Reliable ETA and progress percentage.

This has been bugging me for *years*. :)
Count of finished edges isn't a great statistic, it isn't
really obvious if LLVM will take 8 minues to build, or 10 minutes.

But, it's actually pretty straight-forward to get some
more useful information. We already know how much time each edge
has taken, so we could just do the dumb thing, and assume that
every edge in the plan takes the same amount of time.

Or, we can do better. `.ninja_log` already contains
the historical data on how long each edge took to produce it's outs,
so we simply need to ensure that we populate edges with that info,
and then we can greatly improve our predictions.
The math is pretty simple i think.

This is largely a port of a similar change i did to LLVM LIT:
https://reviews.llvm.org/D99073

With this, i get something quite lovely:
```
llvm-project/build-Clang12$ NINJA_STATUS="[%f/%t %p %P][%w + %W] " /repositories/ninja/build-Clang-debug/ninja opt
[288/2527  11%   4%][00:27 + 08:52] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/AppendingTypeTableBuilder.cpp.o
```

I hope people will find this useful, and it could be merged.

doc/manual.asciidoc

@@ -204,7 +204,11 @@ Several placeholders are available:
 `%o`:: Overall rate of finished edges per second
 `%c`:: Current rate of finished edges per second (average over builds
 specified by `-j` or its default)
-`%e`:: Elapsed time in seconds.  _(Available since Ninja 1.2.)_
+`%e`:: Elapsed time in seconds. _(Available since Ninja 1.2.)_
+`%E`:: Remaining time (ETA) in seconds. _(Available since Ninja 1.12.0.)_
+`%w`:: Elapsed time in [h:]mm:ss format. _(Available since Ninja 1.12.)_
+`%W`:: Remaining time (ETA) in [h:]mm:ss format. _(Available since Ninja 1.12.0.)_
+`%P`:: The percentage (in ppp% format) of time elapsed out of predicted total runtime. _(Available since Ninja 1.12.0.)_
 `%%`:: A plain `%` character.
 
 The default progress status is `"[%f/%t] "` (note the trailing space

src/build.cc

@@ -144,8 +144,11 @@ bool Plan::AddSubTarget(const Node* node, const Node* dependent, string* err,
 
 void Plan::EdgeWanted(const Edge* edge) {
   ++wanted_edges_;
-  if (!edge->is_phony())
+  if (!edge->is_phony()) {
     ++command_edges_;
+    if (builder_)
+      builder_->status_->EdgeAddedToPlan(edge);
+  }
 }
 
 Edge* Plan::FindWork() {
@@ -294,8 +297,11 @@ bool Plan::CleanNode(DependencyScan* scan, Node* node, string* err) {
 
         want_e->second = kWantNothing;
         --wanted_edges_;
-        if (!(*oe)->is_phony())
+        if (!(*oe)->is_phony()) {
           --command_edges_;
+          if (builder_)
+            builder_->status_->EdgeRemovedFromPlan(*oe);
+        }
       }
     }
   }
@@ -607,7 +613,6 @@ bool Builder::AlreadyUpToDate() const {
 bool Builder::Build(string* err) {
   assert(!AlreadyUpToDate());
 
-  status_->PlanHasTotalEdges(plan_.command_edge_count());
   int pending_commands = 0;
   int failures_allowed = config_.failures_allowed;
 
@@ -780,8 +785,8 @@ bool Builder::FinishCommand(CommandRunner::Result* result, string* err) {
   end_time_millis = GetTimeMillis() - start_time_millis_;
   running_edges_.erase(it);
 
-  status_->BuildEdgeFinished(edge, end_time_millis, result->success(),
-                             result->output);
+  status_->BuildEdgeFinished(edge, start_time_millis, end_time_millis,
+                             result->success(), result->output);
 
   // The rest of this function only applies to successful commands.
   if (!result->success()) {
@@ -821,10 +826,6 @@ bool Builder::FinishCommand(CommandRunner::Result* result, string* err) {
     }
     if (node_cleaned) {
       record_mtime = edge->command_start_time_;
-
-      // The total number of edges in the plan may have changed as a result
-      // of a restat.
-      status_->PlanHasTotalEdges(plan_.command_edge_count());
     }
   }
 
@@ -938,8 +939,5 @@ bool Builder::LoadDyndeps(Node* node, string* err) {
   if (!plan_.DyndepsLoaded(&scan_, node, ddf, err))
     return false;
 
-  // New command edges may have been added to the plan.
-  status_->PlanHasTotalEdges(plan_.command_edge_count());
-
   return true;
 }

src/build_test.cc

@@ -2197,11 +2197,28 @@ TEST_F(BuildTest, DepsGccWithEmptyDepfileErrorsOut) {
   ASSERT_EQ(1u, command_runner_.commands_ran_.size());
 }
 
-TEST_F(BuildTest, StatusFormatElapsed) {
+TEST_F(BuildTest, StatusFormatElapsed_e) {
   status_.BuildStarted();
   // Before any task is done, the elapsed time must be zero.
-  EXPECT_EQ("[%/e0.000]",
-            status_.FormatProgressStatus("[%%/e%e]", 0));
+  EXPECT_EQ("[%/e0.000]", status_.FormatProgressStatus("[%%/e%e]", 0));
+}
+
+TEST_F(BuildTest, StatusFormatElapsed_w) {
+  status_.BuildStarted();
+  // Before any task is done, the elapsed time must be zero.
+  EXPECT_EQ("[%/e00:00]", status_.FormatProgressStatus("[%%/e%w]", 0));
+}
+
+TEST_F(BuildTest, StatusFormatETA) {
+  status_.BuildStarted();
+  // Before any task is done, the ETA time must be unknown.
+  EXPECT_EQ("[%/E?]", status_.FormatProgressStatus("[%%/E%E]", 0));
+}
+
+TEST_F(BuildTest, StatusFormatTimeProgress) {
+  status_.BuildStarted();
+  // Before any task is done, the percentage of elapsed time must be zero.
+  EXPECT_EQ("[%/p  0%]", status_.FormatProgressStatus("[%%/p%p]", 0));
 }
 
 TEST_F(BuildTest, StatusFormatReplacePlaceholder) {

src/graph.h

@@ -250,6 +250,10 @@ struct Edge {
   bool is_phony() const;
   bool use_console() const;
   bool maybe_phonycycle_diagnostic() const;
+
+  // Historical info: how long did this edge take last time,
+  // as per .ninja_log, if known? Defaults to -1 if unknown.
+  int64_t prev_elapsed_time_millis = -1;
 };
 
 struct EdgeCmp {

src/ninja.cc

@@ -156,6 +156,10 @@ struct NinjaMain : public BuildLogUser {
   /// @return true if the manifest was rebuilt.
   bool RebuildManifest(const char* input_file, string* err, Status* status);
 
+  /// For each edge, lookup in build log how long it took last time,
+  /// and record that in the edge itself. It will be used for ETA predicton.
+  void ParsePreviousElapsedTimes();
+
   /// Build the targets listed on the command line.
   /// @return an exit code.
   int RunBuild(int argc, char** argv, Status* status);
@@ -289,6 +293,19 @@ bool NinjaMain::RebuildManifest(const char* input_file, string* err,
   return true;
 }
 
+void NinjaMain::ParsePreviousElapsedTimes() {
+  for (Edge* edge : state_.edges_) {
+    for (Node* out : edge->outputs_) {
+      BuildLog::LogEntry* log_entry = build_log_.LookupByOutput(out->path());
+      if (!log_entry)
+        continue;  // Maybe we'll have log entry for next output of this edge?
+      edge->prev_elapsed_time_millis =
+          log_entry->end_time - log_entry->start_time;
+      break;  // Onto next edge.
+    }
+  }
+}
+
 Node* NinjaMain::CollectTarget(const char* cpath, string* err) {
   string path = cpath;
   if (path.empty()) {
@@ -1588,6 +1605,8 @@ NORETURN void real_main(int argc, char** argv) {
       exit(1);
     }
 
+    ninja.ParsePreviousElapsedTimes();
+
     int result = ninja.RunBuild(argc, argv, status);
     if (g_metrics)
       ninja.DumpMetrics();