From a91b813e43c01606d6ba5c01353adea6a1fe417d Mon Sep 17 00:00:00 2001
From: david-perez <d@vidp.dev>
Date: Fri, 17 Jun 2022 18:12:56 +0200
Subject: [PATCH] Fix `modifyMtime` task when `generateSmithyBuild` task is up
 to date (#1471)

When `generateSmithyBuild` task is up to date, the hashes of the build
are not calculated, so `modifyMtime` fails, because it expects them to
be registered in Gradle's project properties. This can happen if you run
a command like `./gradlew codegen-server-test:test` twice consecutively.

In this case, we should skip the `modifyMtime` task altogether.
Everything is up to date, so no codegen will run, and no artifacts will
change.
---
 buildSrc/src/main/kotlin/CodegenTestCommon.kt | 32 +++++++++++--------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/buildSrc/src/main/kotlin/CodegenTestCommon.kt b/buildSrc/src/main/kotlin/CodegenTestCommon.kt
index aa187751a..74b9b313a 100644
--- a/buildSrc/src/main/kotlin/CodegenTestCommon.kt
+++ b/buildSrc/src/main/kotlin/CodegenTestCommon.kt
@@ -130,7 +130,7 @@ fun Project.registerGenerateSmithyBuildTask(
 
             // If this is a rebuild, cache all the hashes of the generated Rust files. These are later used by the
             // `modifyMtime` task.
-            project.extra["previousBuildHashes"] = project.buildDir.walk()
+            project.extra[previousBuildHashesKey] = project.buildDir.walk()
                 .filter { it.isFile }
                 .map {
                     getChecksumForFile(it) to it.lastModified()
@@ -174,6 +174,8 @@ fun Project.registerGenerateCargoConfigTomlTask(
     }
 }
 
+const val previousBuildHashesKey = "previousBuildHashes"
+
 fun Project.registerModifyMtimeTask() {
     // Cargo uses `mtime` (among other factors) to determine whether a compilation unit needs a rebuild. While developing,
     // it is likely that only a small number of the generated crate files are modified across rebuilds. This task compares
@@ -187,19 +189,23 @@ fun Project.registerModifyMtimeTask() {
         dependsOn("generateSmithyBuild")
 
         doFirst {
-            @Suppress("UNCHECKED_CAST") val previousBuildHashes: Map<String, Long> = project.extra["previousBuildHashes"] as Map<String, Long>
-
-            project.buildDir.walk()
-                .filter { it.isFile }
-                .map {
-                    getChecksumForFile(it) to it
-                }
-                .forEach { (currentHash, currentFile) ->
-                    previousBuildHashes[currentHash]?.also { oldMtime ->
-                        println("Setting `mtime` of $currentFile back to `$oldMtime` because its hash `$currentHash` remained unchanged after a rebuild.")
-                        currentFile.setLastModified(oldMtime)
+            if (!project.extra.has(previousBuildHashesKey)) {
+                println("No hashes from a previous build exist because `generateSmithyBuild` is up to date, skipping `mtime` fixups")
+            } else {
+                @Suppress("UNCHECKED_CAST") val previousBuildHashes: Map<String, Long> = project.extra[previousBuildHashesKey] as Map<String, Long>
+
+                project.buildDir.walk()
+                    .filter { it.isFile }
+                    .map {
+                        getChecksumForFile(it) to it
                     }
-                }
+                    .forEach { (currentHash, currentFile) ->
+                        previousBuildHashes[currentHash]?.also { oldMtime ->
+                            println("Setting `mtime` of $currentFile back to `$oldMtime` because its hash `$currentHash` remained unchanged after a rebuild.")
+                            currentFile.setLastModified(oldMtime)
+                        }
+                    }
+            }
         }
     }
 }
-- 
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