genbindings: replace LinuxOnly with generic cpp/go requirements

cmd/genbindings/config-allowlist.go

@@ -638,13 +638,15 @@ func ApplyQuirks(packageName, className string, mm *CppMethod) {
 
 	if mm.ReturnType.GetQtCppType().ParameterType == "Q_PID" {
 		// int64 on Linux, _PROCESS_INFORMATION* on Windows
-		mm.LinuxOnly = true
+		mm.RequireCpp = addr("defined(Q_OS_LINUX)")
+		mm.RequireGOOS = addr("linux")
 	}
 
 	if mm.ReturnType.GetQtCppType().ParameterType == "QSocketDescriptor::DescriptorType" ||
 		(len(mm.Parameters) > 0 && mm.Parameters[0].GetQtCppType().ParameterType == "QSocketDescriptor::DescriptorType") {
 		// uintptr_t-compatible on Linux, void* on Windows
-		mm.LinuxOnly = true
+		mm.RequireCpp = addr("defined(Q_OS_LINUX)")
+		mm.RequireGOOS = addr("linux")
 	}
 
 	if className == "QArrayData" && mm.MethodName == "needsDetach" && mm.IsConst {

cmd/genbindings/emitcabi.go

@@ -1156,11 +1156,9 @@ extern "C" {
 				cabiClassName(c.ClassName) + "* " + cabiNewName(c, i) + "(" + emitParametersCabiConstructor(&c, &ctor) + ") {\n",
 			)
 
-			if ctor.LinuxOnly {
+			if ctor.RequireCpp != nil {
 				ret.WriteString(
-					"#ifndef Q_OS_LINUX\n" +
+					"#if " + *ctor.RequireCpp + "\n",
-						"\treturn nullptr;\n" +
-						"#else\n",
 				)
 			}
 
@@ -1169,8 +1167,10 @@ extern "C" {
 					"\treturn new " + cppClassName + "(" + forwarding + ");\n",
 			)
 
-			if ctor.LinuxOnly {
+			if ctor.RequireCpp != nil {
 				ret.WriteString(
+					"#else\n" +
+						"\treturn nullptr;\n" +
 						"#endif\n",
 				)
 			}
@@ -1232,15 +1232,15 @@ extern "C" {
 				callTarget = "(*self " + operator + " " + forwarding + ")"
 			}
 
-			if m.LinuxOnly {
+			if m.RequireCpp != nil {
 				ret.WriteString(fmt.Sprintf(
 					"%s %s_%s(%s) {\n"+
-						"#ifdef Q_OS_LINUX\n"+
+						"#if "+*m.RequireCpp+"\n"+
 						"%s"+
 						"%s"+
 						"#else\n"+
-						"\t%s _ret_invalidOS;\n"+
+						"\t%s _ret_unavailable;\n"+
-						"\treturn _ret_invalidOS;\n"+
+						"\treturn _ret_unavailable;\n"+
 						"#endif\n"+
 						"}\n"+
 						"\n",

cmd/genbindings/emitgo.go

@@ -899,10 +899,10 @@ import "C"
 				`,
 			)
 
-			if ctor.LinuxOnly {
+			if ctor.RequireGOOS != nil {
 				gfs.imports["runtime"] = struct{}{}
 				ret.WriteString(`
-					if runtime.GOOS != "linux" {
+					if runtime.GOOS != "` + *ctor.RequireGOOS + `" {
 						panic("Unsupported OS")
 					}
 				`)
@@ -941,10 +941,10 @@ import "C"
 
 			ret.WriteString(`
 			func ` + receiverAndMethod + `(` + gfs.emitParametersGo(m.Parameters) + `) ` + returnTypeDecl + ` {`)
-			if m.LinuxOnly {
+			if m.RequireGOOS != nil {
 				gfs.imports["runtime"] = struct{}{}
 				ret.WriteString(`
-				if runtime.GOOS != "linux" {
+				if runtime.GOOS != "` + *m.RequireGOOS + `" {
 					panic("Unsupported OS")
 				}
 				`)

cmd/genbindings/intermediate.go

@@ -254,7 +254,8 @@ type CppMethod struct {
 	HiddenParams       []CppParameter // Populated if there is an overload with more parameters
 
 	// Special quirks
-	LinuxOnly                bool
+	RequireGOOS              *string // constructs a `if runtime.GOOS = {foo}` block in the Go side, no effect on CABI / C++ sides
+	RequireCpp               *string // constructs a `#if {foo}` preprocessor block in the C++ side, no effect on Go / CABI sides
 	BecomesNonConstInVersion *string // "6,7"
 }