Port UnderscoresToCamelCase logic from protobuf java compiler

protoc-gen-kroto-plus/src/main/kotlin/com/github/marcoferrer/krotoplus/utils/StringCaseExts.kt

@@ -18,19 +18,44 @@ package com.github.marcoferrer.krotoplus.utils
 
 import com.google.common.base.CaseFormat
 
+/**
+ * This is the Kotlin implementation of the C++ UnderscoresToCamelCase function that is used by the protobuf java
+ * compiler in the java_helpers.cc file.
+ * See https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/compiler/java/java_helpers.cc#L168-L203
+ * The exact same logic was ported to ensure the generated names match the generated Java names.
+ */
 val upperCamelCase = { it: String ->
-    // We cant use CaseFormat.UPPER_CAMEL since
-    // protoc is lenient with malformed field names
-    if (it.contains("_"))
-        it.split("_").joinToString(separator = "") { it.capitalize() } else
-        it.capitalize()
-
+    StringBuilder().apply {
+        var capNextLetter = true
+        it.forEach { c ->
+            when (c) {
+                in 'a'..'z' -> {
+                    if (capNextLetter) {
+                        append(c.toUpperCase())
+                    } else {
+                        append(c)
+                    }
+                    capNextLetter = false
+                }
+                in 'A'..'Z' -> {
+                    append(c)
+                    capNextLetter = false
+                }
+                in '0'..'9' -> {
+                    append(c)
+                    capNextLetter = true
+                }
+                else -> {
+                    capNextLetter = true
+                }
+            }
+        }
+    }.toString()
 }.memoize()
 
 fun String.toUpperCamelCase(): String = upperCamelCase(this)
 
 private val upperSnakeCase = { it: String ->
-
     val valueCamel = it.toUpperCamelCase()
     CaseFormat.UPPER_CAMEL
         .converterTo(CaseFormat.UPPER_UNDERSCORE)

protoc-gen-kroto-plus/src/test/kotlin/StringCaseExtsTests.kt

@@ -0,0 +1,25 @@
+package com.github.marcoferrer.krotoplus.utils
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class StringCaseExtsTests {
+    @Test
+    fun `toUpperCamelCase capitalizes first character`() {
+        assertEquals("SomethingAwesome", "somethingAwesome".toUpperCamelCase())
+        assertEquals("Test", "test".toUpperCamelCase())
+    }
+
+    @Test
+    fun `toUpperCamelCase uppercases character after underscore`() {
+        assertEquals("ThisIsAnAwesomeText", "this_is_an_awesome_text".toUpperCamelCase())
+        assertEquals("SomeExample", "some_example".toUpperCamelCase())
+    }
+
+    @Test
+    fun `toUpperCamelCase uppercases character after number`() {
+        assertEquals("SomeMethod4Me", "some_method4me".toUpperCamelCase())
+        assertEquals("SomeB2BCase", "some_b2b_case".toUpperCamelCase())
+        assertEquals("Fun4Devs", "fun4devs".toUpperCamelCase())
+    }
+}