No more expression checks in the Processing raster calculator algorithms

[DelazJ]

What is the bug or the crash?

In the old "Raster calculator" algorithm and the one in "Raster" menu, there is a check done on validity of the expression you write. The result is displayed at the bottom of the expression textbox.
In the new (virtual or not) "Raster calculator" algorithms, there is no feedback about expression validity. The label widget that displays the result is still present in the ui file at the bottom of the expression box, but it does not seem reused.

Steps to reproduce the issue

1. Add raster layer(s) to a project
2. Open Processing Raster calculator algorithm
3. Press the expression button, opening the "Raster calculator expression" widget
4. Type anything you want and see that nothing happens and you can safely hit the OK button (in vector context, an invalid expression use to disable the OK button)

In old version there was no specific widget for expressions but you'd get a red "Expression is not valid"

Versions

master (a161141) on Windows 10

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response

[fpirotti]

+1 on this issue... the new raster calculator seems to have lost a lot of the positive aspects. As others suggested a "recent expressions" would also be great. Also integration with model builder will be an issue.