console,util: avoid pair array generation in C++ #20831

addaleax · 2018-05-18T23:44:59Z

Use a plain [key, value, key, value]-style list instead
of an array of pairs for inspecting collections.

This also fixes a bug with console.table() where
inspecting a non-key-value MapIterator would have
led to odd results.

Refs: #20719 (comment)

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
tests and/or benchmarks are included
commit message follows commit guidelines

Use a plain `[key, value, key, value]`-style list instead of an array of pairs for inspecting collections. This also fixes a bug with `console.table()` where inspecting a non-key-value `MapIterator` would have led to odd results. Refs: nodejs#20719 (comment)

BridgeAR · 2018-05-18T23:47:54Z

lib/util.js

+  for (let i = 0; i < ret.length; ++i)
+    ret[i] = [list[2 * i], list[2 * i + 1]];
+  return ret;
+}


We could use the same pattern as in weak maps instead of first zipping this. This step is just overhead (even though the result is nicer to read).

Yes, but it gets pretty tricky to do that, at least for me… we are passing the individual pair arrays to formatValue, and it’s not obvious how/whether to short-circuit around that

(Extreme edge case: Calling formatValue() on the individual keys/values rather than the pairs even makes a difference in depth…)

I am not sure in what way this should have any influence on the depth?

BridgeAR · 2018-05-18T23:49:57Z

src/node_util.cc

+  ret->Set(env->context(), 0, entries).FromJust();
+  ret->Set(env->context(), 1, v8::Boolean::New(env->isolate(), is_key_value))
+      .FromJust();
+  return args.GetReturnValue().Set(ret);


We do not need the information about the key value pairs as we already have that when calling this function. The JS side has to be adjusted to the way it worked before to accomplish that.

We do not need the information about the key value pairs as we already have that when calling this function.

Not for Map iterators, and I’m not aware of how we could know that in advance.

The way this was done before in JS allowed this. We just pretty much have to revert the JS changes from the former PR.

@BridgeAR Not really? When we had the V8 builtins available, we could only tell them apart because some Map iterators gave us pairs and others didn’t, but if we want to avoid pair creation, then we need this.

Concrete example: This is necessary to distinguish new Map([[1,2],[3,4]]).entries() from new Map([['a',1],['b',2],['c',3],['d',4]]).values()

Thanks! I did not think about new Map().entries() anymore. However, this is only necessary in case of map iterators. So we could tell C++ if we want the return value to be wrapped in a extra array for the map iterators and just directly return the array for all set iterators.

Hm, I just checked https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/entries and now I remember why the return value for entries with a set iterator was actually so weird. That was indeed by design. I am a bit on the edge to follow that or not... As far as I know, we can not detect that anymore, right?

As far as I know, we can not detect that anymore, right?

Yes. If it helps, our behaviour is aligned with Chromium’s now (for that reason), and I think that either can be seen as valid.

BridgeAR · 2018-05-18T23:56:25Z

lib/console.js


-  const setlike = setIter || isSet(tabularData);
+  const setlike = setIter || (mapIter && !isKeyValue) || isSet(tabularData);


I am not a fan of this solution. What we should do is to detect the actual type of the tabularData before ever overriding that variable. I would just use a second variable to make this easier. As in:

let data = tabularData; if (mapIter) { ... }

I’m not sure I understand this comment… Second argument to which function exactly?

Sorry, second variable (not argument).

The reason for the issue is that the type can not be properly detected anymore after overriding the original input. So we need a reference to the original input that we never override and one that could potentially be changed. That way the implementation should be easier. I guess I should not have accepted the PR to be landed originally :/

If you want, I can take a stab at this.

I mean, we did override tabularData before too, so this isn’t really a step back on that (if that’s the variable you’re referring to).

Tbh, I’m still not really getting what you’re trying to say, but it might just be easier to talk about concrete code, yes. :)

That way the implementation should be easier. I guess I should not have accepted the PR to be landed originally :/

Are you talking about #20719 or the one that introduced the table code in the first place? The former one did not make any changes to this code that go beyond trivial…

I mean the original table code in the first place.

I am to tired tonight but I am going to have a look at it tomorrow. Is it fine to just push to your branch directly?

Yeah, feel free to do that. :)

After looking into this closer it does indeed require some deeper changes for what I thought about.

TimothyGu

LGTM in general. Some minor comments.

TimothyGu · 2018-05-19T00:45:36Z

lib/console.js

  if (mapIter)
-    tabularData = previewEntries(tabularData);
+    [ tabularData, isKeyValue ] = previewEntries(tabularData);


The syntax makes me go 😬

Let's make it

if (mapIter) { ;([tabularData, isKeyValue] = previewEntries(tabularData)); }

that leading semi isn't really node style, but i agree to brackets + wrapping in parens

TimothyGu · 2018-05-19T00:49:41Z

lib/console.js

@@ -367,9 +376,9 @@ Console.prototype.table = function(tabularData, properties) {

  const setIter = isSetIterator(tabularData);
  if (setIter)
-    tabularData = previewEntries(tabularData);
+    [ tabularData ] = previewEntries(tabularData);


Can we make it previewEntries(tabularData)[0] instead?

TimothyGu · 2018-05-19T00:52:10Z

lib/util.js

-  const entries = previewEntries(value).slice(0, maxArrayLength + 1);
-  const remainder = entries.length > maxArrayLength;
-  const len = entries.length - (remainder ? 1 : 0);
+  const [ entries ] = previewEntries(value).slice(0, (maxArrayLength + 1) * 2);


nit: we don't usually put spaces inside of []. [entries] is fine.

The slice is actually unnecessary overhead. The limitation is done below and this has no effect (there are just two entries returned).

TimothyGu · 2018-05-19T00:54:27Z

test/parallel/test-util-inspect.js

@@ -447,13 +447,13 @@ assert.strictEqual(util.inspect(-5e-324), '-5e-324');
 {
  const map = new Map();
  map.set(1, 2);
-  const vals = previewEntries(map.entries());
+  const [ vals ] = previewEntries(map.entries());


Might be a good idea for us to test isKeyValue as well.

devsnek

i couldn't find anything to nitpick so with the other comments handled this lgtm

addaleax · 2018-05-23T15:55:24Z

@BridgeAR I wanted to wait for you to push changes you’d like to see before I continue with this PR … where are you at regarding that? Otherwise I’d probably address some of the newer comments here first

BridgeAR · 2018-05-25T10:16:28Z

@addaleax I have my local change ready but it became somewhat more involved, so I decided to just open a PR on top of this one. I am going to rebase when this PR lands.

BridgeAR · 2018-06-25T00:34:01Z

@addaleax did you have a look at my follow up PR? :-)

BridgeAR · 2018-07-15T00:35:08Z

CI https://ci.nodejs.org/job/node-test-pull-request/15880/

Use a plain `[key, value, key, value]`-style list instead of an array of pairs for inspecting collections. This also fixes a bug with `console.table()` where inspecting a non-key-value `MapIterator` would have led to odd results. PR-URL: nodejs#20831 Refs: nodejs#20719 (comment) Reviewed-By: Tiancheng "Timothy" Gu <[email protected]> Reviewed-By: Gus Caplan <[email protected]> Reviewed-By: Minwoo Jung <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Ruben Bridgewater <[email protected]>

BridgeAR · 2018-07-16T08:53:53Z

Landed in db49589.

I fixed the eslint errors while landing.

Use a plain `[key, value, key, value]`-style list instead of an array of pairs for inspecting collections. This also fixes a bug with `console.table()` where inspecting a non-key-value `MapIterator` would have led to odd results. PR-URL: #20831 Refs: #20719 (comment) Reviewed-By: Tiancheng "Timothy" Gu <[email protected]> Reviewed-By: Gus Caplan <[email protected]> Reviewed-By: Minwoo Jung <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Ruben Bridgewater <[email protected]>

addaleax added util Issues and PRs related to the built-in util module. console Issues and PRs related to the console subsystem. labels May 18, 2018

addaleax requested review from devsnek and BridgeAR May 18, 2018 23:44

nodejs-github-bot added the lib / src Issues and PRs related to general changes in the lib or src directory. label May 18, 2018

addaleax force-pushed the preview-entries-2 branch from a6150b1 to c90c676 Compare May 18, 2018 23:45

BridgeAR reviewed May 18, 2018

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TimothyGu approved these changes May 19, 2018

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devsnek approved these changes May 19, 2018

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JungMinu approved these changes May 20, 2018

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jasnell approved these changes May 23, 2018

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BridgeAR mentioned this pull request May 25, 2018

util: improve display of iterators and weak entries #20961

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BridgeAR added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Jul 14, 2018

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BridgeAR closed this Jul 16, 2018

targos mentioned this pull request Jul 17, 2018

v10.7.0 proposal #21851

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BridgeAR mentioned this pull request Nov 25, 2018

Incorrect inspection of Set iterator for set.entries() #24629

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console,util: avoid pair array generation in C++ #20831

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		const setlike = setIter \|\| isSet(tabularData);
		const setlike = setIter \|\| (mapIter && !isKeyValue) \|\| isSet(tabularData);

console,util: avoid pair array generation in C++ #20831

console,util: avoid pair array generation in C++ #20831

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addaleax commented May 18, 2018

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