Ignore unresolvable placeholder in log properties

Update the RelaxedPropertyResolver used to load log properties so that
`${...}` patterns are ignored when possible.

Fixes gh-7719

spring-boot/src/main/java/org/springframework/boot/bind/RelaxedPropertyResolver.java

@@ -19,7 +19,9 @@ package org.springframework.boot.bind;
 import java.util.Map;
 
 import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.Environment;
 import org.springframework.core.env.PropertyResolver;
+import org.springframework.core.env.PropertySourcesPropertyResolver;
 import org.springframework.util.Assert;
 
 /**
@@ -145,4 +147,25 @@ public class RelaxedPropertyResolver implements PropertyResolver {
 				keyPrefix);
 	}
 
+	/**
+	 * Return a property resolver for the environment, preferring one that ignores
+	 * unresolvable nested placeholders.
+	 * @param environment the source environment
+	 * @param prefix the prefix
+	 * @return a property resolver for the environment
+	 * @since 1.4.3
+	 */
+	public static RelaxedPropertyResolver ignoringUnresolvableNestedPlaceholders(
+			Environment environment, String prefix) {
+		Assert.notNull(environment, "Environment must not be null");
+		PropertyResolver resolver = environment;
+		if (environment instanceof ConfigurableEnvironment) {
+			resolver = new PropertySourcesPropertyResolver(
+					((ConfigurableEnvironment) environment).getPropertySources());
+			((PropertySourcesPropertyResolver) resolver)
+					.setIgnoreUnresolvableNestedPlaceholders(true);
+		}
+		return new RelaxedPropertyResolver(resolver, prefix);
+	}
+
 }

spring-boot/src/main/java/org/springframework/boot/logging/LoggingSystemProperties.java

@@ -49,8 +49,8 @@ class LoggingSystemProperties {
 	}
 
 	public void apply(LogFile logFile) {
-		RelaxedPropertyResolver propertyResolver = new RelaxedPropertyResolver(
-				this.environment, "logging.");
+		RelaxedPropertyResolver propertyResolver = RelaxedPropertyResolver
+				.ignoringUnresolvableNestedPlaceholders(this.environment, "logging.");
 		setSystemProperty(propertyResolver, EXCEPTION_CONVERSION_WORD,
 				"exception-conversion-word");
 		setSystemProperty(propertyResolver, CONSOLE_LOG_PATTERN, "pattern.console");

spring-boot/src/main/java/org/springframework/boot/logging/logback/DefaultLogbackConfiguration.java

@@ -72,7 +72,8 @@ class DefaultLogbackConfiguration {
 		if (environment == null) {
 			return new PropertySourcesPropertyResolver(null);
 		}
-		return new RelaxedPropertyResolver(environment, "logging.pattern.");
+		return RelaxedPropertyResolver.ignoringUnresolvableNestedPlaceholders(environment,
+				"logging.pattern.");
 	}
 
 	public void apply(LogbackConfigurator config) {

spring-boot/src/test/java/org/springframework/boot/logging/LoggingApplicationListenerTests.java

@@ -467,6 +467,16 @@ public class LoggingApplicationListenerTests {
 		assertThat(System.getProperty("PID")).isNotNull();
 	}
 
+	@Test
+	public void environmentPropertiesIgnoreUnresolvablePlaceholders() {
+		// gh-7719
+		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.context,
+				"logging.pattern.console=console ${pid}");
+		this.initializer.initialize(this.context.getEnvironment(),
+				this.context.getClassLoader());
+		assertThat(System.getProperty("CONSOLE_LOG_PATTERN")).isEqualTo("console ${pid}");
+	}
+
 	@Test
 	public void logFilePropertiesCanReferenceSystemProperties() {
 		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(this.context,