planning

node_modules/@mapbox/mapbox-gl-style-spec/expression/parsing_context.js

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+// @flow
+
+import Scope from './scope.js';
+import {checkSubtype} from './types.js';
+import ParsingError from './parsing_error.js';
+import Literal from './definitions/literal.js';
+import Assertion from './definitions/assertion.js';
+import Coercion from './definitions/coercion.js';
+import EvaluationContext from './evaluation_context.js';
+import CompoundExpression from './compound_expression.js';
+import CollatorExpression from './definitions/collator.js';
+import Within from './definitions/within.js';
+import {isGlobalPropertyConstant, isFeatureConstant} from './is_constant.js';
+import Var from './definitions/var.js';
+
+import type {Expression, ExpressionRegistry} from './expression.js';
+import type {Type} from './types.js';
+
+/**
+ * State associated parsing at a given point in an expression tree.
+ * @private
+ */
+class ParsingContext {
+    registry: ExpressionRegistry;
+    path: Array<number>;
+    key: string;
+    scope: Scope;
+    errors: Array<ParsingError>;
+
+    // The expected type of this expression. Provided only to allow Expression
+    // implementations to infer argument types: Expression#parse() need not
+    // check that the output type of the parsed expression matches
+    // `expectedType`.
+    expectedType: ?Type;
+
+    constructor(
+        registry: ExpressionRegistry,
+        path: Array<number> = [],
+        expectedType: ?Type,
+        scope: Scope = new Scope(),
+        errors: Array<ParsingError> = []
+    ) {
+        this.registry = registry;
+        this.path = path;
+        this.key = path.map(part => `[${part}]`).join('');
+        this.scope = scope;
+        this.errors = errors;
+        this.expectedType = expectedType;
+    }
+
+    /**
+     * @param expr the JSON expression to parse
+     * @param index the optional argument index if this expression is an argument of a parent expression that's being parsed
+     * @param options
+     * @param options.omitTypeAnnotations set true to omit inferred type annotations.  Caller beware: with this option set, the parsed expression's type will NOT satisfy `expectedType` if it would normally be wrapped in an inferred annotation.
+     * @private
+     */
+    parse(
+        expr: mixed,
+        index?: number,
+        expectedType?: ?Type,
+        bindings?: Array<[string, Expression]>,
+        options: {typeAnnotation?: 'assert' | 'coerce' | 'omit'} = {}
+    ): ?Expression {
+        if (index) {
+            return this.concat(index, expectedType, bindings)._parse(expr, options);
+        }
+        return this._parse(expr, options);
+    }
+
+    _parse(expr: mixed, options: {typeAnnotation?: 'assert' | 'coerce' | 'omit'}): ?Expression {
+        if (expr === null || typeof expr === 'string' || typeof expr === 'boolean' || typeof expr === 'number') {
+            expr = ['literal', expr];
+        }
+
+        function annotate(parsed, type, typeAnnotation: 'assert' | 'coerce' | 'omit') {
+            if (typeAnnotation === 'assert') {
+                return new Assertion(type, [parsed]);
+            } else if (typeAnnotation === 'coerce') {
+                return new Coercion(type, [parsed]);
+            } else {
+                return parsed;
+            }
+        }
+
+        if (Array.isArray(expr)) {
+            if (expr.length === 0) {
+                return this.error(`Expected an array with at least one element. If you wanted a literal array, use ["literal", []].`);
+            }
+
+            const op = expr[0];
+            if (typeof op !== 'string') {
+                this.error(`Expression name must be a string, but found ${typeof op} instead. If you wanted a literal array, use ["literal", [...]].`, 0);
+                return null;
+            }
+
+            const Expr = this.registry[op];
+            if (Expr) {
+                let parsed = Expr.parse(expr, this);
+                if (!parsed) return null;
+
+                if (this.expectedType) {
+                    const expected = this.expectedType;
+                    const actual = parsed.type;
+
+                    // When we expect a number, string, boolean, or array but have a value, wrap it in an assertion.
+                    // When we expect a color or formatted string, but have a string or value, wrap it in a coercion.
+                    // Otherwise, we do static type-checking.
+                    //
+                    // These behaviors are overridable for:
+                    //   * The "coalesce" operator, which needs to omit type annotations.
+                    //   * String-valued properties (e.g. `text-field`), where coercion is more convenient than assertion.
+                    //
+                    if ((expected.kind === 'string' || expected.kind === 'number' || expected.kind === 'boolean' || expected.kind === 'object' || expected.kind === 'array') && actual.kind === 'value') {
+                        parsed = annotate(parsed, expected, options.typeAnnotation || 'assert');
+                    } else if ((expected.kind === 'color' || expected.kind === 'formatted' || expected.kind === 'resolvedImage') && (actual.kind === 'value' || actual.kind === 'string')) {
+                        parsed = annotate(parsed, expected, options.typeAnnotation || 'coerce');
+                    } else if (this.checkSubtype(expected, actual)) {
+                        return null;
+                    }
+                }
+
+                // If an expression's arguments are all literals, we can evaluate
+                // it immediately and replace it with a literal value in the
+                // parsed/compiled result. Expressions that expect an image should
+                // not be resolved here so we can later get the available images.
+                if (!(parsed instanceof Literal) && (parsed.type.kind !== 'resolvedImage') && isConstant(parsed)) {
+                    const ec = new EvaluationContext();
+                    try {
+                        parsed = new Literal(parsed.type, parsed.evaluate(ec));
+                    } catch (e) {
+                        this.error(e.message);
+                        return null;
+                    }
+                }
+
+                return parsed;
+            }
+
+            return this.error(`Unknown expression "${op}". If you wanted a literal array, use ["literal", [...]].`, 0);
+        } else if (typeof expr === 'undefined') {
+            return this.error(`'undefined' value invalid. Use null instead.`);
+        } else if (typeof expr === 'object') {
+            return this.error(`Bare objects invalid. Use ["literal", {...}] instead.`);
+        } else {
+            return this.error(`Expected an array, but found ${typeof expr} instead.`);
+        }
+    }
+
+    /**
+     * Returns a copy of this context suitable for parsing the subexpression at
+     * index `index`, optionally appending to 'let' binding map.
+     *
+     * Note that `errors` property, intended for collecting errors while
+     * parsing, is copied by reference rather than cloned.
+     * @private
+     */
+    concat(index: number, expectedType?: ?Type, bindings?: Array<[string, Expression]>): ParsingContext {
+        const path = typeof index === 'number' ? this.path.concat(index) : this.path;
+        const scope = bindings ? this.scope.concat(bindings) : this.scope;
+        return new ParsingContext(
+            this.registry,
+            path,
+            expectedType || null,
+            scope,
+            this.errors
+        );
+    }
+
+    /**
+     * Push a parsing (or type checking) error into the `this.errors`
+     * @param error The message
+     * @param keys Optionally specify the source of the error at a child
+     * of the current expression at `this.key`.
+     * @private
+     */
+    error(error: string, ...keys: Array<number>) {
+        const key = `${this.key}${keys.map(k => `[${k}]`).join('')}`;
+        this.errors.push(new ParsingError(key, error));
+    }
+
+    /**
+     * Returns null if `t` is a subtype of `expected`; otherwise returns an
+     * error message and also pushes it to `this.errors`.
+     */
+    checkSubtype(expected: Type, t: Type): ?string {
+        const error = checkSubtype(expected, t);
+        if (error) this.error(error);
+        return error;
+    }
+}
+
+export default ParsingContext;
+
+function isConstant(expression: Expression) {
+    if (expression instanceof Var) {
+        return isConstant(expression.boundExpression);
+    } else if (expression instanceof CompoundExpression && expression.name === 'error') {
+        return false;
+    } else if (expression instanceof CollatorExpression) {
+        // Although the results of a Collator expression with fixed arguments
+        // generally shouldn't change between executions, we can't serialize them
+        // as constant expressions because results change based on environment.
+        return false;
+    } else if (expression instanceof Within) {
+        return false;
+    }
+
+    const isTypeAnnotation = expression instanceof Coercion ||
+        expression instanceof Assertion;
+
+    let childrenConstant = true;
+    expression.eachChild(child => {
+        // We can _almost_ assume that if `expressions` children are constant,
+        // they would already have been evaluated to Literal values when they
+        // were parsed.  Type annotations are the exception, because they might
+        // have been inferred and added after a child was parsed.
+
+        // So we recurse into isConstant() for the children of type annotations,
+        // but otherwise simply check whether they are Literals.
+        if (isTypeAnnotation) {
+            childrenConstant = childrenConstant && isConstant(child);
+        } else {
+            childrenConstant = childrenConstant && child instanceof Literal;
+        }
+    });
+    if (!childrenConstant) {
+        return false;
+    }
+
+    return isFeatureConstant(expression) &&
+        isGlobalPropertyConstant(expression, ['zoom', 'heatmap-density', 'line-progress', 'sky-radial-progress', 'accumulated', 'is-supported-script', 'pitch', 'distance-from-center']);
+}