Generic function unnexpectedly returns 'QVoid' when called from another file

[rhpreston]

Describe the bug

While writing unit tests for a generic-typed function, I ran into some strange behavior. The function works perfectly when called from the same file, but it seems to return a QVoid when called from the test suite, instead of the expected Bool.

To Reproduce

• Using Visual Studio, create a new Q# Test Project with boilerplate TestSuiteRunner.cs
• Create a new Q# file in the same namespace containing a generic-typed function that returns a Bool
• Write a test that calls the function and uses the result in some way.
• Try to build the project.

Example

Target.qs:

namespace Quantum.QSharpTestProject1
{
    open Microsoft.Quantum.Intrinsic;
    open Microsoft.Quantum.Canon;

    function BuggyReturn<'T> (param: 'T): Bool
    {
        return true;
    }

    function AssertBuggyReturn<'T> (param: 'T): Unit
    {
        if (not BuggyReturn<'T>(param))
        {
            fail "BuggyReturn returned false";
        }
    }
}

Tests.qs:

namespace Quantum.QSharpTestProject1
{
    open Microsoft.Quantum.Intrinsic;
    open Microsoft.Quantum.Canon;
    open Microsoft.Quantum.Diagnostics;


    function BuggyReturnTest () : Unit
    {
        AssertBuggyReturn<Int>(0); // This works fine!
        if (not BuggyReturn<Int>(0)) // This gives error
        {
            fail "BuggyReturn returned false";
        }
    }
}

Note that in the above example, AssertBuggyReturn builds just fine, but BuggyReturnTest does not. It gives the error, Operator '!' cannot be applied to operand of type 'QVoid'.

Expected behavior

The code in AssertBuggyReturn and BuggyReturnTest is exactly the same, and therefore should behave identically. BuggyReturn should always return a Bool and not QVoid.

System information

QDK extension version: 0.9.1909.3002

Visual Studio information:

Microsoft Visual Studio Enterprise 2019
Version 16.3.5
VisualStudio.16.Release/16.3.5+29411.108
Microsoft .NET Framework
Version 4.7.03190

Installed Version: Enterprise

Visual C++ 2019   00433-90101-61314-AA195
Microsoft Visual C++ 2019
...

[bettinaheim]

@rhpreston Thanks for reporting!
I should get around to taking a look at this some time this week.

[bettinaheim]

Fixed with PR #88.

[rhpreston]

For anyone who happens upon this thread before the PR goes through, I realized you can avoid the error by not explicitly specifying the type in the function call. For example, BuggyReturn(0).

[bettinaheim]

Done.