"Unassigned local variable" is reported for a variable, which is always assigned

[DoctorKrolic]

Version Used:
VS 17.14.13

Steps to Reproduce:

int val;

try
{
	val = 1;
}
catch
{
	val = 2;
}
finally
{
    Console.WriteLine(val); // Use of unassigned local variable 'val'
}

Diagnostic Id:
CS0165

Expected Behavior:
No error since val is assigned in both try and catch "branches", so it is 100% assigned at the point of finally

Actual Behavior:
Compiler error CS0165: Use of unassigned local variable 'val'

[CyrusNajmabadi]

I'm not sure if this is incorrect. The compiler doesn't know if an errant thread .abort will happen prior to either/both val assignments.

The finally truly could run without the assignment happening.

basically, the end of the try/catch assignments are not guaranteed to be reachable, and as such the val may not be assigned. But the finally will still run as execution exits due to that abort.

[CyrusNajmabadi]

@jaredpar for assessment.

[RikkiGibson]

The assignments in 'try' and 'catch' do not necessarily flow to the 'finally' block. I believe there is an assumption that the point at the start of the 'try' or the 'catch' can branch directly to the 'finally'. You could imagine a Thread.Abort() call causing this to occur.

https://github.com/dotnet/csharpstandard/blob/draft-v8/standard/variables.md#94415-try-finally-statements

For a statement stmt of the form:

try «try_block» finally «finally_block»

...

• The definite-assignment state of v at the beginning of finally_block is the same as the definite-assignment state of v at the beginning of stmt.

And the following section states that try-catch-finally is analyzed as if it were try { try-catch; } finally { }.

[RikkiGibson]

Closing as by design.