responsive.viewport meta missing

responsive.viewport-meta-missing

Rule ID: responsive.viewport-meta-missing Severity: WARN Category: responsive Target Standards: HTML Living Standard (Viewport Meta Element), Apple WebKit Safe Area Viewport Expansion Guidelines, W3C CSS Device Adaptation Module Level 1

---

1. Overview & Core Invariant

Warns when is missing width=device-width or viewport-fit=cover

Core Invariant:

" elements must declare both 'width=device-width' (preventing 980px virtual desktop zoom fallback) and 'viewport-fit=cover' (enabling safe area inset expansion on notched displays)."

---

2. Technical Grounding & Engine Realities

Omitting 'width=device-width' causes mobile browsers (WebKit and Chromium) to fall back to a 980px virtual desktop viewport, forcing users to pinch-zoom and rendering responsive media queries ineffective.

Omitting 'viewport-fit=cover' causes CSS safe area variables (env(safe-area-inset-*)) to evaluate to 0px on iOS devices, resulting in white letterboxing around sensor cutouts and disabling hardware-safe bottom docks.

Declaring both parameters ensures proportionate rendering across all smartphone screen densities and full hardware edge-to-edge layout immersion.

---

3. Vulnerability & Risk Taxonomy

Risk Vector	Severity	Impact
980px Virtual Desktop Zoom Fallback	HIGH	Mobile browsers scale down pages to fit a 980px virtual width, making text unreadable and disabling responsive layouts.
Safe Area Inset Failure and Letterboxing	MEDIUM	CSS env(safe-area-inset-bottom) evaluates to 0px, causing bottom bars to be obscured by hardware home indicators and displaying letterbox bars.

---

4. Non-Compliant Code Patterns (Bad Examples)

TSX (Viewport meta tag missing viewport-fit=cover):

<meta name="viewport" content="width=device-width, initial-scale=1.0" />

---

5. Compliant Implementation Patterns (Good Examples)

TSX (Complete mobile viewport configuration with device width and safe-area expansion):

<meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover" />

---

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.viewport-meta-missing"]

Loading

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.viewport-meta-missing directives.
4. Diagnostic Emission: Emits compiler-grade diagnostic on invariant violation.

---

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.viewport-meta-missing/:

flowchart TD
    subgraph GoldenCorpus ["1-SSOT Tri-Corpus Test Matrix for responsive.viewport-meta-missing"]
        subgraph P ["Positive Corpus (tests/correctness/responsive.viewport-meta-missing/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.viewport-meta-missing/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.viewport-meta-missing/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"]

Loading

• 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.

---

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.viewport-meta-missing intentional exception -->

// charites:ignore responsive.viewport-meta-missing intentional exception

---

9. Configuration Reference (charites.yaml)

rules:
  responsive.viewport-meta-missing:
    severity: warn # error | warn | info | off