Hello,
I've encountered a significant parsing issue with PlantUML versions 1.2025.3 (local) and 1.2025.4beta2 (on plantuml.com) when trying to create activity diagrams with stereotyped activities or standard data objects. This consistently results in a "Syntax Error? (Assumed diagram type: sequence)" error. I've searched the forum and GitHub issues but haven't found an exact match for this combination of failures in these specific versions, though I apologize if this is a duplicate.
Here are the details and minimal reproducible examples:
PlantUML Version(s) Affected:
- Observed directly on plantuml.com/plantuml server: 1.2025.4beta2
- Similar behavior observed locally with: 1.2025.3
Bug Description:
PlantUML versions around 1.2025.3 / 1.2025.4beta2 fail to correctly parse standard activity diagram syntax, frequently resulting in a "Syntax Error? (Assumed diagram type: sequence)" error. This occurs even with very minimal examples.
The primary triggers for this misparsing appear to be:
Stereotyped Activities: The syntax skinparam activity<<StereotypeName>> { ... } combined with activity "Label" as Alias <<StereotypeName>> consistently fails.
- Example that fails (error on the activity line):
@startuml MinimalStereotypeFail
skinparam activity<<IO>> {
shape data
}
activity "Test Activity" as TA <<IO>>
@enduml
Data Object Syntax (:"Text";): The syntax :"Text"; as Alias for defining data objects (which should render as parallelograms) also seems to trigger the parsing error when used in an activity diagram context, particularly if it appears early in the diagram definition.
- Example that fails (error on the :"Desired\naccess"; line):
@startuml MinimalDataObjectFail
actor "Access token" as User
:"Desired\naccess"; as DesiredAccess ' Data object
activity "Some Process" as P1
User --> P1
DesiredAccess --> P1
@enduml
Basic Activity Definition (in some complex contexts): In our attempts to build a full flowchart, even after removing stereotypes and data objects, the parser still sometimes failed on standard activity "Label" as Alias lines if the preceding structure was complex or involved other problematic syntax. The screenshot attached (or linked if this is a web form) shows the "TEST_4_COMPROMISE" code from our previous attempts still failing on line 35 (activity "Desired\naccess" as DesiredAccess) on the online server.
Expected Behavior:
The provided PlantUML code, especially the minimal examples, should parse correctly as activity diagrams without error, and elements should be rendered according to the syntax used (e.g., stereotyped activities should adopt their defined shapes, data objects should appear as parallelograms).
Actual Behavior:
The parser throws a "Syntax Error? (Assumed diagram type: sequence)" error, indicating it failed to recognize the diagram as an activity diagram and defaulted to an incorrect type.
Steps to Reproduce (using plantuml.com/plantuml):
Impact:
This bug makes it impossible to use standard features like activity stereotypes or data objects in activity diagrams with these PlantUML versions, severely limiting the ability to create visually accurate and semantically correct flowcharts. It also affects the parsing of more complex, but otherwise valid, activity diagrams.
