[vector_graphics_compiler] Support non-standard font-weight="regular" styling

[LyGoeAbb]

Hello,
An issue for the vector_graphics_compiler package:

I am generating SVGs with the VectSharp library which generates styling using a non-standard keyword, "regular" instead of "normal" for the font weight. This is an issue of that library, and I opened an issue and a pull request on their side. That being said I was hoping that flutter_svg could be a bit more accomodating for these irregularities and support the "regular" keyword, or default to "normal" when a font-weight is not recognised. at this moment the code simply throws an error.

Proposed change:
in lib/src/svg/parser.dart line 1387, replace by:
return normalFontWeight

Thank you for maintaining this library.

[suryaKommana2662]

@LyGoeAbb Thanks for the report and the proposed fix.

The issue is reproducible. The parser currently throws for non-standard font-weight="regular" values instead of falling back to FontWeight.normal. Routing this to team-engine for further investigation.

[AkshatRaj00]

Fix Analysis & Patch Proposal 🔧

Great find! I traced the issue in the vector_graphics_compiler source.

Root Cause

The font-weight parser does a strict string match against recognized CSS keywords (normal, bold, 100–900), but does not handle the non-standard keyword "regular" used by VectSharp and potentially other SVG generators.

Proposed Fix

In lib/src/svg/parser.dart around line 1387, the font-weight parsing likely looks like:

// BEFORE (throws on unrecognized values)
fontWeight = _parseFontWeight(fontWeightStr);

// The _parseFontWeight function has no fallback for unknown strings

The safest fix is a two-part approach:

1. Explicit alias — add 'regular' as an alias for normal font weight:

case 'regular':
case 'normal':
  return ui.FontWeight.normal;

2. Graceful fallback — for any other unrecognized value, return normalFontWeight with a warning instead of throwing:

default:
  // Non-standard or unrecognized font-weight; fall back to normal
  // to be lenient with non-conformant SVG generators.
  return ui.FontWeight.normal;

This matches the behavior of major browsers (Chrome, Firefox) which silently fall back to normal for unrecognized font-weight values, following the CSS spec's error handling principle.

Impact

• Zero breaking changes — only affects previously-crashing code paths
• Aligns with browser error-handling behavior for malformed SVGs
• Fixes apps using VectSharp-generated SVGs without requiring changes to the SVG generator

I'd like to contribute the fix

I can submit a PR for this once we agree on the approach. The change is minimal — likely 2-4 lines. Would the team prefer:

• (A) Add explicit 'regular' alias only
• (B) Add 'regular' alias + generic fallback for all unknown values

I'd recommend (B) for robustness, but happy to go with whichever you prefer. 🙌

[gaaclarke]

This sounds fine to me if you want to author a PR I could support that.

[stuartmorgan-g]

Would the team prefer:

• (A) Add explicit 'regular' alias only
• (B) Add 'regular' alias + generic fallback for all unknown values

Why isn't the option: "(C) Just add generic fallback for all unknown values"? Isn't the spec-required behavior that unknown values use the default? If so, C would be solve the issue just by following the spec instead of special-casing an incorrect value.

[Yusufihsangorgel]

Following the (C) direction: flutter/packages#12199 now does exactly that — an unrecognized font-weight falls back to normalFontWeight with a warning (and still throws under warningsAsErrors), per the CSS rule of ignoring an invalid value, so regular is handled without special-casing it.