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LibWeb: Check CanvasTextDrawingStyles.font assignment is valid

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Checking that the string parsed for the `font` property is not enough,
the spec also wants to rule out CSS-wide keywords like `inherit`. The
simplest way to do so is to check if it's a ShorthandStyleValue, which
also rules out use of `var()`; this matches other browsers' behaviour.

The newly-added test would previously crash, and now doesn't. :^)
This commit is contained in:
Sam Atkins 2024-07-23 16:14:26 +01:00 committed by Andreas Kling
parent 54066ec5a4
commit 64d45afd8a
Notes: github-actions[bot] 2024-07-23 16:01:08 +00:00 
Author: https://github.com/AtkinsSJ
Commit: https://github.com/LadybirdBrowser/ladybird/commit/64d45afd8a6
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/791
3 changed files with 23 additions and 1 deletions
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4
Tests/LibWeb/Text/expected/canvas/invalid-font-property.txt Normal file
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@ -0,0 +1,4 @@
normal normal 20px SerenitySans
normal normal 20px SerenitySans
normal normal 20px SerenitySans
normal normal 20px SerenitySans

15
Tests/LibWeb/Text/input/canvas/invalid-font-property.html Normal file
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@ -0,0 +1,15 @@
<script src="../include.js"></script>
<script>
test(() => {
let canvas = document.createElement("canvas");
let context = canvas.getContext("2d");
context.font = '20px SerenitySans';
println(context.font);
context.font = 'inherit'; // CSS-wide keywords are not allowed
println(context.font);
context.font = 'var(--font-size, 30px) Arial'; // Variables are not allowed here
println(context.font);
context.font = '!!!'; // Invalid value, should be ignored.
println(context.font);
});
</script>

5
Userland/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.h
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@ -41,11 +41,14 @@ public:
// The font IDL attribute, on setting, must be parsed as a CSS <'font'> value (but without supporting property-independent style sheet syntax like 'inherit'),
// and the resulting font must be assigned to the context, with the 'line-height' component forced to 'normal', with the 'font-size' component converted to CSS pixels,
// and with system fonts being computed to explicit values.
// FIXME: with the 'line-height' component forced to 'normal'
// FIXME: with the 'font-size' component converted to CSS pixels
auto parsing_context = CSS::Parser::ParsingContext { reinterpret_cast<IncludingClass&>(*this).realm() };
auto font_style_value_result = parse_css_value(parsing_context, font, CSS::PropertyID::Font);
// If the new value is syntactically incorrect (including using property-independent style sheet syntax like 'inherit' or 'initial'), then it must be ignored, without assigning a new font value.
if (!font_style_value_result) {
// NOTE: ShorthandStyleValue should be the only valid option here. We implicitly VERIFY this below.
if (!font_style_value_result || !font_style_value_result->is_shorthand()) {
return;
}
my_drawing_state().font_style_value = font_style_value_result.release_nonnull();