Derive driverClassName from URL when otherwise unknown

See gh-39376

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jdbc/DataSourceBuilder.java

@@ -186,8 +186,8 @@ public final class DataSourceBuilder<T extends DataSource> {
 		}
 		if (!applied.contains(DataSourceProperty.DRIVER_CLASS_NAME)
 				&& properties.canSet(DataSourceProperty.DRIVER_CLASS_NAME)
-				&& this.values.containsKey(DataSourceProperty.URL)) {
-			String url = this.values.get(DataSourceProperty.URL);
+				&& applied.contains(DataSourceProperty.URL)) {
+			String url = properties.get(dataSource, DataSourceProperty.URL);
 			DatabaseDriver driver = DatabaseDriver.fromJdbcUrl(url);
 			properties.set(dataSource, DataSourceProperty.DRIVER_CLASS_NAME, driver.getDriverClassName());
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jdbc/DataSourceBuilderTests.java

@@ -457,6 +457,20 @@ class DataSourceBuilderTests {
 		assertThat(testSource.getPassword()).isEqualTo("secret");
 	}
 
+	@Test
+	void buildWhenDerivedFromCustomTypeDeriveDriverClassNameFromDerivedUrl() {
+		UrlCapableLimitedCustomDataSource dataSource = new UrlCapableLimitedCustomDataSource();
+		dataSource.setUsername("test");
+		dataSource.setPassword("secret");
+		dataSource.setUrl("jdbc:postgresql://localhost:5432/postgres");
+		DataSourceBuilder<?> builder = DataSourceBuilder.derivedFrom(dataSource).type(SimpleDriverDataSource.class);
+		SimpleDriverDataSource testSource = (SimpleDriverDataSource) builder.build();
+		assertThat(testSource.getUsername()).isEqualTo("test");
+		assertThat(testSource.getUrl()).isEqualTo("jdbc:postgresql://localhost:5432/postgres");
+		assertThat(testSource.getPassword()).isEqualTo("secret");
+		assertThat(testSource.getDriver()).isInstanceOf(org.postgresql.Driver.class);
+	}
+
 	@Test // gh-31920
 	void buildWhenC3P0TypeSpecifiedReturnsExpectedDataSource() {
 		this.dataSource = DataSourceBuilder.create()
@@ -620,12 +634,10 @@ class DataSourceBuilderTests {
 
 	}
 
-	static class CustomDataSource extends LimitedCustomDataSource {
+	static class UrlCapableLimitedCustomDataSource extends LimitedCustomDataSource {
 
 		private String url;
 
-		private String driverClassName;
-
 		String getUrl() {
 			return this.url;
 		}
@@ -634,6 +646,13 @@ class DataSourceBuilderTests {
 			this.url = url;
 		}
 
+	}
+
+	static class CustomDataSource extends UrlCapableLimitedCustomDataSource {
+
+		private String driverClassName;
+
+
 		String getDriverClassName() {
 			return this.driverClassName;
 		}