Escape members that contains only underscores (#1100)

* Escape members that contains only underscores:

`data class(val `____`: String)`

* remove underscore keyword

* fix failed tests

* add allStringsAreEscaped test

* rename test

2 files changed, 48 insertions, 7 deletions

diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/Util.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/Util.kt
index 728f6c4e..d2ba2c7f 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/Util.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/Util.kt
@@ -251,10 +251,14 @@ private val KEYWORDS = setOf(
 
 private const val ALLOWED_CHARACTER = '$'
 
+private const val UNDERSCORE_CHARACTER = '_'
+
 internal val String.isKeyword get() = this in KEYWORDS
 
 internal val String.hasAllowedCharacters get() = this.any { it == ALLOWED_CHARACTER }
 
+internal val String.allCharactersAreUnderscore get() = this.all { it == UNDERSCORE_CHARACTER }
+
 // https://github.com/JetBrains/kotlin/blob/master/compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/JvmSimpleNameBacktickChecker.kt
 private val ILLEGAL_CHARACTERS_TO_ESCAPE = setOf('.', ';', '[', ']', '/', '<', '>', ':', '\\')
 
@@ -265,13 +269,11 @@ private fun String.failIfEscapeInvalid() {
   }
 }
 
-internal fun String.escapeIfNecessary(validate: Boolean = true): String {
-  val escapedString = escapeIfNotJavaIdentifier().escapeIfKeyword().escapeIfHasAllowedCharacters()
-  if (validate) {
-    escapedString.failIfEscapeInvalid()
-  }
-  return escapedString
-}
+internal fun String.escapeIfNecessary(validate: Boolean = true): String = escapeIfNotJavaIdentifier()
+  .escapeIfKeyword()
+  .escapeIfHasAllowedCharacters()
+  .escapeIfAllCharactersAreUnderscore()
+  .apply { if (validate) failIfEscapeInvalid() }
 
 private fun String.alreadyEscaped() = startsWith("`") && endsWith("`")
 
@@ -279,6 +281,8 @@ private fun String.escapeIfKeyword() = if (isKeyword && !alreadyEscaped()) "`$th
 
 private fun String.escapeIfHasAllowedCharacters() = if (hasAllowedCharacters && !alreadyEscaped()) "`$this`" else this
 
+private fun String.escapeIfAllCharactersAreUnderscore() = if (allCharactersAreUnderscore && !alreadyEscaped()) "`$this`" else this
+
 private fun String.escapeIfNotJavaIdentifier(): String {
   return if (!Character.isJavaIdentifierStart(first()) ||
     drop(1).any { !Character.isJavaIdentifierPart(it) } && !alreadyEscaped()
diff --git a/kotlinpoet/src/test/java/com/squareup/kotlinpoet/KotlinPoetTest.kt b/kotlinpoet/src/test/java/com/squareup/kotlinpoet/KotlinPoetTest.kt
index e816d308..be36267c 100644
--- a/kotlinpoet/src/test/java/com/squareup/kotlinpoet/KotlinPoetTest.kt
+++ b/kotlinpoet/src/test/java/com/squareup/kotlinpoet/KotlinPoetTest.kt
@@ -1223,4 +1223,41 @@ class KotlinPoetTest {
       |""".trimMargin()
     )
   }
+
+  @Test fun allStringsAreUnderscore() {
+    val file = FileSpec.builder("com.squareup.tacos", "SourceWithUnderscores")
+      .addType(
+        TypeSpec.classBuilder("SourceWithUnderscores")
+          .primaryConstructor(
+            FunSpec.constructorBuilder()
+              .addParameter("_", Float::class)
+              .addParameter("____", Float::class)
+              .build()
+          )
+          .addProperty(
+            PropertySpec.builder("_", Float::class)
+              .initializer("_")
+              .build()
+          )
+          .addProperty(
+            PropertySpec.builder("____", Float::class)
+              .initializer("____")
+              .build()
+          )
+          .build()
+      )
+      .build()
+    assertThat(file.toString()).isEqualTo(
+      """
+      |package com.squareup.tacos
+      |
+      |import kotlin.Float
+      |
+      |public class SourceWithUnderscores(
+      |  public val `_`: Float,
+      |  public val `____`: Float
+      |)
+      |""".trimMargin()
+    )
+  }
 }