commit 85a12eac55c6a6cdd054145540b888bede3addb2
author Nicholas Shahan <nshahan@google.com> Mon Sep 20 23:29:45 2021 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Mon Sep 20 23:29:45 2021 +0000
tree ff67f6bcf567da36311ccae0927e0d6fdc2702be
parent e8cd9f0c44dfc14c75b3c3832f4d191afd036143

[ddc] Fix missing type variable bounds subtype check

When testing the subtype relation between two generic function types,
uninstantiated type variables can appear as an argument or return type
of one function while a concrete type appears in corresponding
position of the other function. A subtype relation can be established
if the bound of the type variable is a subtype of the concrete type.
For example given a type variable T with bound B and a concrete type
C we can say:

T <: C when T <: B <: C holds.

T <: B is true by the definition of interface subtypes `T extends B`.
This change adds a test for B <: C.

Add a new class used only when it appears we may need to test these
subtype relations. The class is used to plumb the bound information
of type variables further into the subtype check algorithm where it
is now tested.

Add a top level variable to index the total number of type arguments
seen during a subtype check through nested function types.

Change-Id: If6aa13e7b758f7fedcb5dbd8e09d366082198e61
Fixes: https://github.com/dart-lang/sdk/issues/38816
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/213527
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Mayank Patke <fishythefish@google.com>