responsive.aspect ratio overflow

responsive.aspect-ratio-overflow

Rule ID: responsive.aspect-ratio-overflow Severity: WARN Category: responsive Target Standards: W3C CSS Box Sizing Module Level 4 (The aspect-ratio Property), WCAG 2.2 SC 1.4.10 (Reflow - Level AA), Responsive Media & Video Embed Best Practices

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1. Overview & Core Invariant

Warns against fixed aspect-ratio combined with rigid static heights without fluid width boundaries on mobile viewports

Core Invariant:

"Elements specifying an explicit 'aspect-*' ratio must not pair it with a rigid fixed height without fluid width constraints ('w-full' or 'max-w-full'), which forces width computation to expand beyond narrow mobile screens."

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2. Technical Grounding & Engine Realities

The CSS 'aspect-ratio' property computes the corresponding dimension when one dimension is defined. When an element specifies 'aspect-video' (16/9) and also sets 'h-[450px]' without a fluid width boundary ('w-full' or 'max-w-full'), the browser calculates width as 450 * (16/9) = 800px.

On a 360px mobile screen, an 800px computed width immediately blows out the layout horizontally, forcing horizontal scrolling and clipping sibling elements.

Charites detects conflicting aspect-ratio and rigid height definitions, recommending fluid widths ('w-full aspect-video') or letting height derive naturally from fluid container width.

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3. Vulnerability & Risk Taxonomy

Risk Vector	Severity	Impact
Massive Horizontal Layout Blowout via Derived Aspect Width	HIGH	Derived width expands to 800px+ on mobile screens when static height is combined with aspect-ratio.
Conflicting Spatial Dimension Constraints	MEDIUM	Media elements distort or overflow their parent grid/flex containers.

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4. Non-Compliant Code Patterns (Bad Examples)

TSX (Aspect ratio paired with rigid fixed height forcing excessive computed width):

<div className="aspect-video h-96 bg-black rounded-lg">
  <video src="/hero.mp4" controls />
</div>

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5. Compliant Implementation Patterns (Good Examples)

TSX (Fluid aspect ratio deriving height naturally from available width):

<div className="w-full aspect-video bg-black rounded-lg">
  <video src="/hero.mp4" controls className="w-full h-full object-cover" />
</div>

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6. Detection & Verification Pipeline (How The Rule Evaluates Code)

This rule evaluates source code through the standard AST inspection pipeline:

flowchart TD
    Node["AST Node (Astro / TSX element)"] --> Inspect["1. Inspect Element & Attributes"]
    Inspect --> Invariant{"2. Evaluate Rule Invariant"}
    Invariant -- "Compliant" --> Safe["Pass"]
    Invariant -- "Non-Compliant" --> IgnoreCheck{"3. Check charites:ignore directive"}
    IgnoreCheck -- "Ignored" --> Safe
    IgnoreCheck -- "Not Ignored" --> Diag["4. Emit Diagnostic: responsive.aspect-ratio-overflow"]

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Step-by-Step Evaluation:

1. AST Traversal: Visits normalized ir.Node structures during AST streaming.
2. Invariant Check: Compares node attributes against rule invariants.
3. Directive Suppression Check: Honors inline charites:ignore responsive.aspect-ratio-overflow directives.
4. Diagnostic Emission: Emits compiler-grade diagnostic on invariant violation.

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7. Verification & Test Harness (How The Test Works: 1-SSOT Tri-Corpus)

This rule is rigorously tested and validated across the canonical 1-SSOT Tri-Corpus in tests/correctness/responsive.aspect-ratio-overflow/:

flowchart TD
    subgraph GoldenCorpus ["1-SSOT Tri-Corpus Test Matrix for responsive.aspect-ratio-overflow"]
        subgraph P ["Positive Corpus (tests/correctness/responsive.aspect-ratio-overflow/positive/)"]
            P1["P1: Obvious Direct Violation"]
            P2["P2: Indirect / Variant Concatenation"]
            P3["P3: Helper / clsx / cn Wrapper"]
            P4["P4: Deeply Nested Elements"]
            P5["P5: Aliased Imports / Re-exports"]
        end
        subgraph N ["Negative Corpus (tests/correctness/responsive.aspect-ratio-overflow/negative/)"]
            N1["N1: Valid Design Tokens"]
            N2["N2: Explicit charites:ignore Directive"]
            N3["N3: Third-Party / Vendor Components"]
            N4["N4: Clean Semantic HTML"]
            N5["N5: Untokenized Custom Values (Banana Test)"]
        end
        subgraph A ["Adversarial Corpus (tests/correctness/responsive.aspect-ratio-overflow/adversarial/)"]
            A1["A1: Template Literal Interpolations"]
            A2["A2: Ternary Conditional Expressions"]
            A3["A3: Spread Properties & Dynamic Overrides"]
            A4["A4: Dynamic Object Class Syntax"]
            A5["A5: Shadowed Variable Identifiers"]
            A6["A6: Nested Closures & HOC Wrappers"]
            A7["A7: Obfuscated Classes & Cyclic Tokens"]
        end
    end

    P --> TestRunner["Automated Runner (rule_test.go)"]
    N --> TestRunner
    A --> TestRunner
    TestRunner --> Gates["Quality Gates: Zero Panic, Zero False-Positive, Zero Bypass"]

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• Positive Fixtures (P1-P5): Verified to trigger diagnostics at exact lines and column spans.
• Negative Fixtures (N1-N5): Verified to produce zero diagnostics on valid tokens and legitimate exemptions.
• Adversarial Fixtures (A1-A7): Verified to prevent evasion across dynamic expressions, string interpolations, and cyclic references.

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8. How to Suppress (Ignore Directives)

If this pattern is required for an intentional exception, suppress the diagnostic using the canonical Charites Rule ID:

<!-- charites:ignore responsive.aspect-ratio-overflow intentional exception -->

// charites:ignore responsive.aspect-ratio-overflow intentional exception

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9. Configuration Reference (charites.yaml)

rules:
  responsive.aspect-ratio-overflow:
    severity: warn # error | warn | info | off