Due to swc format limitation, sources cannot be embedded into binaries. That's why most of time, each dependencies will have a defined source attachments in .actionScriptProperties file. flex:eclipse can automatically linked source attachment to dependencies with a property named "sourceAttachments". Just map the groupId and artifactId to the sources location.
<configuration> <sourceAttachments> <sourcePathEntry> <groupId>com.adobe.flex.sdkcore</groupId> <artifactId>framework</artifactId> <sourcePath>PATH/TO/YOUR/SOURCES/FOLDER/flex_sdk_18.104.22.16858/frameworks/projects/framework/src</sourcePath> </sourcePathEntry> </sourceAttachments> <configuration>