

[FMorschel]

I included 'final' in the description above because changing a variable (especially a public variable) from static to static const is a significant change.

So if the static variable is private or if the class itself is private the lint could show. I agree.

I'm not so good in naming things and I can't seem to find your issue on naming lints (for wording and stuff - saw it once when browsing here) so I'll let others suggest a name for it.

Edit

I suspect the name of the lint on the title won't let you remove the tag.

Edit 2

Found the docs for that https://github.com/dart-lang/linter/blob/main/doc/writing-lints.md#lint-properties. Will think of a name later, just wanted to place it here for reference.

[FMorschel]

prefer_const_unmodified_static_declarations

Description

Should use const for static variables that are declared as final but are initialized with a constant value.

Details

Promoting the practice of marking static variables as const instead of final when they are initialized with a constant value. Using const ensures that the variables are compile-time constants, which can improve performance and code clarity by avoiding unnecessary allocations and guaranteeing immutability.

Kind

This rule enforces style advice and promotes code optimization by encouraging the use of const for static variables that are unmodified.

Bad Examples

static final myList = const [1, 2, 3];
static final myMap = const {'key': 'value'};

Good Examples

static const myList = [1, 2, 3];
static const myMap = {'key': 'value'};

Discussion

This proposal addresses a gap in the current Dart lints by targeting static final variables that could be declared as const. By ensuring that these variables are declared as const where applicable, the lint helps prevent missed opportunities for optimization and promotes clearer, more maintainable code.

I believe this should be added to Effective Dart. Since it is an extension of prefer_const_declarations.

Discussion checklist

• List any existing rules this proposal modifies, complements, overlaps or conflicts with.
• List any relevant issues (reported here, the [SDK Tracker], or elsewhere).
• If there's any prior art (e.g., in other linters), please add references here.
• If this proposal corresponds to [Effective Dart] or [Flutter Style Guide] advice, please call it out. (If there isn't any corresponding advice, should there be?)
• If this proposal is motivated by real-world examples, please provide as many details as you can. Demonstrating potential impact is especially valuable.

[bwilkerson]

@munificent (For the suggestion of adding this to Effective Dart.)

[munificent]

If the field is already final then changing it to const is mostly just an optimization.

Mostly, but it does mean that the author of that API is committing to that static field being usable in constant expressions and it becomes a breaking API change to remove the const.