0000448: singleton warning generation ignores variables in quantifications

Mercury Bugs - mercury
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ID	Project	Category	View Status	Date Submitted	Last Update
0000448	mercury	Bug	public	2018-02-07 05:30	2018-02-07 05:30

Reporter	zs
Assigned To	zs
Priority	normal	Severity	minor	Reproducibility	always
Status	assigned	Resolution	open
Platform		OS		OS Version
Product Version
Target Version		Fixed in Version

Summary	0000448: singleton warning generation ignores variables in quantifications
Description	The problem is that quantification replaces the list of variables being quantified by a scope, ostensibly because that information is not needed by later compiler passes. However, it is needed by the code that generates warnings for singleton predicates. As it is, we get bad singleton warnings for code such as some [X] ( ... X ... ) and may NOT get singleton warnings for code such as some [X] ( ... code in which there is no variable named X ... )
Steps To Reproduce	The two halves of the problem are demonstrated by the test cases valid/bad_singleton_warning.m and warnings/missing_singleton_warning.m, which I just added to the repository.
Additional Information	Simply keeping the quantified variables in place causes problems for later passes; it is such code in these later passes that are the actual bugs.
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