compiler: support //go:linknamestd pragma

Go 1.27 introduced the //go:linknamestd directive, a standard-library
variant of //go:linkname that does not require importing "unsafe". The
iter package switched to it for referencing runtime.newcoro and
runtime.coroswitch, which caused "linker could not find symbol
iter.newcoro / iter.coroswitch" errors when building with Go 1.27.

Handle //go:linknamestd the same as //go:linkname, bypassing the unsafe
import requirement, and add test coverage in the pragma compiler test.

Signed-off-by: deadprogram <ron@hybridgroup.com>

Author: deadprogram

compiler/symbol.go

@@ -443,15 +443,18 @@ func (c *compilerContext) parsePragmas(info *functionInfo, f *ssa.Function) {
 			info.inline = inlineHint
 		case "//go:noinline":
 			info.inline = inlineNone
-		case "//go:linkname":
+		case "//go:linkname", "//go:linknamestd":
 			if len(parts) != 3 || parts[1] != f.Name() {
 				continue
 			}
 			// Only enable go:linkname when the package imports "unsafe".
 			// This is a slightly looser requirement than what gc uses: gc
 			// requires the file to import "unsafe", not the package as a
 			// whole.
-			if hasUnsafeImport(f.Pkg.Pkg) {
+			// //go:linknamestd is a Go 1.27+ variant used inside the standard
+			// library (for example by the iter package) that does not require
+			// importing "unsafe".
+			if parts[0] == "//go:linknamestd" || hasUnsafeImport(f.Pkg.Pkg) {
 				info.linkName = parts[2]
 			}
 		case "//go:section":

compiler/testdata/pragma.go

@@ -35,6 +35,12 @@ func withLinkageName1() {
 //go:linkname withLinkageName2 somepkg.someFunction2
 func withLinkageName2()
 
+// Import a function from a different package using go:linknamestd (the standard
+// library variant of go:linkname introduced in Go 1.27).
+//
+//go:linknamestd withLinkageNameStd somepkg.someFunctionStd
+func withLinkageNameStd()
+
 // Function has an 'inline hint', similar to the inline keyword in C.
 //
 //go:inline

compiler/testdata/pragma.ll

@@ -33,6 +33,8 @@ entry:
 
 declare void @somepkg.someFunction2(ptr) #0
 
+declare void @somepkg.someFunctionStd(ptr) #0
+
 ; Function Attrs: inlinehint nounwind
 define hidden void @main.inlineFunc(ptr %context) unnamed_addr #3 {
 entry: