Add assertions when implicitly returning from a function

[phpnode]

Currently if a function implicitly returns undefined (by leaving the function without an explicit return statement) we won't generate a check for it, e.g:

function foo (): string {
  // no return
}

currently compiles to:

function foo () {
  const _returnType = t.return(t.string()); 
  // no return
}

We should insert a call to _returnType.assert(undefined) at these points.

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IssueHunt Summary

Backers (Total: $20.00)

• issuehunt ($20.00)

Submitted pull Requests

• #249 For #2: Add explicit return (with assetion) if last function statement is not return one
• #301 fix: enforce implicit return assertion for non-empty function bodies
• #306 Fix implicit return assertions after fallthrough statements

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[phpnode]

marking as low priority because Flow already catches this.

[issuehunt-oss]

@issuehunt has funded $20.00 to this issue.

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[szw9999]

Submitted PR #302 for this issue: #302. It fixes the missing implicit-return assertion when an annotated function has statements but still falls through without an explicit return.