Update status on edge finished

In the terminal, when an edge finishes update the status to display the first started (longest running) action.
Usually this will be immediately overwritten with the next started action but if there is a bottleneck in the build or
if it is reaching the end, this ensures that the console displays status of a build that is actually running and not
one that has completed.
This ensures that the user attributes any delay to the (or an) action that is actually causing the slowdown and not
unfairly to an action that has already finished just because it happened to be the last started.

To make this clear, also change the default NINJA_STATUS to include current actual parallelism level - this will
reduce from number of cores to 1 as the bottleneck or end of build approaches.

Implementation stores currently running nodes in a deque, with NULL for interior completed nodes. This should be
fairly efficient and allows future extension to e.g. display multiple parallel action names, as in ninja-build#2249 and @orgads
prototype for ninja-build#111.

Partially resolves ninja-build#111 (should be enough for most purposes).

src/status.cc

@@ -37,8 +37,12 @@ StatusPrinter::StatusPrinter(const BuildConfig& config)
     printer_.set_smart_terminal(false);
 
   progress_status_format_ = getenv("NINJA_STATUS");
-  if (!progress_status_format_)
-    progress_status_format_ = "[%f/%t] ";
+  if (!progress_status_format_) {
+    if (printer_.is_smart_terminal())
+      progress_status_format_ = "[%f*%r/%t] ";
+    else
+      progress_status_format_ = "[%f/%t] ";
+  }
 }
 
 void StatusPrinter::PlanHasTotalEdges(int total) {
@@ -50,6 +54,8 @@ void StatusPrinter::BuildEdgeStarted(const Edge* edge,
   ++started_edges_;
   ++running_edges_;
   time_millis_ = start_time_millis;
+  if (printer_.is_smart_terminal())
+    edges_.push_back(edge);
 
   if (edge->use_console() || printer_.is_smart_terminal())
     PrintStatus(edge, start_time_millis);
@@ -63,13 +69,20 @@ void StatusPrinter::BuildEdgeFinished(Edge* edge, int64_t end_time_millis,
   time_millis_ = end_time_millis;
   ++finished_edges_;
 
+  if (printer_.is_smart_terminal()) {
+    *std::find(edges_.begin(), edges_.end(), edge) = NULL;
+    while (!edges_.empty() && edges_.front() == NULL)
+      edges_.pop_front();
+  }
+
   if (edge->use_console())
     printer_.SetConsoleLocked(false);
 
   if (config_.verbosity == BuildConfig::QUIET)
     return;
 
-  if (!edge->use_console())
+  if (!edge->use_console()
+      && (!printer_.is_smart_terminal() || !success || !output.empty()))
     PrintStatus(edge, end_time_millis);
 
   --running_edges_;
@@ -118,6 +131,9 @@ void StatusPrinter::BuildEdgeFinished(Edge* edge, int64_t end_time_millis,
     _setmode(_fileno(stdout), _O_TEXT);  // End Windows extra CR fix
 #endif
   }
+
+  if (printer_.is_smart_terminal() && !edges_.empty())
+    PrintStatus(edges_.front(), end_time_millis);
 }
 
 void StatusPrinter::BuildLoadDyndeps() {

src/status.h

@@ -15,7 +15,9 @@
 #ifndef NINJA_STATUS_H_
 #define NINJA_STATUS_H_
 
+#include <deque>
 #include <map>
+#include <queue>
 #include <string>
 
 #include "build.h"
@@ -72,6 +74,7 @@ struct StatusPrinter : Status {
 
   int started_edges_, finished_edges_, total_edges_, running_edges_;
   int64_t time_millis_;
+  std::deque<const Edge*> edges_;
 
   /// Prints progress output.
   LinePrinter printer_;