Fix media type matching in unions to use file extension heuristics#2894
Merged
antoniosarosi merged 2 commits intocanaryfrom Dec 31, 2025
Merged
Fix media type matching in unions to use file extension heuristics#2894antoniosarosi merged 2 commits intocanaryfrom
antoniosarosi merged 2 commits intocanaryfrom
Conversation
When coercing a value like `{ file: "document.pdf" }` to a union type
like `(image | pdf)`, the code previously matched the first variant
(`image`) regardless of the file extension, resulting in invalid MIME
types like "image/pdf".
This change adds extension-based matching for media types in unions:
- Extract file extension from `{ file: "..." }` or `{ url: "..." }`
- Match against the appropriate media type based on extension
- Fall back to original first-match behavior if no extension match
Also adds strict media type matching when coercing already-coerced
BamlValue::Media to ensure the media_type field matches the target,
with fallback cases for backwards compatibility.
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Summary
When coercing a value like
{ file: "document.pdf" }to a union type like(image | pdf), the code previously matched the first variant (image) regardless of the file extension, resulting in invalid MIME types likeimage/pdf.This change:
.pdf,.png,.mp3, etc.){ file: "..." }and{ url: "..." }forms, including URLs with query paramsBamlValue::Mediawith fallback for backwards compatibilityFix #2782
Test plan
(image | pdf)[]union now correctly identifies PDF files[<application_placeholder base64>]instead of[<image_placeholder base64>]