[Gradle] Track 'webMain' sources usage

^KT-79482 In Progress

Author: Tapchicoma

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/statistics/FusMetrics.kt

@@ -403,6 +403,7 @@ internal object KotlinSourceSetMetrics : FusMetrics {
     internal fun collectMetrics(project: Project) {
         project.launchInStage(KotlinPluginLifecycle.Stage.AfterFinaliseDsl) {
             project.reportGeneratedSourcesUsage()
+            project.reportWebMainSourceSetUsage()
         }
     }
 
@@ -415,4 +416,16 @@ internal object KotlinSourceSetMetrics : FusMetrics {
             }
         }
     }
+
+    private suspend fun Project.reportWebMainSourceSetUsage() {
+        project.kotlinExtension.awaitSourceSets().configureEach {
+            if (it.name == "webMain") {
+                if (!it.allKotlinSources.isEmpty) {
+                    project.addConfigurationMetrics {
+                        it.put(BooleanMetrics.KOTLIN_WEB_MAIN_SOURCES_USED, true)
+                    }
+                }
+            }
+        }
+    }
 }

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/fus/FUSWebMainSourceSetTest.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2010-2025 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.unitTests.fus
+
+import org.gradle.kotlin.dsl.get
+import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
+import org.jetbrains.kotlin.gradle.dsl.multiplatformExtension
+import org.jetbrains.kotlin.gradle.util.buildProjectWithMPP
+import org.jetbrains.kotlin.statistics.metrics.BooleanMetrics
+import kotlin.test.Test
+import kotlin.test.assertNotNull
+
+@OptIn(ExperimentalWasmDsl::class)
+class FUSWebMainSourceSetTest {
+
+    @Test
+    fun emptyWebMainSourcesAreNotReported() {
+        val project = buildProjectWithMPP(preApplyCode = enableFusOnCI) {
+            with(multiplatformExtension) {
+                js { nodejs() }
+                wasmJs()
+            }
+        }
+
+        project.evaluate()
+
+        assertNotNull(
+            project.collectedFusConfigurationTimeMetrics.booleanMetrics.keys.none {
+                it.name == BooleanMetrics.KOTLIN_WEB_MAIN_SOURCES_USED.name
+            },
+            "FUS event is present for webMain sources"
+        )
+    }
+
+    @Test
+    fun explicitlyAddedWebMainSourcesAreReported() {
+        val project = buildProjectWithMPP(preApplyCode = enableFusOnCI) {
+            with(multiplatformExtension) {
+                js { browser() }
+                wasmJs { browser() }
+            }
+        }
+
+        val sharedFile = project.layout.projectDirectory.file("src/webMain/kotlin/shared.kt").asFile
+        sharedFile.parentFile.mkdirs()
+        sharedFile.writeText("fun shared() = 1")
+
+        project.evaluate()
+
+        assertNotNull(
+            project.collectedFusConfigurationTimeMetrics.booleanMetrics.entries.singleOrNull {
+                it.key == BooleanMetrics.KOTLIN_WEB_MAIN_SOURCES_USED && it.value
+            }
+        )
+    }
+}

libraries/tools/kotlin-gradle-statistics/src/main/kotlin/org/jetbrains/kotlin/statistics/metrics/BooleanMetrics.kt

@@ -47,7 +47,9 @@ enum class BooleanMetrics(val type: BooleanOverridePolicy, val anonymization: Bo
     KOTLIN_PROGRESSIVE_MODE(OVERRIDE, SAFE),
     KOTLIN_KTS_USED(OR, SAFE),
     KOTLIN_BTA_USED(OR, SAFE),
+
     KOTLIN_GENERATED_SOURCES_USED(OR, SAFE),
+    KOTLIN_WEB_MAIN_SOURCES_USED(OR, SAFE),
 
     // Disabled explicitly by the user
     KOTLIN_CROSS_COMPILATION_DISABLED(OR, SAFE),
@@ -127,6 +129,6 @@ enum class BooleanMetrics(val type: BooleanOverridePolicy, val anonymization: Bo
     ;
 
     companion object {
-        const val VERSION = 20
+        const val VERSION = 21
     }
 }