x/tools/go/ssa: generic methods with empty bodies panic with SanityCheckFunctions

[eliasnaur]

Go version

go version go1.24.2 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/a/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/a/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/9c/t7b8z6m93sxgr4m4m4kbvllw0000gn/T/go-build2808707577=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/a/proj/golang-tools/go.mod'
GOMODCACHE='/Users/a/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/a/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/a/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

In x/tools, add a test,

% jj diff
diff --git a/go/ssa/builder_test.go b/go/ssa/builder_test.go
index a48723bd2..2a40a200d 100644
--- a/go/ssa/builder_test.go
+++ b/go/ssa/builder_test.go
@@ -1045,6 +1045,7 @@ func TestFixedBugs(t *testing.T) {
        for _, name := range []string{
                "issue66783a",
                "issue66783b",
+               "issueXXXXX",
        } {

                t.Run(name, func(t *testing.T) {
diff --git a/go/ssa/testdata/fixedbugs/issueXXXXX.go b/go/ssa/testdata/fixedbugs/issueXXXXX.go
new file mode 100644
index 000000000..5a7c4ef56
--- /dev/null
+++ b/go/ssa/testdata/fixedbugs/issueXXXXX.go
@@ -0,0 +1,10 @@
+package issueXXXXX
+
+type genericType[T any] struct{}
+
+func (genericType[T]) methodWithoutBody()
+
+func callMethodWithoutBody() {
+       msg := &genericType[int]{}
+       msg.methodWithoutBody()
+}

What did you see happen?

$ go test ./go/ssa
# Name: testdata/a.init
# Package: testdata/a
# Synthetic: package initializer
func init():
0:                                                                entry P:0 S:2
        t0 = *init$guard                                                   bool
        if t0 goto 2 else 1
1:                                                           init.start P:1 S:1
        *init$guard = true:bool
        t1 = testdata/b.init()                                               ()
        jump 2
2:                                                            init.done P:2 S:0
        return

# Name: testdata/a.A
# Package: testdata/a
# Location: /var/folders/9c/t7b8z6m93sxgr4m4m4kbvllw0000gn/T/TestNoIndirectCreatePackage2015203071/001/a/a.go:5:6
func A():
0:                                                                entry P:0 S:0
        t0 = testdata/b.B{}:testdata/b.B.C [#0]                    testdata/c.C
        t1 = (testdata/c.C).F(t0)                                            ()
        return

# Name: (testdata/c.C).F
# Synthetic: from type information (on demand)
# Location: /var/folders/9c/t7b8z6m93sxgr4m4m4kbvllw0000gn/T/TestNoIndirectCreatePackage2015203071/001/c/c.go:4:10
func (testdata/c.C) F():
        (external)

Error: function (issueXXXXX.genericType[int]).methodWithoutBody[int]: function transient field 'subst' is not nil
# Name: (issueXXXXX.genericType[int]).methodWithoutBody[int]
# Synthetic: instance of methodWithoutBody
# Location: /Users/a/proj/golang-tools/go/ssa/testdata/fixedbugs/issueXXXXX.go:5:23
func (genericType[int]) methodWithoutBody[int]():
        (external)

--- FAIL: TestFixedBugs (0.00s)
    --- FAIL: TestFixedBugs/issueXXXXX (0.00s)
panic: SanityCheck failed [recovered]
        panic: SanityCheck failed

goroutine 1257 [running]:
testing.tRunner.func1.2({0x10134bd60, 0x1013c8d20})
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/testing/testing.go:1734 +0x1ac
testing.tRunner.func1()
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/testing/testing.go:1737 +0x334
panic({0x10134bd60?, 0x1013c8d20?})
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/runtime/panic.go:792 +0x124
golang.org/x/tools/go/ssa.mustSanityCheck(0x14003064600, {0x0?, 0x0?})
        /Users/a/proj/golang-tools/go/ssa/sanity.go:48 +0x94
golang.org/x/tools/go/ssa.(*Function).done.func1(0x14003064600)
        /Users/a/proj/golang-tools/go/ssa/func.go:415 +0x19c
golang.org/x/tools/go/ssa.(*Function).done(0x14001ef4fc0?)
        /Users/a/proj/golang-tools/go/ssa/func.go:418 +0x4c
golang.org/x/tools/go/ssa.(*builder).buildFunction(0x1?, 0x14003064600)
        /Users/a/proj/golang-tools/go/ssa/builder.go:2907 +0x114
golang.org/x/tools/go/ssa.(*builder).iterate(0x14001ef4fc0)
        /Users/a/proj/golang-tools/go/ssa/builder.go:2891 +0x2c
golang.org/x/tools/go/ssa.(*Package).build(0x14001272380)
        /Users/a/proj/golang-tools/go/ssa/builder.go:3174 +0xc8
sync.(*Once).doSlow(0x14004db4c60?, 0x14003046c00?)
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/sync/once.go:78 +0xf0
sync.(*Once).Do(...)
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/sync/once.go:69
golang.org/x/tools/go/ssa.(*Package).Build(...)
        /Users/a/proj/golang-tools/go/ssa/builder.go:3163
golang.org/x/tools/go/ssa/ssautil.BuildPackage(0x14003042310, 0x14002781a80, 0x14003046c00, {0x14003484958, 0x1, 0x1}, 0x108)
        /Users/a/proj/golang-tools/go/ssa/ssautil/load.go:187 +0x340
golang.org/x/tools/go/ssa_test.TestFixedBugs.func1(0x14002b35a40)
        /Users/a/proj/golang-tools/go/ssa/builder_test.go:1063 +0x188
testing.tRunner(0x14002b35a40, 0x1400304a0c0)
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/testing/testing.go:1792 +0xe4
created by testing.(*T).Run in goroutine 1254
        /nix/store/fd2s1z3why92qn8w7j6r0xlarikpv27v-go-1.24.2/share/go/src/testing/testing.go:1851 +0x374
FAIL    golang.org/x/tools/go/ssa       1.354s
FAIL

What did you expect to see?

No error.

[adonovan]

Thanks for the bug report and test case. Fix pending.

[gopherbot]

Change https://go.dev/cl/669955 mentions this issue: go/ssa: clear Function.subst after building bodyless function