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JS: classify generated data files #108

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semmle-qlci merged 1 commit into from Aug 29, 2018
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JS: classify generated data files #108

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18 changes: 17 additions & 1 deletion javascript/ql/src/semmle/javascript/GeneratedCode.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,21 @@ private predicate hasManyInvocations(TopLevel tl) {
)
}

/**
* Holds if `f` is side effect free, and full of primitive literals, which is often a sign of generated data code.
*/
private predicate isData(File f) {
// heuristic: `f` has more than 1000 primitive literal expressions ...
count(SyntacticConstants::PrimitiveLiteralConstant e | e.getFile() = f) > 1000 and
// ... but no expressions with side effects ...
not exists (Expr e |
e.getFile() = f and
e.isImpure() and
// ... except for variable initializers
not e instanceof VariableDeclarator
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@xiemaisi xiemaisi Aug 27, 2018

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Does this mean we consider VariableDeclarators to be impure? That seems undesirable.

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@ghost ghost Aug 27, 2018

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Yes, but that seems right to me.
They do modify the scope object after all.

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@xiemaisi xiemaisi Aug 27, 2018

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That's true, but modelling it seems overkill, particularly since we don't even model the scope object. Also, that modification isn't observable in any way, is it?

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@ghost ghost Aug 27, 2018

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Hmm. I could go either way on this. On the one hand, shadowing variables in enclosing scopes and creation of properties on the global object are easily observable side effects, but on the other hand, I see what you mean regarding the expressive power of our analysis.
Do you want a change in this PR?

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@xiemaisi xiemaisi Aug 28, 2018

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You are right, of course, there are observable side effects, but I would still hesitate to ascribe them to the declarator, so on the whole I'd be in favour of changing this. It seems like a fairly minor and harmless change that would make this predicate look a bit less confusing.

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@ghost ghost Aug 28, 2018

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Done.
Do we skip the full dist-compare for this change?

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@xiemaisi xiemaisi Aug 28, 2018

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Thanks. Yes, we do.

)
}

/**
* Holds if `tl` looks like it contains generated code.
*/
Expand All @@ -108,7 +123,8 @@ predicate isGenerated(TopLevel tl) {
tl instanceof GWTGeneratedTopLevel or
tl instanceof DartGeneratedTopLevel or
exists (GeneratedCodeMarkerComment gcmc | tl = gcmc.getTopLevel()) or
hasManyInvocations(tl)
hasManyInvocations(tl) or
isData(tl.getFile())
}

/**
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2 changes: 2 additions & 0 deletions javascript/ql/test/query-tests/filters/ClassifyFiles/ClassifyFiles.expected
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@@ -1,5 +1,7 @@
| ai.1.2.3-build0123.js:0:0:0:0 | ai.1.2.3-build0123.js | library |
| bundle-directive.js:0:0:0:0 | bundle-directive.js | generated |
| data.js:0:0:0:0 | data.js | generated |
| exported-data.js:0:0:0:0 | exported-data.js | generated |
| jison-lex.js:0:0:0:0 | jison-lex.js | generated |
| jison.js:0:0:0:0 | jison.js | generated |
| jquery-datatables.js:0:0:0:0 | jquery-datatables.js | library |
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