ProfileFileSupplier aggregate files in order (#3754)

* Bug fix: ProfileFileSupplier aggregate files in order

* Update solution to use LinkedHashMap

* Wrap LinkedHashMap into synchronized Map

Author: dave-fn

.changes/next-release/bugfix-AWSSDKforJavav2-6d1d0aa.json

@@ -0,0 +1,6 @@
+{
+    "category": "AWS SDK for Java v2", 
+    "contributor": "", 
+    "type": "bugfix", 
+    "description": "Keep precedence of options when passed to ProfileFileSupplier.aggregate"
+}

core/profiles/src/main/java/software/amazon/awssdk/profiles/ProfileFileSupplier.java

@@ -16,9 +16,11 @@
 package software.amazon.awssdk.profiles;
 
 import java.nio.file.Path;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 import software.amazon.awssdk.annotations.SdkPublicApi;
@@ -119,7 +121,8 @@ static ProfileFileSupplier aggregate(ProfileFileSupplier... suppliers) {
         return new ProfileFileSupplier() {
 
             final AtomicReference<ProfileFile> currentAggregateProfileFile = new AtomicReference<>();
-            final ConcurrentHashMap<Supplier<ProfileFile>, ProfileFile> currentValuesBySupplier = new ConcurrentHashMap<>();
+            final Map<Supplier<ProfileFile>, ProfileFile> currentValuesBySupplier
+                = Collections.synchronizedMap(new LinkedHashMap<>());
 
             @Override
             public ProfileFile get() {

core/profiles/src/test/java/software/amazon/awssdk/profiles/ProfileFileSupplierTest.java

@@ -410,6 +410,56 @@ void aggregate_supplierReturnsSameInstanceMultipleTimesAggregatingProfileFileSup
         assertThat(suppliedProfileFiles).isEqualTo(distinctAggregateProfileFiles);
     }
 
+    @Test
+    void aggregate_duplicateOptionsGivenFixedProfileFirst_preservesPrecedence() {
+        ProfileFile configFile1 = configFile("profile default", Pair.of("aws_access_key_id", "config-key"));
+        Path credentialsFilePath = generateTestCredentialsFile("defaultAccessKey", "defaultSecretAccessKey");
+
+        ProfileFileSupplier supplier = ProfileFileSupplier.aggregate(
+            ProfileFileSupplier.fixedProfileFile(configFile1),
+            ProfileFileSupplier.reloadWhenModified(credentialsFilePath, ProfileFile.Type.CREDENTIALS));
+
+        ProfileFile profileFile = supplier.get();
+        String accessKeyId = profileFile.profile("default").get().property("aws_access_key_id").get();
+
+        assertThat(accessKeyId).isEqualTo("config-key");
+
+        generateTestCredentialsFile("defaultAccessKey2", "defaultSecretAccessKey2");
+
+        profileFile = supplier.get();
+        accessKeyId = profileFile.profile("default").get().property("aws_access_key_id").get();
+
+        assertThat(accessKeyId).isEqualTo("config-key");
+    }
+
+    @Test
+    void aggregate_duplicateOptionsGivenReloadingProfileFirst_preservesPrecedence() {
+        AdjustableClock clock = new AdjustableClock();
+
+        ProfileFile configFile1 = configFile("profile default", Pair.of("aws_access_key_id", "config-key"));
+        Path credentialsFilePath = generateTestCredentialsFile("defaultAccessKey", "defaultSecretAccessKey");
+
+        ProfileFileSupplier supplier = ProfileFileSupplier.aggregate(
+            builderWithClock(clock)
+                .reloadWhenModified(credentialsFilePath, ProfileFile.Type.CREDENTIALS)
+                .build(),
+            ProfileFileSupplier.fixedProfileFile(configFile1));
+
+        ProfileFile profileFile = supplier.get();
+        String accessKeyId = profileFile.profile("default").get().property("aws_access_key_id").get();
+
+        assertThat(accessKeyId).isEqualTo("defaultAccessKey");
+
+        generateTestCredentialsFile("defaultAccessKey2", "defaultSecretAccessKey2");
+
+        clock.tickForward(Duration.ofMillis(1_000));
+
+        profileFile = supplier.get();
+        accessKeyId = profileFile.profile("default").get().property("aws_access_key_id").get();
+
+        assertThat(accessKeyId).isEqualTo("defaultAccessKey2");
+    }
+
     @Test
     void fixedProfileFile_nullProfileFile_returnsNonNullSupplier() {
         ProfileFile file = null;