Move procid to dynamic facts render

Based on cl/504066914, this generates the proper procid offsets at build time.

Package facts needs an update to properly skip underscore imports, which don't
have facts for some reason (because they are unnamed?).

Drop use of runtime.getprocid given that these generated code is pretty solid.

PiperOrigin-RevId: 504926257

pkg/procid/BUILD

@@ -1,13 +1,29 @@
-load("//tools:defs.bzl", "go_library", "go_test")
+load("//tools:defs.bzl", "arch_genrule", "go_library", "go_test", "select_arch")
+load("//tools/nogo:defs.bzl", "nogo_facts")
 
 package(licenses = ["notice"])
 
+nogo_facts(
+    name = "procid_impl",
+    srcs = ["procid.go"],
+    output = "procid_impl.s",
+    template = select_arch(
+        amd64 = "procid_amd64.s",
+        arm64 = "procid_arm64.s",
+    ),
+)
+
+arch_genrule(
+    name = "procid_impl_arch",
+    src = ":procid_impl",
+    template = "procid_impl_%s.s",
+)
+
 go_library(
     name = "procid",
     srcs = [
         "procid.go",
-        "procid_amd64.s",
-        "procid_arm64.s",
+        ":procid_impl_arch",
     ],
     visibility = ["//visibility:public"],
 )

pkg/procid/procid.go

@@ -12,12 +12,16 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build go1.1
-// +build go1.1
-
 // Package procid provides a way to get the current system thread identifier.
 package procid
 
+import (
+	"runtime"
+)
+
+// Dummy references for facts.
+const _ = runtime.Compiler
+
 // Current returns the current system thread identifier.
 //
 // Precondition: This should only be called with the runtime OS thread locked.

pkg/procid/procid_amd64.s

@@ -12,22 +12,19 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build amd64 && go1.8 && !go1.21 && go1.1
-// +build amd64,go1.8,!go1.21,go1.1
-
-// //go:linkname directives type-checked by checklinkname. Any other
-// non-linkname assumptions outside the Go 1 compatibility guarantee should
-// have an accompanied vet check or version guard build tag.
+//go:build amd64
+// +build amd64
 
 #include "textflag.h"
 
+#define M_OFFSET {{ .import.runtime.g.m.Offset }}
+#define PROCID_OFFSET {{ .import.runtime.m.procid.Offset }}
+
 TEXT ·Current(SB),NOSPLIT,$0-8
-	// The offset specified here is the m_procid offset for Go1.8+.
-	// Changes to this offset should be caught by the tests, and major
-	// version changes require an explicit tag change above.
+	// procid is in getg().m.procid.
 	MOVQ TLS, AX
 	MOVQ 0(AX)(TLS*1), AX
-	MOVQ 48(AX), AX // g_m (may change in future versions)
-	MOVQ 72(AX), AX // m_procid (may change in future versions)
+	MOVQ M_OFFSET(AX), AX // gp.m
+	MOVQ PROCID_OFFSET(AX), AX // mp.procid
 	MOVQ AX, ret+0(FP)
 	RET

pkg/procid/procid_arm64.s

@@ -12,21 +12,18 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build arm64 && go1.8 && !go1.21 && go1.1
-// +build arm64,go1.8,!go1.21,go1.1
-
-// //go:linkname directives type-checked by checklinkname. Any other
-// non-linkname assumptions outside the Go 1 compatibility guarantee should
-// have an accompanied vet check or version guard build tag.
+//go:build arm64
+// +build arm64
 
 #include "textflag.h"
 
+#define M_OFFSET {{ .import.runtime.g.m.Offset }}
+#define PROCID_OFFSET {{ .import.runtime.m.procid.Offset }}
+
 TEXT ·Current(SB),NOSPLIT,$0-8
-	// The offset specified here is the m_procid offset for Go1.8+.
-	// Changes to this offset should be caught by the tests, and major
-	// version changes require an explicit tag change above.
+	// procid is in getg().m.procid.
 	MOVD g, R0      // g
-	MOVD 48(R0), R0 // g_m (may change in future versions)
-	MOVD 72(R0), R0 // m_procid (may change in future versions)
+	MOVD M_OFFSET(R0), R0 // gp.m
+	MOVD PROCID_OFFSET(R0), R0 // mp.procid
 	MOVD R0, ret+0(FP)
 	RET

tools/nogo/facts/facts.go

@@ -230,6 +230,13 @@ func (b *Bundle) Package(pkg *types.Package) (*Package, error) {
 		return facts, nil
 	}
 
+	if b.reader == nil {
+		// Nothing available.
+		//
+		// N.B. some bundles contain only cached packages.
+		return nil, nil
+	}
+
 	// Find based on the reader.
 	for _, f := range b.reader.File {
 		if f.Name != pkg.Path() {
@@ -368,6 +375,9 @@ func Resolve(pkg *types.Package, localFacts *Package, allFacts *Bundle, allFactN
 		if err != nil {
 			return nil, err
 		}
+		if importFacts == nil {
+			continue
+		}
 		r.walkScope(append(names, "import", importPkg.Name()), importPkg.Scope(), importFacts, allFactNames)
 	}
 	return r, nil