cmd/cgo: disable #cgo noescape/nocallback until Go 1.23

Go 1.21 and earlier do not understand this line, causing
"go mod vendor" of //go:build go1.22-tagged code that
uses this feature to fail.

The solution is to include the go/build change to skip over
the line in Go 1.22 (making "go mod vendor" from Go 1.22 onward
work with this change) and then wait to deploy the cgo change
until Go 1.23, at which point Go 1.21 and earlier will be unsupported.

For #56378.
Fixes #63293.

Change-Id: Ifa08b134eac5a6aa15d67dad0851f00e15e1e58b
Reviewed-on: https://go-review.googlesource.com/c/go/+/539235
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: rsc

doc/go1.22.html

@@ -39,24 +39,7 @@ <h3 id="go-command">Go command</h3>
 
 <h3 id="cgo">Cgo</h3>
 
-<p><!-- CL 497837 --> The special comment that precedes
-  <code>import</code> <code>"C"</code> may now include two
-  new <code>#cgo</code> directives.
-  <ul>
-    <li>
-      <code>#cgo</code> <code>noescape</code> <code>cFunctionName</code>
-      tells cgo that Go pointers passed to the C function
-      <code>cFunctionName</code> do not escape.
-    </li>
-    <li>
-      <code>#cgo</code> <code>nocallback</code> <code>cFunctionName</code>
-      tells cgo that the C function <code>cFunctionName</code> does
-      not call any Go functions.
-    </li>
-  </ul>
-  See <a href="/cmd/cgo#hdr-Optimizing_calls_of_C_code">the <code>cgo</code>
-  documentation</a> for more details.
-</p>
+<!-- CL 497837 reverted -->
 
 <h2 id="runtime">Runtime</h2>
 

src/cmd/cgo/doc.go

@@ -420,30 +420,6 @@ passing uninitialized C memory to Go code if the Go code is going to
 store pointer values in it. Zero out the memory in C before passing it
 to Go.
 
-# Optimizing calls of C code
-
-When passing a Go pointer to a C function the compiler normally ensures
-that the Go object lives on the heap. If the C function does not keep
-a copy of the Go pointer, and never passes the Go pointer back to Go code,
-then this is unnecessary. The #cgo noescape directive may be used to tell
-the compiler that no Go pointers escape via the named C function.
-If the noescape directive is used and the C function does not handle the
-pointer safely, the program may crash or see memory corruption.
-
-For example:
-
-	// #cgo noescape cFunctionName
-
-When a Go function calls a C function, it prepares for the C function to
-call back to a Go function. the #cgo nocallback directive may be used to
-tell the compiler that these preparations are not necessary.
-If the nocallback directive is used and the C function does call back into
-Go code, the program will panic.
-
-For example:
-
-	// #cgo nocallback cFunctionName
-
 # Special cases
 
 A few special C types which would normally be represented by a pointer

src/cmd/cgo/gcc.go

@@ -94,8 +94,10 @@ func (f *File) ProcessCgoDirectives() {
 				directive := fields[1]
 				funcName := fields[2]
 				if directive == "nocallback" {
+					fatalf("#cgo nocallback disabled until Go 1.23")
 					f.NoCallbacks[funcName] = true
 				} else if directive == "noescape" {
+					fatalf("#cgo noescape disabled until Go 1.23")
 					f.NoEscapes[funcName] = true
 				}
 			}

src/cmd/cgo/internal/test/test.go

@@ -117,7 +117,8 @@ int add(int x, int y) {
 
 // escape vs noescape
 
-#cgo noescape handleGoStringPointerNoescape
+// TODO(#56378): enable in Go 1.23:
+// #cgo noescape handleGoStringPointerNoescape
 void handleGoStringPointerNoescape(void *s) {}
 
 void handleGoStringPointerEscape(void *s) {}

src/cmd/cgo/internal/testerrors/testdata/notmatchedcfunction.go

@@ -5,7 +5,8 @@
 package main
 
 /*
-// ERROR MESSAGE: #cgo noescape noMatchedCFunction: no matched C function
+// TODO(#56378): change back to "#cgo noescape noMatchedCFunction: no matched C function" in Go 1.23
+// ERROR MESSAGE: #cgo noescape disabled until Go 1.23
 #cgo noescape noMatchedCFunction
 */
 import "C"

src/runtime/crash_cgo_test.go

@@ -754,6 +754,7 @@ func TestNeedmDeadlock(t *testing.T) {
 }
 
 func TestCgoNoCallback(t *testing.T) {
+	t.Skip("TODO(#56378): enable in Go 1.23")
 	got := runTestProg(t, "testprogcgo", "CgoNoCallback")
 	want := "function marked with #cgo nocallback called back into Go"
 	if !strings.Contains(got, want) {
@@ -762,6 +763,7 @@ func TestCgoNoCallback(t *testing.T) {
 }
 
 func TestCgoNoEscape(t *testing.T) {
+	t.Skip("TODO(#56378): enable in Go 1.23")
 	got := runTestProg(t, "testprogcgo", "CgoNoEscape")
 	want := "OK\n"
 	if got != want {

src/runtime/testdata/testprogcgo/cgonocallback.go

@@ -8,8 +8,7 @@ package main
 // But it do callback to go in this test, Go should crash here.
 
 /*
-#cgo nocallback runCShouldNotCallback
-
+// TODO(#56378): #cgo nocallback runCShouldNotCallback
 extern void runCShouldNotCallback();
 */
 import "C"

src/runtime/testdata/testprogcgo/cgonoescape.go

@@ -13,7 +13,7 @@ package main
 // 2. less than 100 new allocated heap objects after invoking withoutNoEscape 100 times.
 
 /*
-#cgo noescape runCWithNoEscape
+// TODO(#56378): #cgo noescape runCWithNoEscape
 
 void runCWithNoEscape(void *p) {
 }