Don't generate empty snapshots with config-cache reuse

With configuration-cache enabled, no dependencies will be resolved when
the configuration is loaded from the cache. In this case, we avoid generating
a dependency graph snapshot so that we don't incorrectly report an empty graph.

Fixes #96
Fixes #98

Author: bigdaz

plugin-test/src/test/groovy/org/gradle/github/dependencygraph/BaseExtractorTest.groovy

@@ -6,7 +6,6 @@ import com.networknt.schema.*
 import groovy.json.JsonSlurper
 import groovy.transform.CompileDynamic
 import groovy.transform.CompileStatic
-import groovy.transform.Memoized
 import org.gradle.github.dependencygraph.fixture.TestConfig
 import org.gradle.internal.hash.Hashing
 import org.gradle.test.fixtures.SimpleGradleExecuter
@@ -49,11 +48,14 @@ abstract class BaseExtractorTest extends Specification {
 
     SimpleGradleExecuter createExecuter() {
         // Create a new JsonManifestLoader for each invocation of the executer
-        File manifestFile = reportDir.file("dummy-job-correlator.json")
-        loader = new JsonRepositorySnapshotLoader(manifestFile)
+        loader = new JsonRepositorySnapshotLoader(dependencyGraphFile)
         return createExecuter(testGradleVersion)
     }
 
+    File getDependencyGraphFile() {
+        reportDir.file("dummy-job-correlator.json")
+    }
+
     static String getTestGradleVersion() {
         return System.getProperty("testGradleVersion", GradleVersion.current().version)
     }
@@ -219,20 +221,20 @@ abstract class BaseExtractorTest extends Specification {
     @CompileStatic
     protected static class JsonRepositorySnapshotLoader {
         private static final String SCHEMA = "schema/github-repository-snapshot-schema.json"
-        private final File manifestFile
+        private final File dependencyGraphFile
 
-        JsonRepositorySnapshotLoader(File manifestFile) {
-            this.manifestFile = manifestFile
+        JsonRepositorySnapshotLoader(File dependencyGraphFile) {
+            this.dependencyGraphFile = dependencyGraphFile
         }
 
         protected Map jsonRepositorySnapshot() {
             def jsonSlurper = new JsonSlurper()
-            println(manifestFile.text)
+            println(dependencyGraphFile.text)
             JsonSchema schema = createSchemaValidator()
             ObjectMapper mapper = new ObjectMapper()
-            JsonNode node = mapper.readTree(manifestFile)
+            JsonNode node = mapper.readTree(dependencyGraphFile)
             validateAgainstJsonSchema(schema, node)
-            return jsonSlurper.parse(manifestFile) as Map
+            return jsonSlurper.parse(dependencyGraphFile) as Map
         }
 
         private static void validateAgainstJsonSchema(JsonSchema schema, JsonNode json) {

plugin-test/src/test/groovy/org/gradle/github/dependencygraph/DependencyExtractorConfigTest.groovy

@@ -76,6 +76,16 @@ class DependencyExtractorConfigTest extends BaseExtractorTest {
         manifest.assertResolved([
             "org.test:foo:1.0": [package_url: purlFor(foo)]
         ])
+
+        // Execute again to test loading from config-cache
+        when:
+        dependencyGraphFile.delete()
+        executer.withArgument("--configuration-cache")
+        def buildResult = run()
+
+        then:
+        buildResult.output.contains("Gradle build state was reused from the configuration-cache: Dependency Graph file will not be generated.")
+        !dependencyGraphFile.exists()
     }
 
     def "fails gracefully if configuration values not set"() {

plugin/src/main/kotlin/org/gradle/dependencygraph/extractor/DependencyExtractor.kt

@@ -29,6 +29,8 @@ abstract class DependencyExtractor :
 
     private val pluginParameters = PluginParameters()
 
+    private var settingsEvaluated = false
+
     private val resolvedConfigurations = Collections.synchronizedList(mutableListOf<ResolvedConfiguration>())
 
     private val thrownExceptions = Collections.synchronizedList(mutableListOf<Throwable>())
@@ -112,6 +114,7 @@ abstract class DependencyExtractor :
     open fun extractSettings(
         details: EvaluateSettingsBuildOperationType.Details
     ) {
+        settingsEvaluated = true
         val settingsFile = details.settingsFile
         if (settingsFile != null) {
             buildLayout.addSettings(details.buildPath, settingsFile)
@@ -296,6 +299,15 @@ abstract class DependencyExtractor :
                 thrownExceptions
             )
         }
+
+        // We use the absence of Settings Evaluated to determine if the build was loaded from the configuration-cache
+        if (!settingsEvaluated) {
+            LOGGER.lifecycle(
+                "Gradle build state was reused from the configuration-cache: " +
+                    "Dependency Graph file will not be generated."
+            )
+            return
+        }
         try {
             writeDependencyGraph()
         } catch (e: RuntimeException) {