fix(nimbus): catch FmlError when FmlClient fails to parse a manifest#15019
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Because * The FmlClient constructor can raise FmlError.ValidationError when a feature manifest has validation errors (e.g. a variable with both gecko-pref and default, which are now mutually exclusive) * NimbusFmlLoader.fml_client() did not catch this, causing a 500 on any page that calls get_invalid_fields_errors() for affected experiments * This was discovered via failing Fenix integration tests on PR #15002 This commit * Wraps the FmlClient() constructor in a try/except FmlError so invalid manifests are logged and skipped rather than crashing the page * Adds unit tests for the graceful degradation in both fml_client() and get_fml_errors() Fixes #15018
jaredlockhart
requested review from
freshstrangemusic,
mikewilli,
relud and
yashikakhurana
as code owners
relud
approved these changes
Mar 23, 2026
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Because
FmlClientconstructor can raiseFmlError.ValidationErrorwhen a feature manifest has validation errors (e.g., a variable with bothgecko-prefanddefault, which are now mutually exclusive as of the latest application-services build)NimbusFmlLoader.fml_client()did not catch this exception, so it propagated up and caused a 500 error on any page that callsget_invalid_fields_errors()(including the audience page during experiment creation)FIREFOX_FENIXUI tests failed withTimeoutExceptionbecause the audience page returned a 500This commit
FmlClient()constructor in atry/except FmlErrorso invalid manifests are logged and skipped rather than crashing the pagefml_client()andget_fml_errors()Fixes #15018