The IRS says, "An employee covered by an HDHP and a health FSA or an HRA that pays or reimburses qualified medical expenses generally can’t make contributions to an HSA." (page 5 of Publication 969)

The exceptions are if the HRA is a limited-purpose HRA, only for

• Liabilities incurred under workers' compensation laws, tort liabilities, or liabilities related to ownership or use of property.
• A specific disease or illness.
• A fixed amount per day (or other period) of hospitalization.
• Accidents.
• Disability.
• Dental care.
• Vision care.
• Long-term care.

There are several other exceptions, which are listed on page 5 of Pub 969 (https://www.irs.gov/pub/irs-pdf/p969.pdf), but a general purpose HRA (able to reimburse you for any medical expense) disqualifies you from making HSA contributions.

[Edited 3/23/2020 11:58 am CDT - updated page references]