From d4ab2106edddef33cfdc4b784661f0a4c91ee69a Mon Sep 17 00:00:00 2001
From: Ned Twigg <ned.twigg@diffplug.com>
Date: Wed, 20 Dec 2023 08:57:09 -0800
Subject: [PATCH] Before writing a value, double-check that we can roundtrip
 it.

---
 .../kotlin/com/diffplug/selfie/SourceFile.kt  | 19 +++++++++++++++++++
 .../junit5/__snapshots__/UT_PrismTrainTest.ss |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/SourceFile.kt b/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/SourceFile.kt
index 94af2c17..3b84a3e5 100644
--- a/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/SourceFile.kt
+++ b/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/SourceFile.kt
@@ -43,6 +43,25 @@ class SourceFile(filename: String, content: String) {
      */
     fun <T : Any> setLiteralAndGetNewlineDelta(literalValue: LiteralValue<T>): Int {
       val encoded = literalValue.format.encode(literalValue.actual, language)
+      val roundTripped = literalValue.format.parse(encoded, language) // sanity check
+      if (roundTripped != literalValue.actual) {
+        throw Error(
+            "There is an error in " +
+                literalValue.format::class.simpleName +
+                ", the following value isn't roundtripping.\n" +
+                "Please this error and the data below at https://github.com/diffplug/selfie/issues/new\n" +
+                "```\n" +
+                "ORIGINAL\n" +
+                literalValue.actual +
+                "\n" +
+                "ROUNDTRIPPED\n" +
+                roundTripped +
+                "\n" +
+                "ENCODED ORIGINAL\n" +
+                encoded +
+                "\n" +
+                "```\n")
+      }
       val existingNewlines = slice.count { it == '\n' }
       val newNewlines = encoded.count { it == '\n' }
       contentSlice = Slice(slice.replaceSelfWith(".toBe($encoded)"))
diff --git a/undertest-junit5/src/test/kotlin/undertest/junit5/__snapshots__/UT_PrismTrainTest.ss b/undertest-junit5/src/test/kotlin/undertest/junit5/__snapshots__/UT_PrismTrainTest.ss
index 67565856..8df13763 100644
--- a/undertest-junit5/src/test/kotlin/undertest/junit5/__snapshots__/UT_PrismTrainTest.ss
+++ b/undertest-junit5/src/test/kotlin/undertest/junit5/__snapshots__/UT_PrismTrainTest.ss
@@ -1,3 +1,5 @@
 ╔═ selfie ═╗
 apple
+╔═ selfie[count] ═╗
+5
 ╔═ [end of file] ═╗