Simplify implementation

Rather than trying to catch the errors, wrap the argument such that the
test knows that an exception occurred before the assertion was invoked.

Author: novemberborn

example-output.md

@@ -7,32 +7,21 @@ t.throws(foo())
 becomes:
 
 ```js
-function _avaThrowsHelper(fn, data) {
-  try {
-    return fn();
-  } catch (e) {
-    var type = typeof e;
-
-    if (e !== null && (type === "object" || type === "function")) {
-      try {
-        Object.defineProperty(e, "_avaThrowsHelperData", {
-          value: data
-        });
-      } catch (e) {}
-    }
-
-    throw e;
+function _avaThrowsHelperStart(t, assertion, file, line) {
+  if (t._throwsArgStart) {
+    t._throwsArgStart(assertion, file, line);
   }
 }
 
-t.throws(_avaThrowsHelper(function () {
-  return foo();
-}, {
-  line: 1,
-  column: 9,
-  source: "foo()",
-  filename: "some-file.js"
-}));
+function _avaThrowsHelperEnd(t, arg) {
+  if (t._throwsArgEnd) {
+    t._throwsArgEnd();
+  }
+
+  return arg;
+}
+
+t.throws((_avaThrowsHelperStart(t, "throws", "some-file.js", 1), _avaThrowsHelperEnd(t, foo())));
 ```
 
 ---
@@ -47,40 +36,22 @@ t.throws(bar());
 becomes:
 
 ```js
-function _avaThrowsHelper(fn, data) {
-  try {
-    return fn();
-  } catch (e) {
-    var type = typeof e;
-
-    if (e !== null && (type === "object" || type === "function")) {
-      try {
-        Object.defineProperty(e, "_avaThrowsHelperData", {
-          value: data
-        });
-      } catch (e) {}
-    }
-
-    throw e;
+function _avaThrowsHelperStart(t, assertion, file, line) {
+  if (t._throwsArgStart) {
+    t._throwsArgStart(assertion, file, line);
+  }
+}
+
+function _avaThrowsHelperEnd(t, arg) {
+  if (t._throwsArgEnd) {
+    t._throwsArgEnd();
   }
+
+  return arg;
 }
 
-t.throws(_avaThrowsHelper(function () {
-  return foo();
-}, {
-  line: 1,
-  column: 9,
-  source: "foo()",
-  filename: "some-file.js"
-}));
-t.throws(_avaThrowsHelper(function () {
-  return bar();
-}, {
-  line: 2,
-  column: 9,
-  source: "bar()",
-  filename: "some-file.js"
-}));
+t.throws((_avaThrowsHelperStart(t, "throws", "some-file.js", 1), _avaThrowsHelperEnd(t, foo())));
+t.throws((_avaThrowsHelperStart(t, "throws", "some-file.js", 2), _avaThrowsHelperEnd(t, bar())));
 ```
 
 ---
@@ -108,32 +79,21 @@ t.notThrows(baz())
 becomes:
 
 ```js
-function _avaThrowsHelper(fn, data) {
-  try {
-    return fn();
-  } catch (e) {
-    var type = typeof e;
-
-    if (e !== null && (type === "object" || type === "function")) {
-      try {
-        Object.defineProperty(e, "_avaThrowsHelperData", {
-          value: data
-        });
-      } catch (e) {}
-    }
-
-    throw e;
+function _avaThrowsHelperStart(t, assertion, file, line) {
+  if (t._throwsArgStart) {
+    t._throwsArgStart(assertion, file, line);
+  }
+}
+
+function _avaThrowsHelperEnd(t, arg) {
+  if (t._throwsArgEnd) {
+    t._throwsArgEnd();
   }
+
+  return arg;
 }
 
-t.notThrows(_avaThrowsHelper(function () {
-  return baz();
-}, {
-  line: 1,
-  column: 12,
-  source: "baz()",
-  filename: "some-file.js"
-}));
+t.notThrows((_avaThrowsHelperStart(t, "notThrows", "some-file.js", 1), _avaThrowsHelperEnd(t, baz())));
 ```
 
 ---

index.js

@@ -1,85 +1,70 @@
 'use strict';
-var t = require('babel-types');
-var template = require('babel-template');
 
-var wrapWithHelper = template([
-	'HELPER_ID(function () {',
-	'  return EXP;',
-	'}, {',
-	'  line: LINE,',
-	'  column: COLUMN,',
-	'  source: SOURCE,',
-	'  filename: FILE',
-	'});'
-].join('\n'));
+module.exports = babelCore => {
+	const t = babelCore.types;
+	const wrapArg = babelCore.template('(START(t, ASSERTION, FILE, LINE), END(t, ARG))');
+	const helpers = babelCore.template(`function START(t, assertion, file, line) {
+  if (t._throwsArgStart) {
+    t._throwsArgStart(assertion, file, line);
+  }
+}
+
+function END(t, arg) {
+  if (t._throwsArgEnd) {
+    t._throwsArgEnd();
+  }
 
-var buildHelper = template([
-	'function HELPER_ID(fn, data) {',
-	'  try {',
-	'    return fn();',
-	'  } catch (e) {',
-	'    var type = typeof e;',
-	'    if (e !== null && (type === "object" || type === "function")) {',
-	'      try {',
-	'        Object.defineProperty(e, "_avaThrowsHelperData", {',
-	'          value: data',
-	'        });',
-	'      } catch (e) {}',
-	'    }',
-	'    throw e;',
-	'  }',
-	'}'
-].join('\n'));
+  return arg;
+}`);
 
-var assertionVisitor = {
-	CallExpression: function (path, state) {
-		if (isThrowsMember(path.get('callee'))) {
-			var arg0 = path.node.arguments[0];
+	const assertionVisitor = {
+		CallExpression(path, state) {
+			const callee = path.get('callee');
+			if (!callee.isMemberExpression() || !callee.get('object').isIdentifier({name: 't'}) || !callee.get('property').isIdentifier()) {
+				return;
+			}
 
+			const assertion = callee.get('property').get('name').node;
+			if (assertion !== 'throws' && assertion !== 'notThrows') {
+				return;
+			}
+
+			const arg0 = path.node.arguments[0];
 			if (!(arg0 && arg0.loc && (typeof arg0.start === 'number') && (typeof arg0.end === 'number'))) {
 				return;
 			}
 
-			path.node.arguments[0] = wrapWithHelper({
-				HELPER_ID: t.identifier(this.avaThrowHelper()),
-				EXP: arg0,
-				LINE: t.numericLiteral(arg0.loc.start.line),
-				COLUMN: t.numericLiteral(arg0.loc.start.column),
-				SOURCE: t.stringLiteral(state.file.code.substring(arg0.start, arg0.end)),
-				FILE: t.stringLiteral(state.file.opts.filename)
-			}).expression;
+			// Wrap the argument expression, so that the stack trace of the assertion
+			// isn't affected.
+			path.node.arguments[0] = wrapArg(Object.assign({
+				ARG: arg0,
+				ASSERTION: t.stringLiteral(assertion),
+				FILE: t.stringLiteral(state.file.opts.filename),
+				LINE: t.numericLiteral(arg0.loc.start.line)
+			}, this.installHelper())).expression;
 		}
-	}
-};
+	};
 
-module.exports = function () {
 	return {
 		visitor: {
-			Program: function (path, state) {
-				var HELPER_ID = path.scope.generateUid('avaThrowsHelper');
-				var created = false;
+			Program(path, state) {
+				const START = t.identifier(path.scope.generateUid('avaThrowsHelperStart'));
+				const END = t.identifier(path.scope.generateUid('avaThrowsHelperEnd'));
+				const helperIdentifiers = {START, END};
 
+				let created = false;
 				path.traverse(assertionVisitor, {
-					avaThrowHelper: function () {
+					installHelper() {
 						if (!created) {
 							created = true;
-							path.unshiftContainer('body', buildHelper({
-								HELPER_ID: t.identifier(HELPER_ID)
-							}));
+							path.unshiftContainer('body', helpers(helperIdentifiers));
 						}
 
-						return HELPER_ID;
+						return helperIdentifiers;
 					},
 					file: state.file
 				});
 			}
 		}
 	};
 };
-
-function isThrowsMember(path) {
-	return path.isMemberExpression() && path.get('object').isIdentifier({name: 't'}) && (
-			path.get('property').isIdentifier({name: 'throws'}) ||
-			path.get('property').isIdentifier({name: 'notThrows'})
-		);
-}

package.json

@@ -27,10 +27,6 @@
     "assertion",
     "throws"
   ],
-  "dependencies": {
-    "babel-template": "^6.7.0",
-    "babel-types": "^6.7.2"
-  },
   "devDependencies": {
     "ava": "^0.18.2",
     "babel-core": "^6.7.5",