All files / packages/sds-customization-compliance/src/checks/structural no-bare-bem-hook-writes.ts

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/**
 * Rule 5 (writes): hook writes on bare modifier or element selectors
 * leak via custom-property inheritance.
 *
 * Modifiers and BEM elements are system-owned painting vocabulary;
 * customers don't override them directly (they compose against the
 * component's base). What this check enforces is **cascade hygiene**:
 * a bare modifier or element class can match any element carrying
 * that class — including a wrapper that doesn't carry the component
 * root. When that happens, the rule's `--slds-c-*` write sets a
 * custom property on the wrapper, which inherits down to every real
 * component instance rendered inside that wrapper, repainting them
 * with values they never asked for.
 *
 * The fix is to anchor the selector to the component root so the
 * rule only matches inside an actual component instance.
 *
 * Companion check: {@link noBareBemPaintRules} flags bare-selector
 * rules that paint without writing hooks (the no-cascade-amplification
 * variant of the same anchoring problem).
 *
 * Carveout — relay routing: a rule whose hook writes all use the
 * `var(<relay>, revert-layer)` shape is a Path 4 recipe-level relay
 * route, not an unconditional override. `revert-layer` defers to
 * the lower layer when the relay isn't set, so the rule does not
 * unconditionally repaint unrelated descendants. See
 * `helpers/relayRouting.ts`.
 */
 
import { classifySurface, isAnchoringIncorrect, type SelectorSurface } from '../helpers/selectorSurface.js';
import { resolveBemRoot, resolveHookPrefix } from '../helpers/resolveHookPrefix.js';
import { isRelayRoutingRule } from '../helpers/relayRouting.js';
import type { ComplianceCheck, ComplianceRow, Offender } from '../../types.js';
import {
  declLocation,
  failRow,
  notRunYetRow,
  passRow,
  themeLayerFilesFor,
  visitHookWriteRules,
} from './internals.js';
 
const ID = 'structural-no-bare-bem-hook-writes';
const LABEL = 'No hook writes on bare child-element selectors';
const CATEGORY = 'customer-reach' as const;
 
function fixForSurface(_surface: SelectorSurface, part: string, prop: string, prefix: string): string {
  // Only `system-element-bare` reaches this function; the surface
  // parameter is kept on the signature so future surface variants
  // can branch here without an API change.
  return (
    `Anchor \`${part}\` as a root-anchored descendant (\`.slds-${prefix} .slds-${prefix}__element\`) ` +
    `so the rule only matches inside an actual \`.slds-${prefix}\` instance. ` +
    `Without the anchor, this rule's \`${prop}\` write inherits to every \`.slds-${prefix}\` descendant ` +
    `whenever the element class is placed on an element outside a \`.slds-${prefix}\`. ` +
    `(Bare modifier classes are exempt — they're component-prefixed and only ever land on \`.slds-${prefix}\` instances.)`
  );
}
 
export const noBareBemHookWrites: ComplianceCheck = (input): ComplianceRow => {
  const files = themeLayerFilesFor(input);
  if (!files) return notRunYetRow(ID, LABEL, CATEGORY);
  if (files.length === 0) {
    return passRow(ID, LABEL, 'Component has no theme or theme-base files; nothing to check.', CATEGORY);
  }
 
  const ownPrefix = resolveBemRoot(input.componentName);
  const ownHookPrefix = resolveHookPrefix(input.componentName);
  const offenders: Offender[] = [];
 
  for (const file of files) {
    visitHookWriteRules(file, ({ rule, hookDecls }) => {
      // Relay-routing carveout: a rule whose hook writes all forward
      // INTO an embedded component's hook (LHS foreign to this
      // component) FROM this component's own hook namespace (RHS
      // `var(--slds-c-{ownHookPrefix}-...)`) with a `revert-layer`
      // fallback is an embedding-component relay, not an unanchored
      // modifier override.
      Iif (isRelayRoutingRule(hookDecls, ownHookPrefix)) return;
      const parts = rule.selector
        .split(',')
        .map((p) => p.trim())
        .filter(Boolean);
      for (const part of parts) {
        const surface = classifySurface(part, input.componentName);
        if (!isAnchoringIncorrect(surface)) continue;
        for (const decl of hookDecls) {
          offenders.push({
            selector: part,
            hook: decl.prop,
            location: declLocation(file, decl),
            fix: fixForSurface(surface, part, decl.prop, ownPrefix),
          });
        }
      }
    });
  }
 
  if (offenders.length === 0) {
    return passRow(
      ID,
      LABEL,
      'Every hook write on a child-element selector is anchored to the component root, so the assignment cannot leak into unrelated cascade contexts.',
      CATEGORY,
    );
  }
 
  return failRow(
    ID,
    LABEL,
    `${offenders.length} hook write${offenders.length === 1 ? '' : 's'} on bare child-element selectors. ` +
      `BEM-element class shapes (\`.slds-${ownPrefix}__…\`) can land as descendants of any cascade context; ` +
      `without an instance anchor (\`.slds-${ownPrefix} .slds-${ownPrefix}__…\`), the hook write inherits down ` +
      `wherever the element class lands and repaints unrelated descendants. ` +
      `Anchor each selector to the component root per RFC 1157 Rule 5. ` +
      `Bare modifier selectors are exempt — they're component-prefixed and only ever land on real instances.`,
    offenders,
  );
};