transformer: define does not share reference for objects

[sapphi-red]

esbuild try

#[test]
fn same_reference_for_object() {
    let config =
        ReplaceGlobalDefinesConfig::new(&[("__OBJ__", r#"{"vars":{"SOMEVAR":"foo"}}"#)])
            .unwrap();
    test(
        "
        console.log(__OBJ__.vars);
        __OBJ__.vars.ANOTHER = 'bar';
        console.log(__OBJ__.vars)",
        "
        const __OBJ__ = {vars:{SOMEVAR:\"foo\"}};
        console.log(__OBJ__.vars);
        __OBJ__.vars.ANOTHER = 'bar';
        console.log(__OBJ__.vars)",
        config.clone(),
    ); // fails
}

Oxc outputs:

console.log({ 'vars': { 'SOMEVAR': 'foo' } }.vars);
({ 'vars': { 'SOMEVAR': 'foo' } }).vars.ANOTHER = 'bar';
console.log({ 'vars': { 'SOMEVAR': 'foo' } }.vars);

This has a different behavior.

[sapphi-red]

I'm not sure how many people relies on this behavior though

[IWANABETHATGUY]

after investigation,

• webpack DefinePlugin: don't share object
• rollup: AFAIK they don't have the official define plugin(they have replace plugin based on string), don't support share object.
• oxc define: don't share object
• esbuild define: create a share object

So I am wondering if it is necessary to add this feature.

[sapphi-red]

It seems the reason was to reduce the bundle size rather than sharing the reference itself. evanw/esbuild#581
I don't think it's a necessary thing, but I guess it'd be difficult to introduce this behavior later on as an optimization, as it changes the behavior.

[IWANABETHATGUY]

I see

[Boshen]

I want to reject this feature for now and evaluate the requirement when it is bought up again.

The motivation and discussion in evanw/esbuild#581 is still unclear to me, and the I can't find any real examples of people using this feature.

And also, the behaviour of esbuild documented in evanw/esbuild@a5288c6#diff-f312cd3ffe8d88cf424d3f0bd04b41e5b0ad36e549874b5688028bf9091a61f5R967 is

This release adds support for array and object literals with --define anyway, but they work differently than other --define expressions. In this case a separate virtual file is created and configured to be injected into all files similar to how the --inject feature works. This means there is only at most one copy of the value in a given output file. However, these values do not participate in constant folding and dead code elimination, since the object can now potentially be mutated at run-time.

Personally, this feature is really confusing in the scope of the define plugin, which makes it behave like an automated inject plugin.

Let's revisit this requirement again when it is bought up again by a consumer.

[Boshen]

I'm going to close this as not planned for now, feel free to bring this up again when there is an actual requirement.