Fix "up-to-date" logic.

TODO.md

@@ -1,5 +1,6 @@
 
 # Short-term
+    * Expand ${foo}.
     * Unit tests.
     * Expanding regex matches in targets.
     * Dummy rule for multiple explicit targets
@@ -14,7 +15,4 @@
     * An attribute to demand n processors for a particular rule. This way
       resource hog rules can be run on their own without disabling parallel
       make.
-    * A switch that prints the rules that will be executed and prompts to user
-      to do so. I often find myself doing `mk -n` before `mk` to make sure my
-      rules aren't bogus.
 

graph.go

@@ -29,6 +29,7 @@ type nodeStatus int
 const (
 	nodeStatusReady nodeStatus = iota
 	nodeStatusStarted
+	nodeStatusNop
 	nodeStatusDone
 	nodeStatusFailed
 )

mk.go

@@ -90,6 +90,7 @@ func mkNode(g *graph, u *node, dryrun bool) {
 			wd, _ := os.Getwd()
 			mkError(fmt.Sprintf("don't know how to make %s in %s\n", u.name, wd))
 		}
+		finalstatus = nodeStatusNop
 		return
 	}
 
@@ -118,9 +119,6 @@ func mkNode(g *graph, u *node, dryrun bool) {
 	e.r.mutex.Lock()
 	for i := range prereqs {
 		prereqs[i].mutex.Lock()
-		// needs to be built?
-		u.updateTimestamp()
-		if !prereqs[i].exists || rebuildall || (u.exists && u.t.Before(prereqs[i].t)) {
 		switch prereqs[i].status {
 		case nodeStatusReady:
 			go mkNode(g, prereqs[i], dryrun)
@@ -129,7 +127,6 @@ func mkNode(g *graph, u *node, dryrun bool) {
 			prereqs[i].listeners = append(prereqs[i].listeners, prereqstat)
 			pending++
 		}
-		}
 		prereqs[i].mutex.Unlock()
 	}
 	e.r.mutex.Unlock()
@@ -143,13 +140,36 @@ func mkNode(g *graph, u *node, dryrun bool) {
 		}
 	}
 
+	uptodate := true
+	if !e.r.attributes.virtual {
+		u.updateTimestamp()
+		if u.exists {
+			for i := range prereqs {
+				if u.t.Before(prereqs[i].t) || prereqs[i].status == nodeStatusDone {
+					uptodate = false
+				}
+			}
+		} else {
+			uptodate = false
+		}
+	} else {
+		uptodate = false
+	}
+
+	if rebuildall {
+		uptodate = false
+	}
+
 	// execute the recipe, unless the prereqs failed
-	if finalstatus != nodeStatusFailed && len(e.r.recipe) > 0 {
+	if !uptodate && finalstatus != nodeStatusFailed && len(e.r.recipe) > 0 {
 		reserveSubproc()
 		if !dorecipe(u.name, u, e, dryrun) {
 			finalstatus = nodeStatusFailed
 		}
+		u.updateTimestamp()
 		finishSubproc()
+	} else if finalstatus != nodeStatusFailed {
+		finalstatus = nodeStatusNop
 	}
 }