[Clemens Koprolin (clemenskoprolin)]

Introduces a JVM compiler plugin that prepares static HTML at compile time and replaces supported composables with direct writer calls. Dynamic values remain escaped at runtime, unsupported calls retain normal rendering.

E.g.:

@Composable
fun Welcome() {
    Div {
        H1 { Text("Hello!") }
        P { Text("Welcome to Compose HTML.") }
    }
}

Becomes the equivalent of:

@Composable
fun Welcome() {
    WriteStaticHtml("div", "<div><h1>Hello!</h1><p>Welcome to Compose HTML.</p></div>")
}

With dynamic text instead:

@Composable
fun Greeting(name: String) {
    Div {
        Span { Text("Hello, ") }
        Text(name)
    }
}

it becomes equivalent of:

@Composable
fun Greeting(name: String) {
    val writer = currentHtmlStringWriter()
    val strict = currentHtmlValidationIsStrict()
    val parent = writer.openLoweredRegion(
        rootTag = "div",
        encoded = "<div><span>Hello, </span>",
        innermost = "div",
        validate = strict,
    )
    writer.writeText(name, strict)
    writer.closeElement("</div>", parent)
}

Supported lowering includes:

• Static HTML/SVG subtrees and constant repeat bodies → precomputed HTML literals.
• Mixed static markup and dynamic text → direct writer calls with runtime escaping.
• Constant and dynamic attributes, classes, styles and form values → prepared attributes or direct serialization.
• Built-in wrappers, direct TagElement calls and custom wrappers annotated with @LowerableHtmlTag → optimized writer calls where supported.
• Supported constant expressions and immutable aliases → compile-time values

Includes a Gradle plugin, shared serialization rules and JVM bytecode and browser hydration tests. Prepared static HTML can retain text-boundary comments when hydratable = false.

Involves CMP-10991 and CMP-10836

Testing

Run from the html directory:

./gradlew -p eap/compiler-plugin -Pcompose.html.eap.enabled=true \
  check \
  :html:html-core-eap:jvmTest \
  :html:html-core-eap:jsTest \
  :html:html-core-eap:wasmJsTest

Release Notes

N/A

[Oleksandr Karpovich (eymar)]

When editing those files, it's not obvious that they are used here in the compiler plugin implementation.

What do you think about extracting html-serialization-related helpers into a separate module and adding it as a usual dependency here?
The problem is that most of the helpers are "internal" and ideally they remain "internal". But for our needs it's fine to suppress the usages.

[Oleksandr Karpovich (eymar)]

Could the compiler plugin be included directly in the root settings?
Any reason why it's a standalone gradle project?

[Oleksandr Karpovich (eymar)]

Why not write directly to HtmlStringWriterContext ? Why is the field necessary?

[Oleksandr Karpovich (eymar)]

Let's keep just one property?

val enabledTargets: SetProperty< KotlinPlatformType>

With Jvm enabled by default

[Oleksandr Karpovich (eymar)]

As I see, this and some other tests pass even when the compiler plugin is disabled.

After this PR, I think it's worth to implement tests comparing the generated IR with the golden one.
Here is an example from Compose compiler plugin tests - https://github.com/JetBrains/kotlin/blob/de4aa1dfb1546fc83006f5833c5dce24948ebfc3/plugins/compose/compiler-hosted/integration-tests/testResources/golden/androidx.compose.compiler.plugins.kotlin.ClassStabilityTransformTests/testComposableCall.txt

Seeing such IR golden snippets help understand what the compiler plugin is supposed to do in every case.

[Oleksandr Karpovich (eymar)]

Could you please reformat the files in this PR?

https://www.jetbrains.com/help/idea/reformat-and-rearrange-code.html#reformat_file (Cmd+option+shift+L)

It won't reformat these nested loops, so to make it more readable could you please format it manually?

internal inline fun forEachRenderMode(test: (strict: Boolean, hydratable: Boolean, stream: Boolean) -> Unit) {
    val variants = listOf(false, true)
    for (strict in variants) {
        for (hydratable in variants) {
            for (stream in variants) {
                test(strict, hydratable, stream)
            }
        }
    }
}

Perhaps in other places too.