Adds support for non-enumerable property sources in bootstrap.

Fixes gh-724

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/config/BootstrapPropertySource.java

@@ -27,13 +27,15 @@ import org.springframework.util.StringUtils;
 import static org.springframework.cloud.bootstrap.config.PropertySourceBootstrapConfiguration.BOOTSTRAP_PROPERTY_SOURCE_NAME;
 
 /**
+ * Enumerable wrapper for a property source.
+ *
  * @author Ryan Baxter
  */
 public class BootstrapPropertySource<T> extends EnumerablePropertySource<T> {
 
-	private PropertySource<T> delegate;
+	private EnumerablePropertySource<T> delegate;
 
-	public BootstrapPropertySource(PropertySource<T> delegate) {
+	public BootstrapPropertySource(EnumerablePropertySource<T> delegate) {
 		super(BOOTSTRAP_PROPERTY_SOURCE_NAME + "-" + delegate.getName(),
 				delegate.getSource());
 		this.delegate = delegate;
@@ -47,13 +49,7 @@ public class BootstrapPropertySource<T> extends EnumerablePropertySource<T> {
 	@Override
 	public String[] getPropertyNames() {
 		Set<String> names = new LinkedHashSet<>();
-		if (!(this.delegate instanceof EnumerablePropertySource)) {
-			throw new IllegalStateException(
-					"Failed to enumerate property names due to non-enumerable property source: "
-							+ this.delegate);
-		}
-		names.addAll(Arrays.asList(
-				((EnumerablePropertySource<?>) this.delegate).getPropertyNames()));
+		names.addAll(Arrays.asList(this.delegate.getPropertyNames()));
 
 		return StringUtils.toStringArray(names);
 	}

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/config/PropertySourceBootstrapConfiguration.java

@@ -45,6 +45,7 @@ import org.springframework.core.Ordered;
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.env.CompositePropertySource;
 import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.EnumerablePropertySource;
 import org.springframework.core.env.Environment;
 import org.springframework.core.env.MutablePropertySources;
 import org.springframework.core.env.PropertySource;
@@ -100,7 +101,13 @@ public class PropertySourceBootstrapConfiguration implements
 			}
 			List<PropertySource<?>> sourceList = new ArrayList<>();
 			for (PropertySource<?> p : source) {
-				sourceList.add(new BootstrapPropertySource<>(p));
+				if (p instanceof EnumerablePropertySource) {
+					EnumerablePropertySource<?> enumerable = (EnumerablePropertySource<?>) p;
+					sourceList.add(new BootstrapPropertySource<>(enumerable));
+				}
+				else {
+					sourceList.add(new SimpleBootstrapPropertySource(p));
+				}
 			}
 			logger.info("Located property source: " + sourceList);
 			composite.addAll(sourceList);

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/config/SimpleBootstrapPropertySource.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2012-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.bootstrap.config;
+
+import org.springframework.core.env.PropertySource;
+
+import static org.springframework.cloud.bootstrap.config.PropertySourceBootstrapConfiguration.BOOTSTRAP_PROPERTY_SOURCE_NAME;
+
+/**
+ * Simple, non-enumerable PropertySource wrapper.
+ * @author Ryan Baxter
+ */
+public class SimpleBootstrapPropertySource<T> extends PropertySource<T> {
+
+	private PropertySource<T> delegate;
+
+	public SimpleBootstrapPropertySource(PropertySource<T> delegate) {
+		super(BOOTSTRAP_PROPERTY_SOURCE_NAME + "-" + delegate.getName(),
+				delegate.getSource());
+		this.delegate = delegate;
+	}
+
+	@Override
+	public Object getProperty(String name) {
+		return this.delegate.getProperty(name);
+	}
+
+	public PropertySource<T> getDelegate() {
+		return delegate;
+	}
+
+}

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/config/BootstrapConfigurationTests.java

@@ -416,12 +416,37 @@ public class BootstrapConfigurationTests {
 				.isEqualTo("Hello added!");
 	}
 
+	@Test
+	public void nonEnumerablePropertySourceWorks() {
+		this.context = new SpringApplicationBuilder().web(WebApplicationType.NONE)
+				.sources(BareConfiguration.class)
+				.properties("spring.cloud.bootstrap.name=nonenumerable").run();
+		then(this.context.getEnvironment().getProperty("foo")).isEqualTo("bar");
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@EnableConfigurationProperties
 	protected static class BareConfiguration {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	// This is added to bootstrap context as a source in bootstrap.properties
+	protected static class SimplePropertySourceConfiguration
+			implements PropertySourceLocator {
+
+		@Override
+		public PropertySource<?> locate(Environment environment) {
+			return new PropertySource("testBootstrapSimple", this) {
+				@Override
+				public Object getProperty(String name) {
+					return ("foo".equals(name)) ? "bar" : null;
+				}
+			};
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@ConfigurationProperties("expected")
 	// This is added to bootstrap context as a source in bootstrap.properties

spring-cloud-context/src/test/resources/nonenumerable.properties

@@ -0,0 +1 @@
+spring.main.sources:org.springframework.cloud.bootstrap.config.BootstrapConfigurationTests.PropertySourceConfiguration,org.springframework.cloud.bootstrap.config.BootstrapConfigurationTests.SimplePropertySourceConfiguration