the "special-case inliners for known pure functions that compute types" are broken

[wongwill86]

This can be reproduced with different versions of julia (.4 to .5) as well as using BaseTestDeprecated vs Base.Test.

Example below:

This is the module we are testing:

julia> module ToTest
       function get_type(s::String)
           println("get_type being called")
           if s != "UInt16"
               error("I don't know what $s is.")
           end
           return UInt16
       end
       function get_string(s::String)
           println("get_string being called")
           if s != "UInt16"
               error("I'm erroring for fun")
           end
           return s
       end
       end

This is the module that tests ToTest with old Base.Test aka BaseTestDeprecated

julia> module TesterBaseDeprecated
       import ToTest
       using BaseTestDeprecated
       const Test = BaseTestDeprecated
       function test_get_type(s::String)
           @test_throws Exception ToTest.get_type(s)
       end
       function test_get_string(s::String)
           @test_throws Exception ToTest.get_string(s)
       end
       end

This is the module that tests ToTest with new Base.Test

julia> module TesterBaseNext
       import ToTest
       using Base.Test
       function test_get_type(s::String)
           @test_throws Exception ToTest.get_type(s)
       end
       function test_get_string(s::String)
           @test_throws Exception ToTest.get_string(s)
       end
       end

In this example, ToTest.get_type(s::String) should throw an error if the s is not "UInt16"
BaseTestDeprecated works correctly by catching the error:

julia> TesterBaseDeprecated.test_get_type("should throw")
get_type being called
ErrorException("I don't know what should throw is.")

New Base.Test works incorrectly by not even running the function

julia> TesterBaseNext.test_get_type("should throw")
Test Failed
  Expression: ToTest.get_type(s)
    Expected: Exception
  No exception thrown
ERROR: There was an error during testing
 in record(::Base.Test.FallbackTestSet, ::Base.Test.Fail) at ./test.jl:397
 in do_test_throws(::Base.Test.Returned, ::Expr, ::Type{T}) at ./test.jl:329
 in test_get_type(::String) at ./REPL[18]:5

ToTest.test_get_string works correctly:

julia> TesterBaseNext.test_get_string("should throw")
get_string being called
Test Passed
  Expression: ToTest.get_string(s)
      Thrown: ErrorException

julia> TesterBaseDeprecated.test_get_string("should throw")
get_string being called
ErrorException("I'm erroring for fun")

Is there something wrong the way we are using @test_throws with the new Base.Test?

[TotalVerb]

Smaller repro:

julia> @noinline f(n) = n ? error() : Int
f (generic function with 1 method)

julia> g() = Union{f(true)}
g (generic function with 1 method)

julia> g()
Int64

Some constructors like Nullable also do this.

[vtjnash]

This is the inlining bug noted at b3dbc05#commitcomment-17890328 (where f in the example here is apply_type)