Add error context

Also eliminate outdated dictionary error for Date and RegExp.

lib/constructs/attribute.js

@@ -54,7 +54,7 @@ Attribute.prototype.generate = function () {
     ${getterBody}
   },`;
   if (!this.idl.readonly) {
-    const conv = Types.generateTypeConversion(this.ctx, "V", this.idl.idlType, this.idl.extAttrs, this.interface.name);
+    const conv = Types.generateTypeConversion(this.ctx, "V", this.idl.idlType, this.idl.extAttrs, this.interface.name, `"Failed to set the '${this.idl.name}' property on '${this.interface.name}': The provided value"`);
     Object.assign(requires, conv.requires);
     let conversion = conv.body.replace(/\n/g, "\n  ");
     str += `

lib/constructs/dictionary.js

@@ -33,7 +33,7 @@ class Dictionary {
     if (value !== undefined) {`;
       const argAttrs = field.extAttrs;
 
-      const conv = Types.generateTypeConversion(this.ctx, "value", typeConversion, argAttrs, this.name);
+      const conv = Types.generateTypeConversion(this.ctx, "value", typeConversion, argAttrs, this.name, `\`\${context} has member ${field.name} that\``);
       for (let key in conv.requires) {
         this.str = `const ${key} = ${conv.requires[key]};\n` + this.str;
       }
@@ -63,26 +63,23 @@ class Dictionary {
   generate() {
     this.str += `
 module.exports = {
-  convertInherit(obj, ret) {`;
+  convertInherit(obj, ret, { context = "The provided value" } = {}) {`;
     if (this.idl.inheritance) {
       this.str = `const ${this.idl.inheritance} = require("./${this.idl.inheritance}");\n` + this.str;
       this.str += `
-    ${this.idl.inheritance}.convertInherit(obj, ret);`;
+    ${this.idl.inheritance}.convertInherit(obj, ret, { context });`;
     }
     this._generateConversions();
     this.str += `
   },
 
-  convert(obj) {
+  convert(obj, { context = "The provided value" } = {}) {
     if (obj !== undefined && typeof obj !== "object") {
-      throw new TypeError("Dictionary has to be an object");
-    }
-    if (obj instanceof Date || obj instanceof RegExp) {
-      throw new TypeError("Dictionary may not be a Date or RegExp object");
+      throw new TypeError(\`\${context} is not an object.\`);
     }
 
     const ret = Object.create(null);
-    module.exports.convertInherit(obj, ret);
+    module.exports.convertInherit(obj, ret, { context });
     return ret;
   }
 };`;

lib/constructs/interface.js

@@ -91,7 +91,7 @@ Interface.prototype.generateConstructor = function () {
       }
     }
 
-    const conversions = Parameters.generateOverloadConversions(this.ctx, overloads, this.name);
+    const conversions = Parameters.generateOverloadConversions(this.ctx, overloads, this.name, `Failed to construct '${this.name}': `);
     Object.assign(this.requires, conversions.requires);
 
     minConstructor.nameList = minConstructor.nameList.map((name) => (keywords.has(name) ? "_" : "") + name);
@@ -187,11 +187,11 @@ Interface.prototype.generateExport = function () {
     }
     return false;
   },
-  convert(obj) {
+  convert(obj, { context = "The provided value" } = {}) {
     if (module.exports.is(obj)) {
       return utils.implForWrapper(obj);
     }
-    throw new TypeError("The value provided is not a ${this.name}");
+    throw new TypeError(\`\${context} is not of type '${this.name}'.\`);
   },`;
 
   if (this.iterable) {

lib/constructs/operation.js

@@ -53,7 +53,7 @@ Operation.prototype.generate = function () {
 
   const callOn = this.idl.static ? "Impl" : "this[impl]";
 
-  const parameterConversions = Parameters.generateOverloadConversions(this.ctx, overloads, this.interface.name);
+  const parameterConversions = Parameters.generateOverloadConversions(this.ctx, overloads, this.interface.name, `Failed to execute '${name}' on '${this.obj.name}': `);
   const argsSpread = parameterConversions.hasArgs ? "...args" : "";
   Object.assign(requires, parameterConversions.requires);
   str += parameterConversions.body;

lib/parameters.js

@@ -22,7 +22,7 @@ function getDefault(dflt) {
   throw new Error("Unexpected default type: " + dflt.type);
 }
 
-function generateVarConversion(ctx, name, conversion, argAttrs, parentName) {
+function generateVarConversion(ctx, name, conversion, argAttrs, ...typeArgs) {
   const { customTypes } = ctx;
   const requires = {};
   let str = "";
@@ -33,7 +33,7 @@ function generateVarConversion(ctx, name, conversion, argAttrs, parentName) {
 if (${name} !== undefined) {`;
   }
 
-  const conv = Types.generateTypeConversion(ctx, name, idlType, argAttrs, parentName);
+  const conv = Types.generateTypeConversion(ctx, name, idlType, argAttrs, ...typeArgs);
   Object.assign(requires, conv.requires);
   str += conv.body;
 
@@ -53,7 +53,7 @@ if (${name} !== undefined) {`;
   };
 };
 
-module.exports.generateOverloadConversions = function (ctx, overloads, parentName) {
+module.exports.generateOverloadConversions = function (ctx, overloads, parentName, errPrefix) {
   const { customTypes } = ctx;
   const requires = {};
   let str = ``;
@@ -89,7 +89,7 @@ module.exports.generateOverloadConversions = function (ctx, overloads, parentNam
         continue;
       }
 
-      const conv = generateVarConversion(ctx, `args[${i}]`, typeConversions[i], maxConstructor.operation.arguments[i].extAttrs, parentName);
+      const conv = generateVarConversion(ctx, `args[${i}]`, typeConversions[i], maxConstructor.operation.arguments[i].extAttrs, parentName, `"${errPrefix}parameter ${i + 1}"`);
       Object.assign(requires, conv.requires);
       str += conv.body;
     }

lib/types.js

@@ -4,7 +4,7 @@ const conversions = require("webidl-conversions");
 
 const utils = require("./utils");
 
-function generateTypeConversion(ctx, name, idlType, argAttrs, parentName) {
+function generateTypeConversion(ctx, name, idlType, argAttrs, parentName, errPrefix = '"The provided value"') {
   const { customTypes } = ctx;
   const requires = {};
   let str = "";
@@ -62,13 +62,13 @@ function generateTypeConversion(ctx, name, idlType, argAttrs, parentName) {
   function generateSequence() {
     str += `
   if (typeof ${name} !== "object") {
-    throw new TypeError("The value provided is not an iterable object");
+    throw new TypeError(${errPrefix} + " is not an iterable object.");
   } else {
     const V = [];
     const tmp = ${name};
     for (let nextItem of tmp) {`;
 
-    const conv = generateTypeConversion(ctx, "nextItem", idlType.idlType, [], parentName);
+    const conv = generateTypeConversion(ctx, "nextItem", idlType.idlType, [], parentName, errPrefix);
     Object.assign(requires, conv.requires);
     str += conv.body;
 
@@ -89,7 +89,7 @@ function generateTypeConversion(ctx, name, idlType, argAttrs, parentName) {
 
     str += `
   if (typeof ${name} !== "object") {
-    throw new TypeError("The value provided is not an object");
+    throw new TypeError(${errPrefix} + " is not an object.");
   } else {
     const result = Object.create(null);
     const keys = Object.getOwnPropertyNames(${name});
@@ -100,9 +100,9 @@ function generateTypeConversion(ctx, name, idlType, argAttrs, parentName) {
         let typedKey = key;
         let typedValue = value;`;
 
-    str += generateTypeConversion(ctx, "typedKey", idlType.idlType[0], [], parentName).body;
+    str += generateTypeConversion(ctx, "typedKey", idlType.idlType[0], [], parentName, errPrefix).body;
 
-    const conv = generateTypeConversion(ctx, "typedValue", idlType.idlType[1], [], parentName);
+    const conv = generateTypeConversion(ctx, "typedValue", idlType.idlType[1], [], parentName, errPrefix);
     Object.assign(requires, conv.requires);
     str += conv.body;
 
@@ -135,14 +135,15 @@ function generateTypeConversion(ctx, name, idlType, argAttrs, parentName) {
     const clamp = utils.getExtAttr(argAttrs, "Clamp");
     const treatNullAs = utils.getExtAttr(argAttrs, "TreatNullAs");
 
-    let optString = "";
+    let optString = `, { context: ${errPrefix}`;
     if (clamp) {
-      optString = `, { clamp: true }`;
+      optString += ", clamp: true";
     } else if (enforceRange) {
-      optString = `, { enforceRange: true }`;
+      optString += ", enforceRange: true";
     } else if (treatNullAs && treatNullAs.rhs.value === "EmptyString") {
-      optString = `, { treatNullAsEmptyString: true }`;
+      optString += ", treatNullAsEmptyString: true";
     }
+    optString += " }";
     if (idlType.array) {
       str += `
   for (let i = 0; i < ${name}.length; ++i) {