From: uazo <uazo@users.noreply.github.com>
Date: Wed, 8 Dec 2021 11:08:45 +0000
Subject: Allow 'ninja -t compdb' accept one target

---
 src/ninja.cc | 64 +++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 61 insertions(+), 3 deletions(-)

diff --git a/src/ninja.cc b/src/ninja.cc
index ed004ac8f1fe1a5107db8b1f5c02c4ba957daef4..bbb79da561ddec497863230cd99ffbe98b9a76e5 100644
--- a/src/ninja.cc
+++ b/src/ninja.cc
@@ -17,6 +17,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unordered_set>
 
 #ifdef _WIN32
 #include "getopt.h"
@@ -73,6 +74,8 @@ struct Options {
 
   /// Whether phony cycles should warn or print an error.
   bool phony_cycle_should_err;
+
+  const char* user_given_target;
 };
 
 /// The Ninja main() loads up a series of data structures; various tools need
@@ -211,6 +214,7 @@ void Usage(const BuildConfig& config) {
 "  -l N     do not start new jobs if the load average is greater than N\n"
 "  -n       dry run (don't run commands but act like they succeeded)\n"
 "  -v       show all command lines while building\n"
+"  -a       generate compilation database for given target\n"
 "\n"
 "  -d MODE  enable debugging (use -d list to list modes)\n"
 "  -t TOOL  run a subtool (use -t list to list subtools)\n"
@@ -662,7 +666,56 @@ void EncodeJSONString(const char *str) {
   }
 }
 
+bool GetAllDependentEdges(Node* node, std::vector<Edge*>* depend_edges,
+                          std::unordered_set<Node*>* visited_nodes=NULL,
+                          std::unordered_set<Edge*>* visited_edges=NULL) {
+  if (visited_nodes == NULL || visited_edges == NULL) {
+    std::unordered_set<Node*> visited_nodes_;
+    std::unordered_set<Edge*> visited_edges_;
+    return GetAllDependentEdges(node, depend_edges, &visited_nodes_, &visited_edges_);
+  }
+  if (node == NULL || depend_edges == NULL) {
+    Error("Internal error");
+    return false;
+  }
+  if (visited_nodes->count(node)) {
+    return true;
+  } else {
+    visited_nodes->insert(node);
+  }
+  Edge* edge = node->in_edge();
+  // Leaf node
+  if (!edge || visited_edges->count(edge)) {
+    return true;
+  } else {
+    visited_edges->insert(edge);
+    depend_edges->push_back(edge);
+  }
+  for (Node* input_node : edge->inputs_) {
+    if (!GetAllDependentEdges(input_node, depend_edges, visited_nodes, visited_edges))
+      return false;
+  }
+  return true;
+}
+
 int NinjaMain::ToolCompilationDatabase(const Options* options, int argc, char* argv[]) {
+  std::vector<Edge*>* edges_to_process = &(state_.edges_);
+
+  if (options->user_given_target) {
+    string err;
+    Node* user_given_target = CollectTarget(
+      options->user_given_target, &err);
+    if (!err.empty()) {
+      Error("%s: %s", options->user_given_target, err.c_str());
+      return 1;
+    }
+
+    std::vector<Edge*> user_interested_edges;
+    if (!GetAllDependentEdges(user_given_target, &user_interested_edges))
+      return 1;
+    edges_to_process = &user_interested_edges;
+  }
+
   bool first = true;
   vector<char> cwd;
 
@@ -676,8 +729,8 @@ int NinjaMain::ToolCompilationDatabase(const Options* options, int argc, char* a
   }
 
   putchar('[');
-  for (vector<Edge*>::iterator e = state_.edges_.begin();
-       e != state_.edges_.end(); ++e) {
+  for (vector<Edge*>::iterator e = edges_to_process->begin();
+       e != edges_to_process->end(); ++e) {
     if ((*e)->inputs_.empty())
       continue;
     for (int i = 0; i != argc; ++i) {
@@ -1047,9 +1100,14 @@ int ReadFlags(int* argc, char*** argv,
 
   int opt;
   while (!options->tool &&
-         (opt = getopt_long(*argc, *argv, "d:f:j:k:l:nt:vw:C:h", kLongOptions,
+         (opt = getopt_long(*argc, *argv, "a:d:f:j:k:l:nt:vw:C:h", kLongOptions,
                             NULL)) != -1) {
     switch (opt) {
+      case 'a':
+        options->user_given_target = optarg;
+        if (!options->user_given_target)
+          Fatal("Expecting one target name");
+        break;
       case 'd':
         if (!DebugEnable(optarg))
           return 1;