Migrate explanation printing from StatusPrinter to Explanations

It makes more sense to live in the latter.

Suggested-by: David 'Digit' Turner <digit+github@google.com>

src/build.cc

@@ -604,7 +604,7 @@ Builder::Builder(State* state, const BuildConfig& config, BuildLog* build_log,
                  Status* status, int64_t start_time_millis)
     : state_(state), config_(config), plan_(this), status_(status),
       start_time_millis_(start_time_millis), disk_interface_(disk_interface),
-      explanations_(g_explaining ? new Explanations() : nullptr),
+      explanations_(g_explaining ? new Explanations(status) : nullptr),
       scan_(state, build_log, deps_log, disk_interface,
             &config_.depfile_parser_options, explanations_.get()) {
   lock_file_path_ = ".ninja_lock";

src/explanations.cc

@@ -21,6 +21,26 @@
 #include <unordered_map>
 #include <vector>
 
+#include "graph.h"
+#include "status_printer.h"
+
+namespace {
+void Explain(const char* msg, va_list ap) {
+  fputs("ninja explain: ", stderr);
+  vfprintf(stderr, msg, ap);
+  fputs("\n", stderr);
+}
+
+void Explain(const char* msg, ...) {
+  va_list ap;
+  va_start(ap, msg);
+  Explain(msg, ap);
+  va_end(ap);
+}
+}  // anonymous namespace
+
+Explanations::Explanations(Status* status) : status_(status) {}
+
 void Explanations::Record(const void* item, const char* fmt, ...) {
   va_list args;
   va_start(args, fmt);
@@ -34,6 +54,24 @@ void Explanations::RecordArgs(const void* item, const char* fmt, va_list args) {
   map_[item].emplace_back(buffer);
 }
 
+void Explanations::ExplainEdge(const Edge* edge) {
+  // Collect all explanations for the current edge's outputs.
+  std::vector<std::string> explanations;
+  for (Node* output : edge->outputs_) {
+    this->LookupAndAppend(output, &explanations);
+  }
+  if (!explanations.empty()) {
+    if (status_) {
+      // Start a new line so that the first explanation
+      // does not append to the status line.
+      status_->NewLine();
+    }
+    for (const auto& exp : explanations) {
+      Explain("%s", exp.c_str());
+    }
+  }
+}
+
 void Explanations::LookupAndAppend(const void* item,
                                    std::vector<std::string>* out) {
   auto it = map_.find(item);

src/explanations.h

@@ -20,23 +20,32 @@
 #include <unordered_map>
 #include <vector>
 
+struct Edge;
+struct Status;
+
 /// A class used to record a list of explanation strings associated
 /// with a given 'item' pointer. This is used to implement the
 /// `-d explain` feature.
 struct Explanations {
  public:
+  Explanations(Status* status = nullptr);
+
   /// Record an explanation for |item| if this instance is enabled.
   void Record(const void* item, const char* fmt, ...);
 
   /// Same as Record(), but uses a va_list to pass formatting arguments.
   void RecordArgs(const void* item, const char* fmt, va_list args);
 
+  /// Print recorded explanations for an edge.
+  void ExplainEdge(const Edge* edge);
+
   /// Lookup the explanations recorded for |item|, and append them
   /// to |*out|, if any.
   void LookupAndAppend(const void* item, std::vector<std::string>* out);
 
  private:
   std::unordered_map<const void*, std::vector<std::string>> map_;
+  Status* status_;
 };
 
 /// Convenience wrapper for an Explanations pointer, which can be null

src/status.h

@@ -40,6 +40,9 @@ struct Status {
   /// (which is the default).
   virtual void SetExplanations(Explanations*) = 0;
 
+  /// Start a new line so that new output does not append to the status line.
+  virtual void NewLine() = 0;
+
   virtual void Info(const char* msg, ...) = 0;
   virtual void Warning(const char* msg, ...) = 0;
   virtual void Error(const char* msg, ...) = 0;

src/status_printer.cc

@@ -407,19 +407,7 @@ string StatusPrinter::FormatProgressStatus(const char* progress_status_format,
 
 void StatusPrinter::PrintStatus(const Edge* edge, int64_t time_millis) {
   if (explanations_) {
-    // Collect all explanations for the current edge's outputs.
-    std::vector<std::string> explanations;
-    for (Node* output : edge->outputs_) {
-      explanations_->LookupAndAppend(output, &explanations);
-    }
-    if (!explanations.empty()) {
-      // Start a new line so that the first explanation does not append to the
-      // status line.
-      printer_.PrintOnNewLine("");
-      for (const auto& exp : explanations) {
-        fprintf(stderr, "ninja explain: %s\n", exp.c_str());
-      }
-    }
+    explanations_->ExplainEdge(edge);
   }
 
   if (config_.verbosity == BuildConfig::QUIET
@@ -441,6 +429,10 @@ void StatusPrinter::PrintStatus(const Edge* edge, int64_t time_millis) {
                  force_full_command ? LinePrinter::FULL : LinePrinter::ELIDE);
 }
 
+void StatusPrinter::NewLine() {
+  printer_.PrintOnNewLine("");
+}
+
 void StatusPrinter::Warning(const char* msg, ...) {
   va_list ap;
   va_start(ap, msg);

src/status_printer.h

@@ -37,6 +37,7 @@ struct StatusPrinter : Status {
   void BuildStarted() override;
   void BuildFinished() override;
 
+  void NewLine() override;
   void Info(const char* msg, ...) override;
   void Warning(const char* msg, ...) override;
   void Error(const char* msg, ...) override;