Warn when the output filename expression returns a NULL value or is wrong

[qgib]

Author Name: Harrissou Santanna (@DelazJ)
Original Redmine Issue: 13390

Redmine category:map_composer/printing

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Create an atlas and in output filename expression, put a wrong formula, something like 'output'||@atlasfeaturenum
Then export the atlas. all the process will go till the end even though no file will be generated.

I think that the user should be warned about the error:

• when he clicks out of the expression textbox
• or when he clicks on the export button

[qgib]

Author Name: Anita Graser (@anitagraser)

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• fixed_version_id was changed from Future Release - High Priority to Future Release - Nice to have
• priority_id was changed from High to Normal
• subject was changed from Print Composer : Warn when the output filename expression return a NULL value or is wrong to Warn when the output filename expression returns a NULL value or is wrong
• tracker_id was changed from 1 to 2

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0

[troopa81]

I faced a likely issue. If the field targeted in expression contains special character (/ \ or space character) the filename could be invalid, and you get a big error message. I'm wondering if we should not try to slugify the generated name to ensure filename validity.

If somebody stumble upon the same problem, I fixed it with replace_regexp

regexp_replace("output" || name_with_special_character, '[^\\w]', '_')

[DelazJ]

I'm wondering if we should not try to slugify the generated name to ensure filename validity.

@troopa81 you probably fall into #37225 case

[troopa81]

@DelazJ Yes indeed, makes sense! Thanks for the link