Collapse duplicated module requires

[evmar]

import {A} from './foo';
import {B} from './foo';

A, B;

becomes

var foo_1 = require('./foo');
var foo_2 = require('./foo');
foo_1.A, foo_2.B;

We need to collapse those multiple requires into

var foo_1 = require('./foo');
var foo_2 = foo_1;

(This is not just a thing that can be handled by the user by just avoiding double imports, because if you'll get the duplicate identifiers also if you import and export from the same module.)

[evmar]

Part of issue #111.

[alexeagle]

note, everything I've tried here is very slow (like >5m to compile angular2)
so I'm not sending a PR from https://github.com/angular/sickle/tree/ajd

It seems like even with hash-based map lookup, it is too expensive to check every import statement against the previously seen ones. If the imports were known to be ordered by clang-format, then we would be able to do this in O(1). Do you have any ideas?

[evmar]

It can't be that expensive, are you sure it's your code? Perhaps your code is just enabling compilation to make more progress and something after it is making this slow? A given file has at most ~50 imports, and even using an array it's only 50^2 = 2500 steps which should be a fraction of a second.

[alexeagle]

I'm pretty sure this change causes it. In a clean client I can build
angular2 and deps in under 2m, but it's over 5m in the client with the
sickle change.

On Mon, Apr 4, 2016 at 3:15 PM Evan Martin [email protected] wrote:

It can't be that expensive, are you sure it's your code? Perhaps your code
is just enabling compilation to make more progress and something after it
is making this slow? A given file has at most ~50 imports, and even using
an array it's only 50^2 = 2500 steps which should be a fraction of a second.

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