Editorial: Fix omitted return types of functions that can return empty

[kimjg1119]

Certain functions may return ~empty~, though this is not always reflected in the return type. Each identified error is presented alongside specific code examples, where scenarios include the presence of ~empty~ values.

All of these errors were discovered using ESMeta, so executing the provided code in ESMeta may help obtain a detailed execution path(Also note that some of the codes only compile in the dev branch).

Fixed functions

LabelledEvaluation

LabelledEvaluation of LabelledItem with argument newLabelSet can return ~empty~ because of the break statement, the return value can be ~empty~.

Scenario:

label: break label;
label: function f() {}
label: {}
label: var x;
label: ;

Details (ESMeta)

[ReturnTypeMismatch] Block[12989] return statement in LabelledStatement[0,0].LabelledEvaluation (step 5, 7:12-34)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[ESValue | Enum[~empty~]] | Abrupt[break, continue, throw]

[ReturnTypeMismatch] Block[12991] return statement in LabelledItem[1,0].LabelledEvaluation (step 1, 2:12-57)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[Enum[~empty~]]

[ReturnTypeMismatch] Block[12993] return statement in Statement[0,0].LabelledEvaluation (step 1, 2:12-47)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[ESValue | Enum[~empty~]] | Abrupt[break, continue, throw]

[ReturnTypeMismatch] Block[12995] return statement in Statement[1,0].LabelledEvaluation (step 1, 2:12-47)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[Enum[~empty~]] | Throw

[ReturnTypeMismatch] Block[12997] return statement in Statement[2,0].LabelledEvaluation (step 1, 2:12-47)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[Enum[~empty~]]

CatchClauseEvaluation

The Completion(Evaluation of Block) could result in ~empty~. Since it flows into B and returns immediately, the return type should account for ~empty~.

Scenario:

try { x; } catch (e) {}
try { x; } catch {}

Note that each line corresponds to the bug in the details.

Details (ESMeta)

[ReturnTypeMismatch] Block[13050] return statement in Catch[0,0].CatchClauseEvaluation (step 9, 13:12-25)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[ESValue | Enum[~empty~]] | Abrupt[break, continue, throw]

[ReturnTypeMismatch] Block[13052] return statement in Catch[1,0].CatchClauseEvaluation (step 1, 2:12-43)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[ESValue | Enum[~empty~]] | Abrupt[break, continue, throw]

EvaluateFunctionBody

Since the evaluation of a single block is an ~empty~, an evaluation of the FunctionStatementList can be ~empty~ too.

Scenario:

function f() { {} } f();

Details (ESMeta)

[ReturnTypeMismatch] Block[13224] return statement in FunctionBody[0,0].EvaluateFunctionBody (step 2, 3:12-59)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[ESValue | Enum[~empty~]] | Abrupt[break, continue, throw]

EvaluateClassStaticBlockBody

Similar to EvaluateFunctionBody, this function can return ~empty~.

Scenario:

class A { static { {} } }

Details (ESMeta)

[ReturnTypeMismatch] Block[14021] return statement in ClassStaticBlockBody[0,0].EvaluateClassStaticBlockBody (step 3, 4:12-67)
- expected: Normal[ESValue] | Abrupt
- actual  : Normal[ESValue | Enum[~empty~]] | Abrupt[break, continue, throw]

[nicolo-ribaudo]

Note about the title: this is Editorial, because the change is not observable from JS code.

[bakkot]

This is a duplicate of #2924. Apologies for leaving that open for so long; I'm hoping we can merge it soon.