[processing] Try directly interpreting string as CRS first

[nyalldawson]

...before falling back to alternatives like treating it as a map layer

Fixes #57494

[github-actions]

🪟 Windows builds ready!

Windows builds of this PR are available for testing here. Debug symbols for this build are available here.

(Built from commit 90c93ce)

[troopa81]

Do you mind adding tests?

[nyalldawson]

@troopa81

Do you mind adding tests?

I tried, but it's not possible (without unreasonable effort) -- there's already tests covering the functionality here, it's just the order of evaluation which has changed.

[agiudiceandrea]

@nyalldawson it seems to me the issue still occurs for some algorithm even using QGIS 3.37.0-Master b2a8801d76 : native:creategrid, native:createconstantrasterlayer, native:randompointsinextent, qgis:regularpoints, native:createrandomuniformrasterlayer, ...

[nyalldawson]

@agiudiceandrea

What command are you using to get them?

[agiudiceandrea]

@nyalldawson on an OSGeo4W Shell:

C:\OSGeo4W_V2_8>qgis_process-qgis-dev --version
QGIS 3.37.0-Master 'Master' (b2a8801d76)
QGIS code revision b2a8801d76
Qt version 5.15.13
Python version 3.12.3
Compiled against GDAL/OGR 3.10.0dev-39cad318b2
Running against GDAL/OGR 3.10.0dev-12dab86ca2
PROJ version 9.4.0
EPSG Registry database version v11.004 (2024-02-24)
GEOS version 3.12.1-CAPI-1.18.1
SQLite version 3.45.1
OS Windows 10 Version 1903
This copy of QGIS writes debugging output.

C:\OSGeo4W_V2_8>qgis_process-qgis-dev help native:creategrid
Create grid (native:creategrid)

----------------
Description
----------------
This algorithm creates a vector layer with a grid covering a given extent. Elements in the grid can be points, lines or polygons. The size and/or placement of each element in the grid is defined using a horizontal and vertical spacing. The CRS of the output layer must be defined. The grid extent and the spacing values must be expressed in the coordinates and units of this CRS. The top-left point (minX, maxY) is used as the reference point. That means that, at that point, an element is guaranteed to be placed. Unless the width and height of the selected extent is a multiple of the selected spacing, that is not true for the other points that define that extent.

----------------
Arguments
----------------

...

CRS: Grid CRS
ERROR: Status 2: File ProjectCrs could not be found
ERROR: Status 2: File ProjectCrs could not be found
        Default value:  ProjectCrs
        Argument type:  crs
        Acceptable values:
                - CRS as an auth ID (e.g. 'EPSG:3111')
                - CRS as a PROJ4 string (e.g. 'PROJ4:à')
                - CRS as a WKT string (e.g. 'WKT:à')
                - Path to a layer. The CRS of the layer is used.

...

The issue is due to the fact that such algorithms have the string "ProjectCrs" as default value for the CRS parameter, but such string is not a valid QgsCoordinateReferenceSystem, thus the check in

QGIS/src/core/processing/qgsprocessingparameters.cpp

Lines 3115 to 3122 in 90c93ce

	QString QgsProcessingParameterCrs::valueAsString( const QVariant &value, QgsProcessingContext &context, bool &ok ) const
	{
	if ( value.type() == QVariant::String )
	{
	const QgsCoordinateReferenceSystem crs( value.toString() );
	if ( crs.isValid() )
	return value.toString();
	}

still fails.

See

QGIS/src/core/processing/qgsprocessingutils.cpp

Lines 674 to 676 in 0c41c22

	// maybe special string
	if ( context.project() && crsText.compare( QLatin1String( "ProjectCrs" ), Qt::CaseInsensitive ) == 0 )
	return context.project()->crs();

[nyalldawson]

@agiudiceandrea fixed in #57576