Add baseline functionality to ktlint

README.md

@@ -168,6 +168,9 @@ $ ktlint --reporter=plain?group_by_file
 # print style violations as usual + create report in checkstyle format 
 $ ktlint --reporter=plain --reporter=checkstyle,output=ktlint-report-in-checkstyle-format.xml
 
+# check against a baseline file
+$ ktlint --baseline=ktlint-baseline.xml
+
 # install git hook to automatically check files for style violations on commit
 # Run "ktlint installGitPrePushHook" if you wish to run ktlint on push instead
 $ ktlint installGitPreCommitHook
@@ -288,6 +291,8 @@ task ktlint(type: JavaExec, group: "verification") {
     args "src/**/*.kt"
     // to generate report in checkstyle format prepend following args:
     // "--reporter=plain", "--reporter=checkstyle,output=${buildDir}/ktlint.xml"
+    // to add a baseline to check against prepend following args:
+    // "--baseline=ktlint-baseline.xml"
     // see https://github.com/pinterest/ktlint#usage for more
 }
 check.dependsOn ktlint

build.gradle

@@ -42,7 +42,7 @@ task ktlint(type: JavaExec, group: LifecycleBasePlugin.VERIFICATION_GROUP) {
   description = "Check Kotlin code style."
   classpath = configurations.ktlint
   main = 'com.pinterest.ktlint.Main'
-  args '*/src/**/*.kt'
+  args '*/src/**/*.kt', '--baseline=ktlint-baseline.xml'
 }
 
 allprojects {

ktlint-baseline.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<baseline version="1.0">
+	<file name="ktlint/src/test/resources/TestBaselineExtraErrorFile.kt">
+		<error line="1" column="34" source="no-empty-class-body" />
+		<error line="2" column="1" source="no-blank-line-before-rbrace" />
+	</file>
+	<file name="ktlint/src/test/resources/TestBaselineFile.kt">
+		<error line="1" column="24" source="no-empty-class-body" />
+		<error line="2" column="1" source="no-blank-line-before-rbrace" />
+	</file>
+</baseline>

ktlint-reporter-baseline/build.gradle

@@ -0,0 +1,12 @@
+plugins {
+  id 'org.jetbrains.kotlin.jvm'
+  id 'ktlint-publication'
+}
+
+dependencies {
+  implementation project(':ktlint-core')
+  implementation deps.kotlin.stdlib
+
+  testImplementation deps.junit
+  testImplementation deps.assertj
+}

ktlint-reporter-baseline/gradle.properties

@@ -0,0 +1,4 @@
+GROUP=com.pinterest.ktlint
+POM_NAME=ktlint-reporter-baseline
+POM_ARTIFACT_ID=ktlint-reporter-baseline
+POM_PACKAGING=jar

ktlint-reporter-baseline/src/main/kotlin/com/pinterest/ktlint/reporter/baseline/BaselineReporter.kt

@@ -0,0 +1,46 @@
+package com.pinterest.ktlint.reporter.baseline
+
+import com.pinterest.ktlint.core.LintError
+import com.pinterest.ktlint.core.Reporter
+import java.io.File
+import java.io.PrintStream
+import java.nio.file.Paths
+import java.util.ArrayList
+import java.util.concurrent.ConcurrentHashMap
+
+class BaselineReporter(val out: PrintStream) : Reporter {
+
+    private val acc = ConcurrentHashMap<String, MutableList<LintError>>()
+
+    override fun onLintError(file: String, err: LintError, corrected: Boolean) {
+        if (!corrected) {
+            acc.getOrPut(file) { ArrayList<LintError>() }.add(err)
+        }
+    }
+
+    override fun afterAll() {
+        out.println("""<?xml version="1.0" encoding="utf-8"?>""")
+        out.println("""<baseline version="1.0">""")
+        for ((file, errList) in acc.entries.sortedBy { it.key }) {
+            val fileName = try {
+                val rootPath = Paths.get("").toAbsolutePath()
+                val filePath = Paths.get(file)
+                rootPath.relativize(filePath).toString().replace(File.separatorChar, '/')
+            } catch (e: IllegalArgumentException) {
+                file
+            }
+            out.println("""	<file name="${fileName.escapeXMLAttrValue()}">""")
+            for ((line, col, ruleId, _) in errList) {
+                out.println(
+                    """		<error line="$line" column="$col" source="$ruleId" />"""
+                )
+            }
+            out.println("""	</file>""")
+        }
+        out.println("""</baseline>""")
+    }
+
+    private fun String.escapeXMLAttrValue() =
+        this.replace("&", "&amp;").replace("\"", "&quot;").replace("'", "&apos;")
+            .replace("<", "&lt;").replace(">", "&gt;")
+}

ktlint-reporter-baseline/src/main/kotlin/com/pinterest/ktlint/reporter/baseline/BaselineReporterProvider.kt

@@ -0,0 +1,10 @@
+package com.pinterest.ktlint.reporter.baseline
+
+import com.pinterest.ktlint.core.Reporter
+import com.pinterest.ktlint.core.ReporterProvider
+import java.io.PrintStream
+
+class BaselineReporterProvider : ReporterProvider {
+    override val id: String = "baseline"
+    override fun get(out: PrintStream, opt: Map<String, String>): Reporter = BaselineReporter(out)
+}

ktlint-reporter-baseline/src/main/resources/META-INF/services/com.pinterest.ktlint.core.ReporterProvider

@@ -0,0 +1 @@
+com.pinterest.ktlint.reporter.baseline.BaselineReporterProvider

ktlint-reporter-baseline/src/test/kotlin/com/pinterest/ktlint/reporter/baseline/BaselineReporterTest.kt

@@ -0,0 +1,75 @@
+package com.pinterest.ktlint.reporter.baseline
+
+import com.pinterest.ktlint.core.LintError
+import java.io.ByteArrayOutputStream
+import java.io.PrintStream
+import java.nio.file.Paths
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+
+class BaselineReporterTest {
+
+    @Test
+    fun testReportGeneration() {
+        val basePath = Paths.get("").toAbsolutePath()
+        val out = ByteArrayOutputStream()
+        val reporter = BaselineReporter(PrintStream(out, true))
+        reporter.onLintError(
+            "$basePath/one-fixed-and-one-not.kt",
+            LintError(
+                1, 1, "rule-1",
+                "<\"&'>"
+            ),
+            false
+        )
+        reporter.onLintError(
+            "$basePath/one-fixed-and-one-not.kt",
+            LintError(
+                2, 1, "rule-2",
+                "And if you see my friend"
+            ),
+            true
+        )
+
+        reporter.onLintError(
+            "$basePath/two-not-fixed.kt",
+            LintError(
+                1, 10, "rule-1",
+                "I thought I would again"
+            ),
+            false
+        )
+        reporter.onLintError(
+            "$basePath/two-not-fixed.kt",
+            LintError(
+                2, 20, "rule-2",
+                "A single thin straight line"
+            ),
+            false
+        )
+
+        reporter.onLintError(
+            "$basePath/all-corrected.kt",
+            LintError(
+                1, 1, "rule-1",
+                "I thought we had more time"
+            ),
+            true
+        )
+        reporter.afterAll()
+        assertThat(String(out.toByteArray())).isEqualTo(
+"""
+<?xml version="1.0" encoding="utf-8"?>
+<baseline version="1.0">
+	<file name="one-fixed-and-one-not.kt">
+		<error line="1" column="1" source="rule-1" />
+	</file>
+	<file name="two-not-fixed.kt">
+		<error line="1" column="10" source="rule-1" />
+		<error line="2" column="20" source="rule-2" />
+	</file>
+</baseline>
+""".trimStart().replace("\n", System.lineSeparator())
+        )
+    }
+}

ktlint/build.gradle

@@ -25,6 +25,7 @@ publishing.publications.named("maven").configure {
 
 dependencies {
   implementation project(':ktlint-core')
+  implementation project(':ktlint-reporter-baseline')
   implementation project(':ktlint-reporter-checkstyle')
   implementation project(':ktlint-reporter-json')
   implementation project(':ktlint-reporter-html')

ktlint/src/main/kotlin/com/pinterest/ktlint/Main.kt

@@ -17,12 +17,15 @@ import com.pinterest.ktlint.internal.GitPrePushHookSubCommand
 import com.pinterest.ktlint.internal.JarFiles
 import com.pinterest.ktlint.internal.KtlintVersionProvider
 import com.pinterest.ktlint.internal.PrintASTSubCommand
+import com.pinterest.ktlint.internal.containsLintError
 import com.pinterest.ktlint.internal.fileSequence
 import com.pinterest.ktlint.internal.formatFile
 import com.pinterest.ktlint.internal.lintFile
+import com.pinterest.ktlint.internal.loadBaseline
 import com.pinterest.ktlint.internal.loadRulesets
 import com.pinterest.ktlint.internal.location
 import com.pinterest.ktlint.internal.printHelpOrVersionUsage
+import com.pinterest.ktlint.internal.relativeRoute
 import com.pinterest.ktlint.internal.toFilesURIList
 import com.pinterest.ktlint.reporter.plain.internal.Color
 import java.io.File
@@ -212,6 +215,12 @@ class KtlintCommandLine {
     )
     var experimental: Boolean = false
 
+    @Option(
+        names = ["--baseline"],
+        description = ["Defines a baseline file to check against"]
+    )
+    private var baseline: String = ""
+
     @Parameters(hidden = true)
     private var patterns = ArrayList<String>()
 
@@ -224,8 +233,14 @@ class KtlintCommandLine {
 
         val start = System.currentTimeMillis()
 
+        val baselineResults = loadBaseline(baseline)
         val ruleSetProviders = rulesets.loadRulesets(experimental, debug)
-        val reporter = loadReporter()
+        var reporter = loadReporter()
+        if (baselineResults.baselineGenerationNeeded) {
+            val baselineReporter = ReporterTemplate("baseline", null, emptyMap(), baseline)
+            val reporterProviderById = loadReporters(emptyList())
+            reporter = Reporter.from(reporter, baselineReporter.toReporter(reporterProviderById))
+        }
         val userData = listOfNotNull(
             "android" to android.toString(),
             if (disabledRules.isNotBlank()) "disabled_rules" to disabledRules else null
@@ -235,7 +250,7 @@ class KtlintCommandLine {
         if (stdin) {
             lintStdin(ruleSetProviders, userData, reporter)
         } else {
-            lintFiles(ruleSetProviders, userData, reporter)
+            lintFiles(ruleSetProviders, userData, baselineResults.baselineRules, reporter)
         }
         reporter.afterAll()
         if (debug) {
@@ -253,6 +268,7 @@ class KtlintCommandLine {
     private fun lintFiles(
         ruleSetProviders: Map<String, RuleSetProvider>,
         userData: Map<String, String>,
+        baseline: Map<String, List<LintError>>?,
         reporter: Reporter
     ) {
         patterns.fileSequence()
@@ -263,7 +279,8 @@ class KtlintCommandLine {
                         file.path,
                         file.readText(),
                         ruleSetProviders,
-                        userData
+                        userData,
+                        baseline?.get(file.relativeRoute)
                     )
                 }
             }
@@ -281,7 +298,8 @@ class KtlintCommandLine {
                 KtLint.STDIN_FILE,
                 String(System.`in`.readBytes()),
                 ruleSetProviders,
-                userData
+                userData,
+                null
             ),
             reporter
         )
@@ -324,7 +342,8 @@ class KtlintCommandLine {
         fileName: String,
         fileContent: String,
         ruleSetProviders: Map<String, RuleSetProvider>,
-        userData: Map<String, String>
+        userData: Map<String, String>,
+        baselineErrors: List<LintError>?
     ): List<LintErrorWithCorrectionInfo> {
         if (debug) {
             val fileLocation = if (fileName != KtLint.STDIN_FILE) File(fileName).location(relative) else fileName
@@ -342,8 +361,10 @@ class KtlintCommandLine {
                     debug
                 ) { err, corrected ->
                     if (!corrected) {
-                        result.add(LintErrorWithCorrectionInfo(err, corrected))
-                        tripped.set(true)
+                        if (baselineErrors == null || !baselineErrors.containsLintError(err)) {
+                            result.add(LintErrorWithCorrectionInfo(err, corrected))
+                            tripped.set(true)
+                        }
                     }
                 }
             } catch (e: Exception) {
@@ -368,8 +389,10 @@ class KtlintCommandLine {
                     editorConfigPath,
                     debug
                 ) { err ->
-                    result.add(LintErrorWithCorrectionInfo(err, false))
-                    tripped.set(true)
+                    if (baselineErrors == null || !baselineErrors.containsLintError(err)) {
+                        result.add(LintErrorWithCorrectionInfo(err, false))
+                        tripped.set(true)
+                    }
                 }
             } catch (e: Exception) {
                 result.add(LintErrorWithCorrectionInfo(e.toLintError(), false))