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Hoist await and yield #6

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Hoist await and yield #6

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43 changes: 42 additions & 1 deletion index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,8 @@ var buildHelper = template([
'}'
].join('\n'));

var hoistExpression = template('var ARG = EXP;');

var assertionVisitor = {
CallExpression: function (path, state) {
if (isThrowsMember(path.get('callee'))) {
Expand All @@ -40,14 +42,24 @@ var assertionVisitor = {
return;
}

var hoisted = hoistAwaitAndYield(path, arg0);

path.node.arguments[0] = wrapWithHelper({
HELPER_ID: t.identifier(this.avaThrowHelper()),
EXP: arg0,
EXP: hoisted ? hoisted.arg0 : 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;

if (hoisted) {
path.replaceWithMultiple(
hoisted.expressions.concat(
t.expressionStatement(path.node)
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You are replacing the Callxpression by an ExpressionStatement here. Would the following test code stll work, or would Babel crash or something because you are building an odd AST?

test('should foo...', async t => {
  t.is(
      t.throws(foo(await quux())).message,
     'Could not find X'
   );
});

My worry is that you can't AFAIK pass a statement as the argument of a function (here, the `t.is(){ call). But I don't know how Babel would react to that. Would you mind adding a test case and see how that pans out?
I would be fine with not entirely supporting this edge case, but it should at the very least not crash.

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Yea I doubt that'll work… in your example t.throws is inside an ArgumentExpression so we'd have to walk the path back to the test implementation and detect any ArgumentExpression nodes, then prepend the hosted statements to node's parent.

But then what about:

test(async t => {
  (function* () {
    const err = await t.throws(foo(yield))
    t.true(err.message === 'hahaha')
  })()
})

That scenario is further complicated by this plugin running after async/await has been transpiled into a generator…

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So, what should we do about it? Just ignore it as an edge-case?

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I haven't had the time to get back to this. We could explore whether we can run this plugin before any other presets and plugins. Alternatively the generator compilation (for Node.js v4 and up) should reduce to yield expressions.

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@sindresorhus sindresorhus Nov 5, 2016 •
edited
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Relevant: babel/babel#3281

Alternatively the generator compilation (for Node.js v4 and up) should reduce to yield expressions.

I would be ok with only supporting Node.js 4 for this.

)
);
}
}
}
};
Expand Down Expand Up @@ -83,3 +95,32 @@ function isThrowsMember(path) {
path.get('property').isIdentifier({name: 'notThrows'})
);
}

function hoistAwaitAndYield(path, arg0) {
if (t.isAwaitExpression(arg0) || t.isYieldExpression(arg0)) {
var arg = path.scope.generateUidIdentifier('arg');
return {
expressions: [hoistExpression({ARG: arg, EXP: arg0})],
arg0: arg
};
}

if (t.isCallExpression(arg0)) {
var expressions = [];
arg0.arguments = arg0.arguments.map(function (arg) {
var hoisted = hoistAwaitAndYield(path, arg);
if (!hoisted) {
return arg;
}

expressions = expressions.concat(hoisted.expressions);
return hoisted.arg0;
});
return {
expressions: expressions,
arg0: arg0
};
}

return null;
}
64 changes: 58 additions & 6 deletions test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -51,24 +51,28 @@ const HELPER = `function _avaThrowsHelper(fn, data) {
}
}\n`;

function wrapped(throws, expression, line, column) {
function wrapped(throws, line, column, expression, source = expression) { // eslint-disable-line max-params
return `t.${throws}(_avaThrowsHelper(function () {
return ${expression};
}, {
line: ${line},
column: ${column},
source: "${expression}",
source: "${source}",
filename: "some-file.js"
}));`;
}

function indent(str) {
return str.replace(/\n/g, '\n ').trimRight();
}

test('creates a helper', t => {
const input = 't.throws(foo())';
const {code} = transform(input);

const expected = [
HELPER,
wrapped('throws', 'foo()', 1, 9)
wrapped('throws', 1, 9, 'foo()')
].join('\n');

t.is(code, expected);
Expand All @@ -81,14 +85,62 @@ test('creates the helper only once', t => {

const expected = [
HELPER,
wrapped('throws', 'foo()', 1, 9),
wrapped('throws', 'bar()', 2, 9)
wrapped('throws', 1, 9, 'foo()'),
wrapped('throws', 2, 9, 'bar()')
].join('\n');

t.is(code, expected);
addExample(input, code);
});

test('hoists await expressions', t => {
const input = `async function test() {
t.throws(foo(await bar(), await baz(), qux));
t.throws(await quux);
}`;
const {code} = transform(input);

const expected = `${HELPER}
async function test() {
var _arg = await bar();

var _arg2 = await baz();

${indent(wrapped('throws', 2, 11, 'foo(_arg, _arg2, qux)', 'foo(await bar(), await baz(), qux)'))}

var _arg3 = await quux;

${indent(wrapped('throws', 3, 11, '_arg3', 'await quux'))}
}`;

t.is(code, expected);
addExample(input, code);
});

test('hoists yield expressions', t => {
const input = `function* test() {
t.throws(foo(yield bar(), yield baz(), qux));
t.throws(yield quux);
}`;
const {code} = transform(input);

const expected = `${HELPER}
function* test() {
var _arg = yield bar();

var _arg2 = yield baz();

${indent(wrapped('throws', 2, 11, 'foo(_arg, _arg2, qux)', 'foo(yield bar(), yield baz(), qux)'))}

var _arg3 = yield quux;

${indent(wrapped('throws', 3, 11, '_arg3', 'yield quux'))}
}`;

t.is(code, expected);
addExample(input, code);
});

test('does nothing if it does not match', t => {
const input = 't.is(foo());';
const {code} = transform(input);
Expand All @@ -103,7 +155,7 @@ test('helps notThrows', t => {

const expected = [
HELPER,
wrapped('notThrows', 'baz()', 1, 12)
wrapped('notThrows', 1, 12, 'baz()')
].join('\n');

t.is(code, expected);
Expand Down