Allow passing multiple hashes to the why task (#916)

The `--hash` argument of the `why` task now accepts multiple, comma-separated hashes.

README.md

@@ -160,6 +160,9 @@ This is effectively just a more concise version of `dependencyInsight`:
 ./gradlew  dependencyInsight --configuration unifiedClasspath --dependency jackson-databind
 ```
 
+You can check multiple dependencies at once by passing multiple comma-delimited hash values, e.g.
+`./gradlew why --hash a60c3ce8,400d4d2a`.
+
 ## ./gradlew checkUnusedConstraints
 `checkUnusedConstraints` prevents unnecessary constraints from accruing in your `versions.props` file. Run
 `./gradlew checkUnusedConstraints --fix` to automatically remove any unused constraints from your props file.

changelog/@unreleased/pr-916.v2.yml

@@ -0,0 +1,6 @@
+type: improvement
+improvement:
+  description: The `--hash` argument of the `why` task now accepts multiple, comma-separated
+    hashes.
+  links:
+  - https://github.com/palantir/gradle-consistent-versions/pull/916

src/main/java/com/palantir/gradle/versions/WhyDependencyTask.java

@@ -16,6 +16,7 @@
 
 package com.palantir.gradle.versions;
 
+import com.google.common.base.Splitter;
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Multimaps;
@@ -25,8 +26,10 @@
 import com.palantir.gradle.versions.lockstate.Line;
 import com.palantir.gradle.versions.lockstate.LockStates;
 import java.nio.file.Path;
+import java.util.LinkedHashSet;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Stream;
 import org.gradle.api.DefaultTask;
@@ -78,23 +81,27 @@ public final void taskAction() {
                     "./gradlew why requires a '--hash <hash>' from versions.lock" + example.orElse(""));
         }
 
-        lineByHash.get(hashOption.get()).forEach(line -> {
-            ModuleVersionIdentifier key = MyModuleVersionIdentifier.of(line.group(), line.name(), line.version());
+        Set<String> hashes = new LinkedHashSet<>(Splitter.on(",").splitToList(hashOption.get()));
 
-            Optional<Dependents> entry = Stream.of(
-                            fullLockState.get().productionDeps(),
-                            fullLockState.get().testDeps())
-                    .map(state -> state.get(key))
-                    .filter(Objects::nonNull)
-                    .findFirst();
-            Dependents dependents =
-                    entry.orElseThrow(() -> new NullPointerException("Unable to find group/name in fullLockState"));
+        for (String hash : hashes) {
+            lineByHash.get(hash).forEach(line -> {
+                ModuleVersionIdentifier key = MyModuleVersionIdentifier.of(line.group(), line.name(), line.version());
+
+                Optional<Dependents> entry = Stream.of(
+                                fullLockState.get().productionDeps(),
+                                fullLockState.get().testDeps())
+                        .map(state -> state.get(key))
+                        .filter(Objects::nonNull)
+                        .findFirst();
+                Dependents dependents =
+                        entry.orElseThrow(() -> new NullPointerException("Unable to find group/name in fullLockState"));
 
-            getLogger().lifecycle("{}", key);
-            LockStates.prettyPrintConstraints(dependents).forEach(pretty -> {
-                getLogger().lifecycle("\t{}", pretty);
+                getLogger().lifecycle("{}", key);
+                LockStates.prettyPrintConstraints(dependents).forEach(pretty -> {
+                    getLogger().lifecycle("\t{}", pretty);
+                });
+                getLogger().lifecycle("");
             });
-            getLogger().lifecycle("");
-        });
+        }
     }
 }

src/test/groovy/com/palantir/gradle/versions/VersionsLockPluginIntegrationSpec.groovy

@@ -40,7 +40,9 @@ class VersionsLockPluginIntegrationSpec extends IntegrationSpec {
                 "org.slf4j:slf4j-api:1.7.24",
                 "org.slf4j:slf4j-api:1.7.25",
                 "junit:junit:4.10",
-                "org:test-dep-that-logs:1.0 -> org.slf4j:slf4j-api:1.7.11"
+                "org:test-dep-that-logs:1.0 -> org.slf4j:slf4j-api:1.7.11",
+                "org:another-transitive-dependency:3.2.1",
+                "org:another-direct-dependency:1.2.3 -> org:another-transitive-dependency:3.2.1",
         )
         makePlatformPom(mavenRepo, "org", "platform", "1.0")
 
@@ -534,6 +536,32 @@ class VersionsLockPluginIntegrationSpec extends IntegrationSpec {
         gradleVersionNumber << GRADLE_VERSIONS
     }
 
+    def "#gradleVersionNumber: why with comma-delimited multiple hashes works"() {
+        setup:
+        gradleVersion = gradleVersionNumber
+
+        buildFile << '''
+            apply plugin: 'java'
+            dependencies {
+                implementation 'ch.qos.logback:logback-classic:1.2.3' // brings in slf4j-api 1.7.25
+                implementation 'org:another-direct-dependency:1.2.3' // brings in org:another-transitive-dependency:3.2.1
+            }
+        '''.stripIndent()
+
+        when:
+        runTasks('--write-locks')
+
+        then:
+        def result = runTasks('why', '--hash', '400d4d2a,050d6518') // both transitive dependencies
+        result.output.contains('org.slf4j:slf4j-api:1.7.25')
+        result.output.contains('ch.qos.logback:logback-classic -> 1.7.25')
+        result.output.contains('org:another-transitive-dependency:3.2.1')
+        result.output.contains('org:another-direct-dependency -> 3.2.1')
+
+        where:
+        gradleVersionNumber << GRADLE_VERSIONS
+    }
+
     def '#gradleVersionNumber: does not fail if subproject evaluated later applies base plugin in own build file'() {
         setup:
         gradleVersion = gradleVersionNumber