From be75fe90afb004e2c8c873123fba0782cb2e471a Mon Sep 17 00:00:00 2001
From: Chris Loer <chris.loer@gmail.com>
Date: Wed, 18 Jul 2018 10:55:54 -0700
Subject: [PATCH] Support implicit argument coercions for compound expressions
 with multiple overloads. Support string->formatted coercion (currently
 unused).

---
 .../expression/compound_expression.js         | 53 ++++++++++++-------
 .../expression/definitions/coercion.js        | 10 ++++
 src/style-spec/expression/parsing_context.js  |  4 ++
 3 files changed, 47 insertions(+), 20 deletions(-)

diff --git a/src/style-spec/expression/compound_expression.js b/src/style-spec/expression/compound_expression.js
index e5417f1c6bf..d9dd2b7223d 100644
--- a/src/style-spec/expression/compound_expression.js
+++ b/src/style-spec/expression/compound_expression.js
@@ -67,22 +67,6 @@ class CompoundExpression implements Expression {
             signature.length === args.length - 1 // correct param count
         ));
 
-        // First parse all the args
-        const parsedArgs: Array<Expression> = [];
-        for (let i = 1; i < args.length; i++) {
-            const arg = args[i];
-            let expected;
-            if (overloads.length === 1) {
-                const params = overloads[0][0];
-                expected = Array.isArray(params) ?
-                    params[i - 1] :
-                    params.type;
-            }
-            const parsed = context.parse(arg, 1 + parsedArgs.length, expected);
-            if (!parsed) return null;
-            parsedArgs.push(parsed);
-        }
-
         let signatureContext: ParsingContext = (null: any);
 
         for (const [params, evaluate] of overloads) {
@@ -90,6 +74,29 @@ class CompoundExpression implements Expression {
             // we eventually succeed, we haven't polluted `context.errors`.
             signatureContext = new ParsingContext(context.registry, context.path, null, context.scope);
 
+            // First parse all the args, potentially coercing to the
+            // types expected by this overload.
+            const parsedArgs: Array<Expression> = [];
+            let argParseFailed = false;
+            for (let i = 1; i < args.length; i++) {
+                const arg = args[i];
+                const expectedType = Array.isArray(params) ?
+                    params[i - 1] :
+                    params.type;
+
+                const parsed = signatureContext.parse(arg, 1 + parsedArgs.length, expectedType);
+                if (!parsed) {
+                    argParseFailed = true;
+                    break;
+                }
+                parsedArgs.push(parsed);
+            }
+            if (argParseFailed) {
+                // Couldn't coerce args of this overload to expected type, move
+                // on to next one.
+                continue;
+            }
+
             if (Array.isArray(params)) {
                 if (params.length !== parsedArgs.length) {
                     signatureContext.error(`Expected ${params.length} arguments, but found ${parsedArgs.length} instead.`);
@@ -117,10 +124,16 @@ class CompoundExpression implements Expression {
             const signatures = expected
                 .map(([params]) => stringifySignature(params))
                 .join(' | ');
-            const actualTypes = parsedArgs
-                .map(arg => toString(arg.type))
-                .join(', ');
-            context.error(`Expected arguments of type ${signatures}, but found (${actualTypes}) instead.`);
+
+            const actualTypes = [];
+            // For error message, re-parse arguments without trying to
+            // apply any coercions
+            for (let i = 1; i < args.length; i++) {
+                const parsed = context.parse(args[i], 1 + actualTypes.length);
+                if (!parsed) return null;
+                actualTypes.push(toString(parsed.type));
+            }
+            context.error(`Expected arguments of type ${signatures}, but found (${actualTypes.join(', ')}) instead.`);
         }
 
         return null;
diff --git a/src/style-spec/expression/definitions/coercion.js b/src/style-spec/expression/definitions/coercion.js
index ba50f63aee4..59fcbef4e2b 100644
--- a/src/style-spec/expression/definitions/coercion.js
+++ b/src/style-spec/expression/definitions/coercion.js
@@ -10,6 +10,7 @@ import type { Expression } from '../expression';
 import type ParsingContext from '../parsing_context';
 import type EvaluationContext from '../evaluation_context';
 import type { Type } from '../types';
+import { Formatted, FormattedSection } from './formatted';
 
 const types = {
     'to-number': NumberType,
@@ -73,6 +74,15 @@ class Coercion implements Expression {
                 }
             }
             throw new RuntimeError(error || `Could not parse color from value '${typeof input === 'string' ? input : JSON.stringify(input)}'`);
+        } else if (this.type.kind === 'formatted') {
+            let input;
+            for (const arg of this.args) {
+                input = arg.evaluate(ctx);
+                if (typeof input === 'string') {
+                    return new Formatted([new FormattedSection(input, null, null)]);
+                }
+            }
+            throw new RuntimeError(`Could not parse formatted text from value '${typeof input === 'string' ? input : JSON.stringify(input)}'`);
         } else {
             let value = null;
             for (const arg of this.args) {
diff --git a/src/style-spec/expression/parsing_context.js b/src/style-spec/expression/parsing_context.js
index 1ce14898323..5e4d1a51e21 100644
--- a/src/style-spec/expression/parsing_context.js
+++ b/src/style-spec/expression/parsing_context.js
@@ -113,6 +113,10 @@ class ParsingContext {
                         if (!options.omitTypeAnnotations) {
                             parsed = new Coercion(expected, [parsed]);
                         }
+                    } else if (expected.kind === 'formatted' && (actual.kind === 'value' || actual.kind === 'string')) {
+                        if (!options.omitTypeAnnotations) {
+                            parsed = new Coercion(expected, [parsed]);
+                        }
                     } else if (this.checkSubtype(this.expectedType, parsed.type)) {
                         return null;
                     }