go/types: types.CheckExpr returns error when 'FuncType' ast.Expr has TypeParams

[csgura]

Go version

go1.22

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/gura/Library/Caches/go-build'
GOENV='/Users/gura/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/gura/go/pkg/mod'
GONOPROXY='*.uangel.com'
GONOSUMDB='*.uangel.com'
GOOS='darwin'
GOPATH='/Users/gura/go'
GOPRIVATE='*.uangel.com'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.22.0/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.22.0/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/gura/git/fp/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/mr/dvhjg7zd4l125pln73bqyr400000gp/T/go-build857521387=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

https://go.dev/play/p/ZPv6Er1H6K3

What did you see happen?

error 'undefined: A' is returned

What did you expect to see?

In Go version 1.21, there were no errors

[prattmic]

cc @griesemer @findleyr

[griesemer]

Hm, this does indeed look like a regression.
More compact reproducer (may be used a test case in fix): https://go.dev/play/p/XZWMNTkAOHo

[griesemer]

This is actually working as intended; the fact that the code worked for 1.21 was a bug in 1.21 which was fixed by CL 544035.

Evaluating the function type expression in your code (line 16) requires that the type parameters (here A) are in scope. They are not in scope at the start of the function type, but certainly after the function type. You can make your example work by changing the position provided in line 16 to the end position (example). With that change, the example works and prints OK.

So not a release blocker and not a bug. Will close with a test case for future reference.

[gopherbot]

Change https://go.dev/cl/567215 mentions this issue: go/types: added test case for Checker.CheckExpr