JavaScript: destructuring binding

[masatake]

Close #1112.

Limitations:

• If an object literal is specified as a default value in object restructuring, the parser may fail to extract the variable (or constant):

  var{ c = {a: 1} } = { c: undefined };
  var{ d = {a: 1} } = {d: 3};
  var a = 1
  var [x = {a: 2}, y] = [, 4];
  var [x = [a, 2], y] = [, 4];
  

  I will try to remove this limitation.

• key in [key] is extracted unexpectedly.

  let key = 'z';
  let {[key]: foo} = {z: 'bar'};
  

• the parser fills the signature field for userDisplayName with a wrong value.

  function userDisplayName({displayName: dname}) {
     return dname;
  }
  

• f is not tagged with function kind.

   let [f] = [function() {}];
  

  I will not try to fix this. I cannot find any easy way to remove this limitation.

ref. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment

[codecov]

Codecov Report

Attention: Patch coverage is 95.71429% with 6 lines in your changes missing coverage. Please review.

Project coverage is 85.94%. Comparing base (f9dc9c8) to head (b719aec).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
parsers/jscript.c	95.71%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3435      +/-   ##
==========================================
+ Coverage   85.91%   85.94%   +0.02%     
==========================================
  Files         239      239              
  Lines       58851    58963     +112     
==========================================
+ Hits        50563    50673     +110     
- Misses       8288     8290       +2     

☔ View full report in Codecov by Sentry.
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[masatake]

Rebased on the latest master branch.
@jafl, this pull request still has some TODO items. But I would like to get your review.

[jafl]

@masatake Thanks for rebasing! I have had this one on my todo list for a while. I will try to get to it soon.

[whoshallsucceed]

It seems to be working to a limit.

Deconstruction in a multilines block of code fails:

files.push({
  relative, // <----
  basename: name,
  absolute: loc,
  mtime: +stat.mtime
});

I don't know if it is related but the following form fails as well:

computed: {
  ...mapGetters([
    'getAsylumAssistant',
    'getModel',
    'getType',
  ]),
},

I thought these forms would work but apparently not:

this.stagedlocalRecord = { localRecord, localRecordIndex }
// ---
return this.saveData({ partyId, id, data, rubyType: dbTypes[type], jsType: type })
// ---
createDocketEntryModel ({ commit, state }, requestData) {
  // ...
}

And there might be more but it takes too long for me to check all the warnings 😅

[masatake]

@AdrienGiboire thank you.

files.push({
  relative, // <----

I don't understand this. Is relative a variable?
Is there any document that describes this syntax?

I cannot find the notation in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment.

[jafl]

files.push({
  relative, // <----

This assumes that relative is a variable, and it is shorthand for

files.push({
  relative: relative,

[masatake]

@jafl Thank you. So the question is, in which context can we use the shorthand syntax?

[whoshallsucceed]

Here it describes the case you're wondering about, especially this part:

Function parameter definitions

As developers, we can often expose more ergonomic APIs by accepting a single object with multiple properties as a parameter instead of forcing our API consumers to remember the order of many individual parameters. We can use destructuring to avoid repeating this single parameter object whenever we want to reference one of its properties:

function removeBreakpoint({ url, line, column }) {
  // ...
}

Knowing that it should support default values.

jQuery.ajax = function (url, {
  async = true,
  beforeSend = noop,
  cache = true,
  complete = noop,
  crossDomain = false,
  global = true,
  // ... more config
}) {
  // ... do stuff
};

Basically, if a variable is between {} and there is no explicit key, it's meant to be desconstructed.
If an assignment is between {}, it's meant to be desconstructed and have a default value.

[masatake]

@AdrienGiboire Thank you.

function removeBreakpoint({ url, line, column }) {
  // ...
}

I found even this input causes the warning message.
I found we can skip such parameter lists because the JavaScript parser doesn't extract parameters as tags. I added a commit for this change.

files.push({
  relative, // <----
  basename: name,
  absolute: loc,
  mtime: +stat.mtime
});

It seems that we must improve skipArgumentList(). I will inspect this one more.

[masatake]

$ cat /tmp/foo.js                                                                                                                                     
cat /tmp/foo.js                                                                                                                                       
computed: {                                                                                                                                           
  ...mapGetters([                                                                                                                                     
    'getAsylumAssistant',                                                                                                                             
    'getModel',                                                                                                                                       
    'getType',                                                                                                                                        
  ]),                                                                                                                                                 
},                                                                                                                                                    
$ node foo.js                                                                                                                                         
node foo.js                                                                                                                                           
node:internal/modules/cjs/loader:998                                                                                                                  
  throw err;                                                                                                                                          
  ^                                                                                                                                                   
                                                                                                                                                      
Error: Cannot find module '/home/jet/var/ctags-github/foo.js'                                                                                         
    at Module._resolveFilename (node:internal/modules/cjs/loader:995:15)                                                                              
    at Module._load (node:internal/modules/cjs/loader:841:27)                                                                                         
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)                                                             
    at node:internal/main/run_main_module:23:47 {                                                                                                     
  code: 'MODULE_NOT_FOUND',                                                                                                                           
  requireStack: []                                                                                                                                    
}                                                                                                                                                     
                                                                                                                                                      
Node.js v18.12.1                          

Could you provide an example input that node accepts?
Thank you.

[whoshallsucceed]

$ cat /tmp/foo.js                                                                                                                                     
cat /tmp/foo.js                                                                                                                                       
computed: {                                                                                                                                           
  ...mapGetters([                                                                                                                                     
    'getAsylumAssistant',                                                                                                                             
    'getModel',                                                                                                                                       
    'getType',                                                                                                                                        
  ]),                                                                                                                                                 
},                                                                                                                                                    
$ node foo.js                                                                                                                                         
node foo.js                                                                                                                                           
node:internal/modules/cjs/loader:998                                                                                                                  
  throw err;                                                                                                                                          
  ^                                                                                                                                                   
                                                                                                                                                      
Error: Cannot find module '/home/jet/var/ctags-github/foo.js'                                                                                         
    at Module._resolveFilename (node:internal/modules/cjs/loader:995:15)                                                                              
    at Module._load (node:internal/modules/cjs/loader:841:27)                                                                                         
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)                                                             
    at node:internal/main/run_main_module:23:47 {                                                                                                     
  code: 'MODULE_NOT_FOUND',                                                                                                                           
  requireStack: []                                                                                                                                    
}                                                                                                                                                     
                                                                                                                                                      
Node.js v18.12.1                          

Could you provide an example input that node accepts? Thank you.

Did you mean to run node /tmp/foo.js instead?

[masatake]

Did you mean to run node /tmp/foo.js instead?

You are correct. However, even though I specified /tmp/foo.js, I got an error.

$ cat /tmp/foo.js 
computed: {                                                                                                                                           
  ...mapGetters([                                                                                                                                     
    'getAsylumAssistant',                                                                                                                             
    'getModel',                                                                                                                                       
    'getType',                                                                                                                                        
  ]),                                                                                                                                                 
},
$ node /tmp/foo.js 
/tmp/foo.js:2
  ...mapGetters([                                                                                                                                     
  ^^^

SyntaxError: Unexpected token '...'
    at internalCompileFunction (node:internal/vm:73:18)
    at wrapSafe (node:internal/modules/cjs/loader:1178:20)
    at Module._compile (node:internal/modules/cjs/loader:1220:27)
    at Module._extensions..js (node:internal/modules/cjs/loader:1310:10)
    at Module.load (node:internal/modules/cjs/loader:1119:32)
    at Module._load (node:internal/modules/cjs/loader:960:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:86:12)
    at node:internal/main/run_main_module:23:47

Node.js v18.18.2

[whoshallsucceed]

You can try something like this:

const embedded = { foo: 'bar' }
const something = {
  ...embedded,
  baz: 'fox',
}

[masatake]

Thank you. Based on your hit, I modified /tmp/foo.js:

$ cat /tmp/foo.js
const mapGetters = function() {}
const computed = {                                                                                                                                           
  ...mapGetters([                                                                                                                                     
    'getAsylumAssistant',                                                                                                                             
    'getModel',                                                                                                                                       
    'getType',                                                                                                                                        
  ]),                                                                                                                                                 
}
$ node /tmp/foo.js
$

Works fine. Thank you.

[yamato@dev64]~/var/ctags-github% git rebase master
Successfully rebased and updated refs/heads/js--destructural-binding.

[yamato@dev64]~/var/ctags-github% make
...
[yamato@dev64]~/var/ctags-github% ./ctags -o - /tmp/foo.js 
ctags: Notice: ignoring null tag in /tmp/foo.js(line: 3, language: JavaScript)
computed	/tmp/foo.js	/^const computed = {                                                                              /;"	C
mapGetters	/tmp/foo.js	/^const mapGetters = function() {}$/;"	f

I cannot remember what we were talking about quickly. But I guess the issue is about ignoring null tag warning.

[masatake]

[yamato@dev64]~/var/ctags-github% cat /tmp/bar.js         
const embedded = { foo: 'bar' }
const something = {
  ...embedded,
  baz: 'fox',
}
[yamato@dev64]~/var/ctags-github% ./ctags -o - /tmp/bar.js
ctags: Notice: ignoring null tag in /tmp/bar.js(line: 3, language: JavaScript)
embedded	/tmp/bar.js	/^const embedded = { foo: 'bar' }$/;"	v
foo	/tmp/bar.js	/^const embedded = { foo: 'bar' }$/;"	p	variable:embedded
something	/tmp/bar.js	/^const something = {$/;"	C

I found two issues here:

• the null tag warning
• Though foo in embedded is extracted, baz in something is not.

embedded in something is not a definition, so we don't have to extract it as a definition tag. Instead, THe parser should skip the ...embedded.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

[whoshallsucceed]

It makes sense but at the same time would it not be legit to have the definition?

For example, you can have something like:

const something = {
  fn: () => { /* doing something */ },
}

It would make sense to have the definition of the function referenced. What do you think?

[masatake]

This is a difficult question. However, regarding the example, fn should be tagged as a definition tag. fn is introduced as a new name.

const embedded = { foo: 'bar' }
const something = {
  ...embedded,
  baz: 'fox',
}

In my understanding, this is the same as:

const something = {
  foo: 'bar',
  baz: 'fox',
}

Am I correct?

The embedded in something is not a key.
So embedded should not be tagged as a definition tag.
It is a reference tag having shredded role of variable (or unknown) kind.

---

Added after commenting

[yamato@dev64]~/var/ctags-github% cat /tmp/bar.js 
const embedded = { foo: 'bar' }
const something = {
  ...embedded,
  baz: 'fox',
}

something.foo;

[yamato@dev64]~/var/ctags-github% node /tmp/bar.js

My understanding may be correct.

[masatake]

[yamato@dev64]~/var/ctags-github% git diff                
diff --git a/parsers/jscript.c b/parsers/jscript.c
index 78f563dde..f316d7f7d 100644
--- a/parsers/jscript.c
+++ b/parsers/jscript.c
@@ -2019,6 +2019,12 @@ static bool parseMethods (tokenInfo *const token, int class_index,
 
            deleteToken (saved_token);
        }
+       else if (isType (token, TOKEN_DOTS))
+       {
+           /* maybe spread operator. Just skip the next expression. */
+           findCmdTerm(token, true, true);
+           continue;
+       }
 
        if (! isType (token, TOKEN_KEYWORD) &&
            ! isType (token, TOKEN_SEMICOLON))
[yamato@dev64]~/var/ctags-github% cat /tmp/bar.js 
const embedded = { foo: 'bar' }
const something = {
  ...embedded,
  baz: 'fox',
}
[yamato@dev64]~/var/ctags-github% ./ctags --sort=no -o - /tmp/bar.js
foo	/tmp/bar.js	/^const embedded = { foo: 'bar' }$/;"	p	variable:embedded
embedded	/tmp/bar.js	/^const embedded = { foo: 'bar' }$/;"	v
baz	/tmp/bar.js	/^  baz: 'fox',$/;"	p	variable:something
something	/tmp/bar.js	/^const something = {$/;"	v

[masatake]

Surprisingly, the change for skipping spread operators works well with the current master branch. So I can submit it as a standalone pull request.

[masatake]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

This tells spread syntax.
I'm looking for the spread operator, ",@" in lisp..

[whoshallsucceed]

const embedded = { foo: 'bar' }
const something = {
  ...embedded,
  baz: 'fox',
}

In my understanding, this is the same as:

const something = {
  foo: 'bar',
  baz: 'fox',
}

Am I correct?

Pretty much, yes.

Surprisingly, the change for skipping spread operators works well with the current master branch. So I can submit it as a standalone pull request.

It does look good 👍

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

This tells spread syntax. I'm looking for the spread operator, ",@" in lisp..

I'm not sure I understand what you mean. And I know nothing about Lisp so I can't relate ^^' I tried googling but I have not seen ,@ 🤷‍♂️

[masatake]

@AdrienGiboire Sorry, after rereading the page at developer.mozilla.org, "spread syntax" is the correct word.

[masatake]

@jafl, can I merge this?

[masatake]

.b test cases must be added.

[masatake]

@jafl, can I merge this?