Description

When using the !include directive with relative paths and previewing a UML diagram, instead of the diagram a rendered error message is displayed stating that the file to be included could not be found.

Looking at the error message it is clear that the absolute path is not resolved correctly. It starts with the workspace as root instead of the file systems root.

Steps to reproduce

1. Create the following two files inside an Eclipse project: foo.plantuml, bar.plantuml, contents see below.
2. Open the PlantUML preview: "Window" → "Show View" → "Other..." , Pick view "PlantUML"
3. Open foo.plantuml with the Eclipse-internal text editor
4. The following PlantUML error message is rendered in the preview view:

   Cannot include /<path inside workspace>/bar.plantuml

File A: foo.plantuml

@startuml
!include bar.plantuml
class "Foo"
@enduml

File B: bar.plantuml

@startuml
class "Bar"
@enduml

Expected Behavior

Relative include paths are resolved to absolute paths starting at the file system root.

Actual Behavior

Relative include paths are resolved to absolute paths starting at the workspace root. Inclusion fails.

Environment

• Eclipse DE for Java Developers, Version: Oxygen.3a Release (4.7.3a), Build id: 20180405-1200
• PlantUML Feature, Version: 1.1.20
• PlantUML Library Feature, Version: 1.2018.9
• Linux, v.4.18.12-200.fc28.x86_64, x86_64
• gtk 3.22.30

Also tested on Eclipse Photon with the same result.
PlantUML plugin 1.1.19 in contrast worked.