Print the JSON module graph correctly.

Before, we piggybacked on the implementation of regular soong_build and
wrote a fake build.ninja file to satisfy Ninja.

Now, instead, the JSON module graph is a a separate action in the Ninja
output file. This has the pleasant side effect that one can flip back
and forth between generating the JSON file and regular Soong without
loss of incrementality.

Side cleanup: write .d files in a slightly cleaner way.

Test: Presubmits.
Change-Id: Ia853383567b9dd31c53f3bdf56cfc8d517b498ec

tests/bootstrap_test.sh

@@ -607,12 +607,36 @@ EOF
 
 function test_dump_json_module_graph() {
   setup
-  SOONG_DUMP_JSON_MODULE_GRAPH="$MOCK_TOP/modules.json" run_soong
-  if [[ ! -r "$MOCK_TOP/modules.json" ]]; then
+  GENERATE_JSON_MODULE_GRAPH=1 run_soong
+  if [[ ! -r "out/soong//module-graph.json" ]]; then
     fail "JSON file was not created"
   fi
 }
 
+function test_json_module_graph_back_and_forth_null_build() {
+  setup
+
+  run_soong
+  local ninja_mtime1=$(stat -c "%y" out/soong/build.ninja)
+
+  GENERATE_JSON_MODULE_GRAPH=1 run_soong
+  local json_mtime1=$(stat -c "%y" out/soong/module-graph.json)
+
+  run_soong
+  local ninja_mtime2=$(stat -c "%y" out/soong/build.ninja)
+  if [[ "$ninja_mtime1" != "$ninja_mtime2" ]]; then
+    fail "Output Ninja file changed after writing JSON module graph"
+  fi
+
+  GENERATE_JSON_MODULE_GRAPH=1 run_soong
+  local json_mtime2=$(stat -c "%y" out/soong/module-graph.json)
+  if [[ "$json_mtime1" != "$json_mtime2" ]]; then
+    fail "JSON module graph file changed after writing Ninja file"
+  fi
+
+}
+
+
 function test_bp2build_bazel_workspace_structure {
   setup
 
@@ -757,6 +781,7 @@ test_add_file_to_soong_build
 test_glob_during_bootstrapping
 test_soong_build_rerun_iff_environment_changes
 test_dump_json_module_graph
+test_json_module_graph_back_and_forth_null_build
 test_write_to_source_tree
 test_bp2build_smoke
 test_bp2build_generates_marker_file