How to fix "ICU Syntax Error: Expected > "identifier" but found "0"." error in Flutter 3.7.0

Question

After Updating to Flutter 3.7.0 i get this error message when i build my App:

[app_en.arb:scanCode_fieldNotMatched] ICU Syntax Error: Expected "identifier" but found "0". field to match is "{0}"

It seems as if something had changed in how the variables are written in the .arb localization files.

Answer 1

UPDATE 1: Escape syntax characters!

If what you are trying is to use the characters {, }, ' (or any other syntax character for that matter) in your strings, then you will have to escape them. To do that enable the use-escaping flag by adding the following to l10n.yaml

use-escaping: true

Now use pairs of single quotes to escape syntax characters, like "{". To escape single quotes you just have to write it as a double-single quote as follows:

{
  "some_text": "Using the '{' character '{isn''t}' trivial?"
}

More details on this in the flutter docu.

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Update 2: If you are using a Chinese Mirror for Flutter

Follow details in this issue.

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Original answer to my punctual problem

I found out that the reason for this error is that in Flutter 3.7

Internationalization support has been completely revamped! [they]’ve completely rewritten the gen-l10n tool...

as stated in a release post.

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Previously i was declaring strings in my .arb file as follows

"scanCode_fieldNotMatched": "field to match is \"{0}\"",

where afterwards i was replacing {0} by some other value.

Well, it seems that now the gen-l10n tool takes what is between brackets as special parameters, and the name "0" is not accepted so i had to change my string to

"scanCode_fieldNotMatched": "field to match is \"{value0}\"",

and AppLocalizations can be now called as:

AppLocalizations.of(context)!.scanCode_fieldNotMatched("something here to replace value0!")

Further details on this can be found here: Placeholders, plurals, and selects in Flutter.

Answer 2

In my case, it was due to a translation string in my arb file for intl package. I had:

"{x, plural, =1{item}, other{items}}" (worked fine in previous versions)

This broke in Flutter 3.7. The solution for me was removing a comma:

"{x, plural, =1{item} other{items}}" (works in Flutter 3.7)