[Bug]: "Show input fields" on a transform shows a field that is NOT available in the stream

[gmitter-ef]

Apache Hop version?

2.11.0

Java version?

OpenJDK 17

Operating system

Windows

What happened?

See the attachments. Basis is samples/transforms/json-input-basic.hpl.

Bug shows in version json-input-basic_2.hpl (see attached):
4876.zip

• open json-input-basic.hpl from samples/transforms
• Add a parameter to the pipeline "param1" with default value "test"
• Add a "Get variables" transform to read it into the stream at the beginning
• Add a "Write to log" tansform at the end, include all available fields (including param1)
• try to run the pipeline ==> error "Cannot find field [param1] in the input stream!"
  ** kind of plausible, as probably JSON input transform that reads a FILE should be the first transform in a pipeline
• click on "Show input fields" of the "Write to log" transform: param1 shows up! This should NOT be the case in my opinion and is totally confusing.

json-input-basic_3.hpl: when reading the json from a field, everything workxs
json-input-basic_4.hpl: when doing the "Get variables" transform AFTER the json input, it also works

Issue Priority

Priority: 3

Issue Component

Component: Hop Gui, Component: Transforms

[shlxue]

I checked this hpl: this is a bug of JSON Input transform. If don't use previous fields as Json file source: Ignore all input fields.

In fact, I am more concerned about another issue:
What's is the input transforms?
The default behavior of a new data stream initiator should be to ignore all previous fields.

Is the rule allowed to be broken? Like JSON input transform: pass previous fields to downstream

[hansva]

You are right that most input transforms do not pass previous data, but I am not sure it is a hard rule at the moment...
However, it is confusing that some do and some don't, especially if the metadata makes you think it does.

We might have to take a look and see which do and which don't and align and or document it.