Inform user about using --format option of KtLint CLI

CHANGELOG.md

@@ -32,7 +32,7 @@ At this point in time, it is not yet decided what the next steps will be. Ktlint
 * Add new experimental rule `statement-wrapping` which ensures function, class, or other blocks statement body doesn't start or end at starting or ending braces of the block ([#1938](https://github.com/pinterest/ktlint/issues/1938))
 * Add new experimental rule `blank-line-before-declaration`. This rule requires a blank line before class, function or property declarations ([#1939](https://github.com/pinterest/ktlint/issues/1939))
 * Wrap multiple statements on same line `wrapping` ([#1078](https://github.com/pinterest/ktlint/issues/1078))
-
+* Inform user about using `--format` option of KtLint CLI when finding a violation that can be autocorrected ([#1071](https://github.com/pinterest/ktlint/issues/1071))
 
 ### Removed
 

ktlint-cli/src/main/kotlin/com/pinterest/ktlint/cli/internal/KtlintCommandLine.kt

@@ -242,6 +242,7 @@ internal class KtlintCommandLine {
     private val tripped = AtomicBoolean()
     private val fileNumber = AtomicInteger()
     private val errorNumber = AtomicInteger()
+    private val adviseToUseFormat = AtomicBoolean()
 
     internal var debug: Boolean = false
         get() = Level.DEBUG.isGreaterOrEqual(minLogLevel)
@@ -329,6 +330,13 @@ internal class KtlintCommandLine {
                 baseline.lintErrorsPerFile,
                 aggregatedReporter,
             )
+            if (adviseToUseFormat.get()) {
+                if (format) {
+                    logger.error { "Format was not able to autocorrect all errors that theoretically can be autocorrected." }
+                } else {
+                    logger.warn { "Lint has found errors than can be autocorrected using 'ktlint --format'" }
+                }
+            }
         }
         aggregatedReporter.afterAll()
 
@@ -454,6 +462,9 @@ internal class KtlintCommandLine {
         fileNumber.incrementAndGet()
         val errListLimit = minOf(ktlintCliErrors.size, maxOf(limit - errorNumber.get(), 0))
         errorNumber.addAndGet(errListLimit)
+        if (!adviseToUseFormat.get() && ktlintCliErrors.containsErrorThatCanBeAutocorrected()) {
+            adviseToUseFormat.set(true)
+        }
 
         reporter.before(relativeRoute)
         ktlintCliErrors
@@ -462,6 +473,8 @@ internal class KtlintCommandLine {
         reporter.after(relativeRoute)
     }
 
+    private fun List<KtlintCliError>.containsErrorThatCanBeAutocorrected() = any { it.status == LINT_CAN_BE_AUTOCORRECTED }
+
     private fun process(
         ktLintRuleEngine: KtLintRuleEngine,
         code: Code,

ktlint-cli/src/test/kotlin/com/pinterest/ktlint/cli/SimpleCLITest.kt

@@ -78,6 +78,24 @@ class SimpleCLITest {
             }
     }
 
+    @Test
+    fun `Given some code with an error then return from lint with the error exit code and warning to use --format`(
+        @TempDir
+        tempDir: Path,
+    ) {
+        CommandLineTestRunner(tempDir)
+            .run(
+                "too-many-empty-lines",
+                listOf("**/*.test"),
+            ) {
+                SoftAssertions().apply {
+                    assertErrorExitCode()
+                    assertThat(normalOutput)
+                        .containsLineMatching(Regex(".* WARN .* Lint has found errors than can be autocorrected using 'ktlint --format'"))
+                }.assertAll()
+            }
+    }
+
     @Test
     fun `Given some code with an error but a glob which does not select the file`(
         @TempDir