Issue #546 : collectgarbage honors its option and returns a value

_glua-tests/base.lua

@@ -46,3 +46,14 @@ local ok, a, b = xpcall(function()
      return err .. "!", "b"
   end)
 assert(not ok and string.find(a, "error!!") and b == nil)
+
+-- collectgarbage options, as in Lua 5.1 (#546)
+assert(collectgarbage() == 0)
+assert(collectgarbage("collect") == 0)
+local kb = collectgarbage("count")
+assert(type(kb) == "number" and kb > 0)
+assert(type(collectgarbage("step")) == "boolean")
+assert(collectgarbage("stop") == 0 and collectgarbage("restart") == 0)
+assert(collectgarbage("setpause", 150) == 200 and collectgarbage("setpause", 200) == 150)
+assert(collectgarbage("setstepmul", 300) == 200 and collectgarbage("setstepmul", 200) == 300)
+assert(not pcall(collectgarbage, "nope"))

_state.go

@@ -543,6 +543,8 @@ func newGlobal() *Global {
 		Global:     newLTable(0, 64),
 		builtinMts: make(map[int]LValue),
 		tempFiles:  make([]*os.File, 0, 10),
+		gcPause:    200, // Lua 5.1 defaults
+		gcStepMul:  200,
 	}
 }
 

baselib.go

@@ -64,8 +64,33 @@ func baseAssert(L *LState) int {
 }
 
 func baseCollectGarbage(L *LState) int {
-	runtime.GC()
-	return 0
+	switch opt := L.OptString(1, "collect"); opt {
+	case "collect":
+		runtime.GC()
+		L.Push(LNumber(0))
+	case "count":
+		// Kbytes in use by the Go heap (the Lua state has no heap of its own).
+		var ms runtime.MemStats
+		runtime.ReadMemStats(&ms)
+		L.Push(LNumber(float64(ms.HeapAlloc) / 1024))
+	case "step":
+		runtime.GC()
+		L.Push(LTrue)
+	case "stop", "restart":
+		// The Go collector cannot be stopped for one state.
+		L.Push(LNumber(0))
+	case "setpause":
+		prev := L.G.gcPause
+		L.G.gcPause = L.OptInt(2, 0)
+		L.Push(LNumber(prev))
+	case "setstepmul":
+		prev := L.G.gcStepMul
+		L.G.gcStepMul = L.OptInt(2, 0)
+		L.Push(LNumber(prev))
+	default:
+		L.ArgError(1, "invalid option '"+opt+"'")
+	}
+	return 1
 }
 
 func baseDoFile(L *LState) int {

state.go

@@ -643,6 +643,8 @@ func newGlobal() *Global {
 		Global:     newLTable(0, 64),
 		builtinMts: make(map[int]LValue),
 		tempFiles:  make([]*os.File, 0, 10),
+		gcPause:    200, // Lua 5.1 defaults
+		gcStepMul:  200,
 	}
 }
 

value.go

@@ -174,6 +174,8 @@ type Global struct {
 	builtinMts map[int]LValue
 	tempFiles  []*os.File
 	gccount    int32
+	gcPause    int // collectgarbage("setpause"): kept and returned, no effect on the Go collector
+	gcStepMul  int // collectgarbage("setstepmul"): idem
 }
 
 type LState struct {