Summary
Computing a style that references circular CSS custom properties causes an uncatchable native stack overflow and terminates the host process. This reproduces using AngleSharp only, without a JavaScript engine or browser adapter.
Confirmed with AngleSharp 1.7.2, AngleSharp.Css 1.0.2, .NET 10.0.11, macOS arm64. The standalone program below exits with code 134.
Duplicate search
I searched open and closed issues for circular references, cycles, recursion, stack overflow, custom properties, and var. Related closed reports are #62 (adding variable resolution), #171 (variables in shorthand properties), and #184 (inheritance); their descriptions and comments do not cover cycle-induced process termination.
Reproduction
Create a console project:
dotnet new console -n CssCycleRepro -f net10.0
cd CssCycleRepro
dotnet add package AngleSharp --version 1.7.2
dotnet add package AngleSharp.Css --version 1.0.2
Replace Program.cs with:
using AngleSharp;
using AngleSharp.Css;
using AngleSharp.Dom;
using var context = BrowsingContext.New(Configuration.Default.WithCss());
using var document = await context.OpenAsync(response => response.Content(
"""
<!doctype html>
<style>
:root { --a: var(--b); --b: var(--a); }
button { color: var(--a); }
</style>
<button>Save</button>
"""));
Console.WriteLine(document.QuerySelector("button")!.ComputeCurrentStyle().GetPropertyValue("color"));Run in a separate process, because the failure terminates it:
Actual result
Stack overflow. followed by repeating frames:
AngleSharp.Css.Values.CssComputeContext.Resolve(System.String)
AngleSharp.Css.Dom.CssProperty+PropertyComputeContext.Resolve(System.String)
AngleSharp.Css.Values.CssVarValue.Compute(ICssComputeContext)
AngleSharp.Css.Values.CssReferenceValue.ICssValue.Compute(ICssComputeContext)
AngleSharp.Css.Values.CssVarValue.Compute(ICssComputeContext)
AngleSharp.Css.Values.CssReferenceValue.ICssValue.Compute(ICssComputeContext)
...
The process exits with code 134 rather than returning a computed style or a catchable exception.
Expected result
Per CSS Variables §2.3: Resolving Dependency Cycles, each custom property in the cycle becomes guaranteed-invalid. A consuming var(--a, red) should use its fallback; without a fallback the consuming declaration is invalid at computed-value time. Neither should terminate the host.
Relevant regression cases include --a:var(--a), multi-variable cycles, cycles with internal fallback values, edges in unused fallbacks such as --a:var(--present,var(--a)), and inheritance of already-resolved custom properties. A dependent property outside a cycle may recover with its own fallback, so marking all dependencies invalid is not sufficient.
Impact / downstream context
Found while embedding AngleSharp.Css in Jint.Browser: sebastienros/jint#3851. A page's computed style, geometry, or accessibility query can terminate the entire shared browser process. try/catch is not a workaround for StackOverflowException; cycle handling has to occur before recursive value computation.
Summary
Computing a style that references circular CSS custom properties causes an uncatchable native stack overflow and terminates the host process. This reproduces using AngleSharp only, without a JavaScript engine or browser adapter.
Confirmed with AngleSharp 1.7.2, AngleSharp.Css 1.0.2, .NET 10.0.11, macOS arm64. The standalone program below exits with code 134.
Duplicate search
I searched open and closed issues for circular references, cycles, recursion, stack overflow, custom properties, and
var. Related closed reports are #62 (adding variable resolution), #171 (variables in shorthand properties), and #184 (inheritance); their descriptions and comments do not cover cycle-induced process termination.Reproduction
Create a console project:
dotnet new console -n CssCycleRepro -f net10.0 cd CssCycleRepro dotnet add package AngleSharp --version 1.7.2 dotnet add package AngleSharp.Css --version 1.0.2Replace
Program.cswith:Run in a separate process, because the failure terminates it:
Actual result
Stack overflow.followed by repeating frames:The process exits with code 134 rather than returning a computed style or a catchable exception.
Expected result
Per CSS Variables §2.3: Resolving Dependency Cycles, each custom property in the cycle becomes guaranteed-invalid. A consuming
var(--a, red)should use its fallback; without a fallback the consuming declaration is invalid at computed-value time. Neither should terminate the host.Relevant regression cases include
--a:var(--a), multi-variable cycles, cycles with internal fallback values, edges in unused fallbacks such as--a:var(--present,var(--a)), and inheritance of already-resolved custom properties. A dependent property outside a cycle may recover with its own fallback, so marking all dependencies invalid is not sufficient.Impact / downstream context
Found while embedding AngleSharp.Css in Jint.Browser: sebastienros/jint#3851. A page's computed style, geometry, or accessibility query can terminate the entire shared browser process.
try/catchis not a workaround forStackOverflowException; cycle handling has to occur before recursive value computation.