[go] go/types, types2: handle unconstrained type parameters correctly in a few places

[Gopher Robot (Gerrit)]

Gopher Robot submitted the change

Change information

Commit message:

go/types, types2: handle unconstrained type parameters correctly in a few places

When iterating over a type set via a range clause, am unconstrained
type set produces a single (nil, nil) result. This was not properly
accounted for in a few places:

- In the code for the append and copy built-in, handle the (nil, nil)
  case.
- Likewise, in NewSignatureType, panic with the correct (string) error
  in this case.

Check all remaining places where we iterate over type sets with range
for correctness.

Fixes #78163.

Change-Id: If0f33f43dad59b4b5ef4c310f80522c25c6e251f

Reviewed-on: https://go-review.googlesource.com/c/go/+/755941

Reviewed-by: Robert Griesemer <g...@google.com>

LUCI-TryBot-Result: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>

Reviewed-by: Mark Freeman <markf...@google.com>

Auto-Submit: Robert Griesemer <g...@google.com>

Files:

• M src/cmd/compile/internal/types2/builtins.go
• M src/cmd/compile/internal/types2/issues_test.go
• M src/cmd/compile/internal/types2/signature.go
• M src/cmd/compile/internal/types2/under.go
• M src/go/types/builtins.go
• M src/go/types/issues_test.go
• M src/go/types/signature.go
• M src/go/types/under.go
• A src/internal/types/testdata/fixedbugs/issue78163.go

Change size: S

Delta: 9 files changed, 37 insertions(+), 12 deletions(-)

Branch: refs/heads/master

Submit Requirements:

• Code-Review: +2 by Mark Freeman, +1 by Robert Griesemer
• TryBots-Pass: LUCI-TryBot-Result+1 by Go LUCI

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Gerrit

Gerrit-MessageType: merged

Gerrit-Project: go

Gerrit-Branch: master

Gerrit-Change-Id: If0f33f43dad59b4b5ef4c310f80522c25c6e251f

Gerrit-Change-Number: 755941

Gerrit-PatchSet: 4

Gerrit-Owner: Robert Griesemer <g...@google.com>

Gerrit-Reviewer: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>

Gerrit-Reviewer: Gopher Robot <go...@golang.org>

Gerrit-Reviewer: Mark Freeman <markf...@google.com>

Gerrit-Reviewer: Robert Griesemer <g...@google.com>