internal/rosa: expose in-place behaviour in generic helper

This change also combines the createDir and wantsDir methods, and replaces the non-inplace target of the generic helper with a deterministic path.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -397,13 +397,11 @@ type Helper interface {
 	// scriptEarly returns the helper-specific segment of cure script that goes
 	// before the cd statement.
 	scriptEarly() string
-	// createDir returns whether the path returned by wantsDir should be created.
-	createDir() bool
 	// wantsDir returns the directory to enter before script.
 	//
 	// The zero value implies source directory if [PackageAttr.ScriptEarly] is
 	// also empty. The special value helperInPlace omits the cd statement.
-	wantsDir() string
+	wantsDir() (pathname string, create bool)
 	// script returns the helper-specific segment of cure script.
 	script(t Toolchain, name string) string
 }
@@ -527,7 +525,7 @@ mv '/usr/src/` + rn + `' '/usr/src/` + name + `'
 `
 	}
 
-	dir := helper.wantsDir()
+	dir, create := helper.wantsDir()
 	helperScriptEarly := helper.scriptEarly()
 	if attr.EnterSource ||
 		dir == "" ||
@@ -539,7 +537,7 @@ cd '/usr/src/` + name + `/'
 	}
 	scriptEarly += attr.ScriptEarly + helperScriptEarly
 	if dir != "" && dir != helperInPlace {
-		if helper.createDir() {
+		if create {
 			scriptEarly += "\nmkdir -p " + dir
 		}
 		scriptEarly += "\ncd " + dir + "\n"
@@ -568,8 +566,8 @@ cd '/usr/src/` + name + `/'
 // one-off build scripts too specific to fit into any other [Helper]
 // implementation, but can still benefit from [Toolchain.NewPackage].
 type GenericHelper struct {
-	// Whether to create and enter a directory in TMPDIR.
-	EnterTemp bool
+	// Remain in current directory.
+	InPlace bool
 
 	// Concatenated for [Toolchain].
 	Build, Check, Install string
@@ -589,15 +587,12 @@ func (*GenericHelper) wantsWrite() bool { return false }
 // scriptEarly returns the zero value.
 func (*GenericHelper) scriptEarly() string { return "" }
 
-// createDir returns false.
-func (*GenericHelper) createDir() bool { return false }
-
-// wantsDir requests a new directory in TMPDIR, or the source directory otherwise.
-func (attr *GenericHelper) wantsDir() string {
-	if attr != nil && attr.EnterTemp {
-		return `"$(mktemp -d)"`
+// wantsDir requests a new directory, or omits the cd statement if InPlace.
+func (attr *GenericHelper) wantsDir() (string, bool) {
+	if attr == nil || !attr.InPlace {
+		return "/cure/", true
 	}
-	return ""
+	return helperInPlace, false
 }
 
 // script concatenates specified segments.