proc: add regression test for issue #3548 (#3553)

Issue #3548 describes a bug in the compiler which was fixed by commit
505e50b. But this case wasn't covered by our current tests (obviously)
and the fix in the compiler looks accidental so it's worth adding a
test for it.

Fixes #3548

_fixtures/issue3548.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+)
+
+type Thing struct {
+	str string
+}
+
+func (d *Thing) Test() bool {
+	return d != nil
+}
+
+func callit(f func()) {
+	f()
+}
+
+func main() {
+	cases := []struct {
+		name  string
+		thing Thing
+	}{
+		{
+			name:  "Success",
+			thing: Thing{str: "hello"},
+		},
+	}
+
+	for _, c := range cases {
+		callit(func() {
+			fmt.Println("hello", c.thing.Test())
+		})
+	}
+}

pkg/proc/variables_test.go

@@ -1722,3 +1722,23 @@ func TestBadUnsafePtr(t *testing.T) {
 		}
 	})
 }
+
+func TestCapturedVariable(t *testing.T) {
+	// Checks that variables captured by a closure (that are not pointers) are
+	// readable. See issue #3548.
+	// This was broken in Go 1.21 due to a compiler bug.
+	if goversion.VersionAfterOrEqual(runtime.Version(), 1, 21) && !goversion.VersionAfterOrEqual(runtime.Version(), 1, 22) {
+		t.Skip("broken")
+	}
+	withTestProcess("issue3548", t, func(p *proc.Target, grp *proc.TargetGroup, fixture protest.Fixture) {
+		setFileBreakpoint(p, t, fixture.Source, 32)
+		assertNoError(grp.Continue(), t, "Continue()")
+		v := evalVariable(p, t, "c")
+		assertVariable(t, v, varTest{
+			name:         "c",
+			preserveName: true,
+			value:        "struct { main.name string; main.thing main.Thing } {name: \"Success\", thing: main.Thing {str: \"hello\"}}",
+			varType:      "struct { main.name string; main.thing main.Thing }",
+		})
+	})
+}