Remove unused catch binding #6048

MarckK · 2017-08-03T08:36:08Z

Q	A
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	yes
Deprecations?
Spec Compliancy?
Tests Added/Pass?
Fixed Tickets
License	MIT
Doc PR
Dependency Changes

codemod to remove unused catch binding

hzoo · 2017-08-03T12:23:54Z

Awesome (regarding where this goes, making the PR wherever is fine), I was almost thinking maybe each proposal should include the codemod version of itself too, but then I guess it would be hard to use since you need a cli... So maybe it would be better (later) as part of another tool like lebab/babel-update.

jridgewell · 2017-08-04T16:56:01Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+          !path.scope.getOwnBinding(path.node.param.name).referenced
+        ) {
+          const paramPath = path.get("param");
+          paramPath.remove();


So there's one more test case we need to fix:

try { } catch (e) { e = new TypeError('explain'); }

xtuc · 2017-08-06T16:37:40Z

That's awesome, thanks.

I think we should also expose some sort of standalone executable. What do you think about that?

jridgewell · 2017-08-09T17:31:02Z

...t/fixtures/remove-unused-catch-binding/try-catch-block-unused-binding-new-variable/actual.js

+try {
+  throw 0;
+} catch (e) {
+  let e = new TypeError('New variable declaration, initialization, and assignment; the catch binding is not being referenced and can be removed.');


This is actually a runtime error.

Yeah. This is fixed in #5980 . and that let e will throw an error now. Can you rebase your branch to 7.0?

jridgewell · 2017-08-09T17:31:27Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+      CatchClause(path) {
+        const binding = path.scope.getOwnBinding(path.node.param.name);
+        if (
+          binding.constantViolations.filter(el => {


Why are we filtering?

boopathi · 2017-08-09T17:58:21Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+        if (
+          path.node.param &&
+          !binding.referenced &&
+          path.scope.hasBinding(path.node.param.name)


I think this is not required here. binding is already defined, and path.scope.hasBinding is going to return true always. Did you face any issues without this check?

boopathi · 2017-08-09T18:00:25Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+
+    visitor: {
+      CatchClause(path) {
+        const binding = path.scope.getOwnBinding(path.node.param.name);


The binding can be null.

If the actual.js is

try {} catch {}

There is no param, and it'll throw when using binding.something. Can you also add a test case where the catch param is not present.

babel-bot · 2017-08-23T16:07:30Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/4865/

babel-bot · 2017-08-23T16:07:30Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/4692/

jridgewell · 2017-08-23T17:12:47Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+        if (path.node.param === null) {
+          return;
+        }
+        const binding = path.scope.getOwnBinding(path.node.param.name);


param can be a Pattern, too, so we an only match if it's an Identifier.

jridgewell · 2017-08-23T17:13:15Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+        }
+        const binding = path.scope.getOwnBinding(path.node.param.name);
+        if (
+          binding.constantViolations.filter(el => {


Do we really need to filter at all?

jridgewell · 2017-08-23T17:13:36Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+        ) {
+          return;
+        }
+        if (path.node.param && !binding.referenced) {


path.node.param has already been checked above.

jridgewell

Getting very close.

jridgewell · 2017-09-01T03:39:24Z

packages/babel-plugin-transform-remove-unused-catch-binding/src/index.js

+        if (path.node.param === null) {
+          return;
+        }
+        if (t.isObjectPattern(path.node.param)) {


If it's a pattern, we can just skip this as too much work.

So, I had previously checked if the param was an identifier and if not exited early--is this what you mean, simply exit early if param not an identifier? (Also: thank you for your code reviews!)

Yup. We could check all the binding identifiers inside a pattern, but that feels like too much work since the usual pattern is just try {} catch(e) {}

OK, done. Happy to take on any more advice :-)

…Error (not passing)

…ned a new value

…variable declaration

… now passing Took out the pass in visitor when param not an Identifier, wrote case to handle when param isObjectPattern, and wrote failing tests for when param isArrayPattern

hzoo

code itself looks good, just was thinking about how we want to publish this/users to consume - we can always change it after merge too. Not sure it should be a part of the packages/* - maybe we should move to a codemods/ folder? Ideally, users would just use a npx command to use it, and ultimately lebab would be the tool to do so?

jridgewell · 2017-09-18T18:24:31Z

Agree on moving this into a separate folder.

hzoo · 2017-09-18T19:23:02Z

Not sure on the name of the folder but codemods sounds fine for now. We can just name it babel-plugin-codemod-optional-catch-binding then?

hzoo · 2017-09-19T19:38:44Z

Nice work @MarckK, going to rename the folder!

hzoo mentioned this pull request Aug 3, 2017

Rewriting Lebab as a Babel transformer? lebab/lebab#138

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MarckK force-pushed the remove-unused-catch-binding branch from c6dba28 to 7663e57 Compare August 4, 2017 14:31

MarckK changed the title ~~[WIP] Remove unused catch binding~~ Remove unused catch binding Aug 4, 2017

jridgewell requested changes Aug 4, 2017

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MarckK force-pushed the remove-unused-catch-binding branch from 93d2cc9 to 4902b39 Compare August 8, 2017 12:48

MarckK changed the title ~~Remove unused catch binding~~ [WIP]Remove unused catch binding Aug 8, 2017

MarckK force-pushed the remove-unused-catch-binding branch 2 times, most recently from f0de374 to 2b5b252 Compare August 8, 2017 15:20

MarckK changed the title ~~[WIP]Remove unused catch binding~~ Remove unused catch binding Aug 8, 2017

MarckK force-pushed the remove-unused-catch-binding branch from e64ebab to 4e0ec2c Compare August 9, 2017 10:46

existentialism added the PR: New Feature 🚀 A type of pull request used for our changelog categories label Aug 9, 2017

jridgewell reviewed Aug 9, 2017

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boopathi reviewed Aug 9, 2017

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MarckK force-pushed the remove-unused-catch-binding branch from 4e0ec2c to a431d15 Compare August 15, 2017 20:35

MarckK force-pushed the remove-unused-catch-binding branch from a431d15 to 87a6fbb Compare August 23, 2017 15:59

jridgewell reviewed Aug 23, 2017

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MarckK force-pushed the remove-unused-catch-binding branch 2 times, most recently from 4ac05c5 to b5ea732 Compare August 31, 2017 09:59

danez closed this Aug 31, 2017

danez reopened this Aug 31, 2017

danez changed the base branch from 7.0 to master August 31, 2017 17:01

jridgewell reviewed Sep 1, 2017

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MarckK force-pushed the remove-unused-catch-binding branch from b5ea732 to 6d37b4a Compare September 3, 2017 18:15

MarckK added 2 commits September 11, 2017 17:29

outline of plugin to remove unused catch binding, test not passing

867097e

plugin to remove unused catch binding

442094f

MarckK added 13 commits September 11, 2017 17:29

Edit README.md and package.json

9216b15

tests for try catch finally

7f884e5

Add test to handle case when binding is referenced and given new Type…

24a0121

…Error (not passing)

Fix visitor to not remove catch clause param when binding being assig…

e717c9e

…ned a new value

Improve naming of tests and explanations

8cc2e97

add test case for catch param not present and fix test for duplicate …

790185d

…variable declaration

Remove binding.constantViolations filter in visitor as superfluous

32577c9

Remove duplicate check that catch clause param present

531d503

Alter visitor so returns out when catch binding is not an Identifier

0324387

Created failing tests for ObjectPattern params and rewrote visitor so…

f8e9b9b

… now passing Took out the pass in visitor when param not an Identifier, wrote case to handle when param isObjectPattern, and wrote failing tests for when param isArrayPattern

Handle case when param isArrayPattern, tests passing

9df6c6d

Update package.json to v7.0.0-alpha.20

7d37c88

Revert visitor to only consider transform if param is Identifier

fd5dc18

MarckK force-pushed the remove-unused-catch-binding branch from 6d37b4a to fd5dc18 Compare September 11, 2017 16:29

jridgewell approved these changes Sep 14, 2017

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hzoo approved these changes Sep 14, 2017

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hzoo merged commit 8dffbf1 into babel:master Sep 19, 2017

MarckK deleted the remove-unused-catch-binding branch September 20, 2017 10:59

lock bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Oct 5, 2019

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Remove unused catch binding #6048

Remove unused catch binding #6048

MarckK commented Aug 3, 2017

hzoo commented Aug 3, 2017

jridgewell Aug 4, 2017

xtuc commented Aug 6, 2017

jridgewell Aug 9, 2017

boopathi Aug 9, 2017

jridgewell Aug 9, 2017

boopathi Aug 9, 2017

boopathi Aug 9, 2017

babel-bot commented Aug 23, 2017 •

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hzoo commented Sep 19, 2017

Remove unused catch binding #6048

Remove unused catch binding #6048

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