Refactor Detekt task to use staged files (#5705)

README.md

@@ -62,6 +62,37 @@
     - Hit `Download`.
     - Hit `Apply`.
 
+5. Setup `detekt` pre-commit hook (optional):
+
+Run the following script from the root of the repository to install the hook. This will overwrite any existing pre-commit hook if present.
+
+```shell
+echo "Writing detekt pre-commit hook..."
+cat << 'EOL' > .git/hooks/pre-commit
+#!/usr/bin/env bash
+
+echo "Running detekt check..."
+OUTPUT="/tmp/detekt-$(date +%s)"
+./gradlew -Pprecommit=true detekt > $OUTPUT
+EXIT_CODE=$?
+if [ $EXIT_CODE -ne 0 ]; then
+  cat $OUTPUT
+  rm $OUTPUT
+  echo "***********************************************"
+  echo "                 detekt failed                 "
+  echo " Please fix the above issues before committing "
+  echo "***********************************************"
+  exit $EXIT_CODE
+fi
+rm $OUTPUT
+EOL
+echo "detekt pre-commit hook written to .git/hooks/pre-commit"
+echo "Making the hook executable"
+chmod +x .git/hooks/pre-commit
+
+echo "detekt pre-commit hook installed successfully to .git/hooks/pre-commit"
+```
+
 ## Theme
 
 ### Icons & Illustrations

build.gradle.kts

@@ -1,3 +1,5 @@
+import io.gitlab.arturbosch.detekt.Detekt
+
 plugins {
     alias(libs.plugins.android.application) apply false
     alias(libs.plugins.android.library) apply false
@@ -129,10 +131,57 @@ tasks {
         dependsOn("koverXmlReportMergedCoverage")
     }
 
-    withType<io.gitlab.arturbosch.detekt.Detekt>().configureEach {
+    withType<Detekt>().configureEach {
         jvmTarget = libs.versions.jvmTarget.get()
+        // If run as a precommit hook, only run on staged files.
+        // This can be manually trigger by adding `-Pprecommit=true` to the gradle command.
+        if (project.hasProperty("precommit")) {
+            val rootDir = project.rootDir
+            val projectDir = projectDir
+
+            val fileCollection = files()
+
+            setSource(
+                getGitStagedFiles(rootDir)
+                    .map { stagedFiles ->
+                        val stagedFilesFromThisProject = stagedFiles
+                            .filter { it.startsWith(projectDir) }
+
+                        fileCollection.setFrom(*stagedFilesFromThisProject.toTypedArray())
+
+                        fileCollection.asFileTree
+                    },
+            )
+        }
     }
     withType<io.gitlab.arturbosch.detekt.DetektCreateBaselineTask>().configureEach {
         jvmTarget = libs.versions.jvmTarget.get()
     }
 }
+
+/**
+ * Gets the staged files in the current Git repository.
+ */
+fun Project.getGitStagedFiles(rootDir: File): Provider<List<File>> {
+    return providers
+        .exec { commandLine("git", "--no-pager", "diff", "--name-only", "--cached") }
+        .standardOutput.asText
+        .map { outputText ->
+            outputText
+                .trim()
+                .split("\n")
+                .filter { it.isNotBlank() }
+                .map { File(rootDir, it) }
+        }
+}
+
+afterEvaluate {
+    tasks.withType(Detekt::class.java).configureEach {
+        val typeResolutionEnabled = !classpath.isEmpty
+        if (typeResolutionEnabled && project.hasProperty("precommit")) {
+            // We must exclude kts files from pre-commit hook to prevent detekt from crashing
+            // This is a workaround for the https://github.com/detekt/detekt/issues/5501
+            exclude("*.gradle.kts")
+        }
+    }
+}