cmd/compile: note escape of parts of closured-capture vars

Missed a case for closure calls (OCALLFUNC && indirect) in
esc.go:esccall.

Cleanup to runtime code for windows to more thoroughly hide
a technical escape.  Also made code pickier about failing
to late non-optional kernel32.dll.

Fixes #14409.

Change-Id: Ie75486a2c8626c4583224e02e4872c2875f7bca5
Reviewed-on: https://go-review.googlesource.com/20102
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/test/escape_closure.go b/test/escape_closure.go
index 4cdb06e4c5..f36073e7d0 100644
--- a/test/escape_closure.go
+++ b/test/escape_closure.go
@@ -145,3 +145,29 @@ func ClosureCallArgs15() {
 		// BAD: p should not escape here
 	}(&p) // ERROR "&p escapes to heap" "\(func literal\)\(&p\) escapes to heap"
 }
+
+func ClosureLeak1(s string) string { // ERROR "ClosureLeak1 s does not escape"
+	t := s + "YYYY"         // ERROR "escapes to heap"
+	return ClosureLeak1a(t) // ERROR "ClosureLeak1 ... argument does not escape"
+}
+
+// See #14409 -- returning part of captured var leaks it.
+func ClosureLeak1a(a ...string) string { // ERROR "leaking param: a to result ~r1 level=1"
+	return func() string { // ERROR "ClosureLeak1a func literal does not escape"
+		return a[0]
+	}()
+}
+
+func ClosureLeak2(s string) string { // ERROR "ClosureLeak2 s does not escape"
+	t := s + "YYYY"       // ERROR "escapes to heap"
+	c := ClosureLeak2a(t) // ERROR "ClosureLeak2 ... argument does not escape"
+	return c
+}
+func ClosureLeak2a(a ...string) string { // ERROR "leaking param: a to result ~r1 level=1"
+	return ClosureLeak2b(func() string { // ERROR "ClosureLeak2a func literal does not escape"
+		return a[0]
+	})
+}
+func ClosureLeak2b(f func() string) string { // ERROR "leaking param: f to result ~r1 level=1"
+	return f()
+}