diff --git a/src/gn/rust_project_writer.cc b/src/gn/rust_project_writer.cc
index f78ca2d..1dc9f7a 100644
--- a/src/gn/rust_project_writer.cc
+++ b/src/gn/rust_project_writer.cc
@@ -28,7 +28,9 @@
 // Current structure of rust-project.json output file
 //
 // {
-//    "roots": [] // always empty for GN. To be deprecated.
+//    "roots": [
+//      "some/source/root"  // each crate's source root
+//    ],
 //    "crates": [
 //        {
 //            "deps": [
@@ -75,16 +77,16 @@
 
 // Map of Targets to their index in the crates list (for linking dependencies to
 // their indexes).
-using TargetIdxMap = std::unordered_map<const Target*, uint32_t>;
+using TargetIndexMap = std::unordered_map<const Target*, uint32_t>;
 
 // A collection of Targets.
-using TargetsVec = UniqueVector<const Target*>;
+using TargetsVector = UniqueVector<const Target*>;
 
 // Get the Rust deps for a target, recursively expanding OutputType::GROUPS
 // that are present in the GN structure.  This will return a flattened list of
 // deps from the groups, but will not expand a Rust lib dependency to find any
 // transitive Rust dependencies.
-void GetRustDeps(const Target* target, TargetsVec* rust_deps) {
+void GetRustDeps(const Target* target, TargetsVector* rust_deps) {
   for (const auto& pair : target->GetDeps(Target::DEPS_LINKED)) {
     const Target* dep = pair.ptr;
 
@@ -97,52 +99,12 @@
     }
   }
 }
-TargetsVec GetRustDeps(const Target* target) {
-  TargetsVec deps;
+TargetsVector GetRustDeps(const Target* target) {
+  TargetsVector deps;
   GetRustDeps(target, &deps);
   return deps;
 }
 
-void WriteDeps(const Target* target,
-               TargetIdxMap& lookup,
-               SysrootIdxMap& sysroot_lookup,
-               std::ostream& rust_project) {
-  bool first_dep = true;
-
-  rust_project << "      \"deps\": [";
-
-  // Check if this target has had it's sysroot setup yet
-  auto rust_tool =
-      target->toolchain()->GetToolForSourceTypeAsRust(SourceFile::SOURCE_RS);
-  auto current_sysroot = rust_tool->GetSysroot();
-  if (current_sysroot != "") {
-    // TODO(bwb) If this library doesn't depend on std, use core instead
-    auto std_idx = sysroot_lookup[current_sysroot].find("std");
-    if (std_idx != sysroot_lookup[current_sysroot].end()) {
-      if (!first_dep)
-        rust_project << ",";
-      rust_project << NEWLINE << "        {" NEWLINE
-                   << "          \"crate\": " << std::to_string(std_idx->second)
-                   << "," NEWLINE << "          \"name\": \"std\"" NEWLINE
-                   << "        }";
-      first_dep = false;
-    }
-  }
-
-  for (const auto& dep : GetRustDeps(target)) {
-    auto idx = lookup[dep];
-    if (!first_dep)
-      rust_project << ",";
-    rust_project << NEWLINE << "        {" NEWLINE
-                 << "          \"crate\": " << std::to_string(idx)
-                 << "," NEWLINE << "          \"name\": \""
-                 << dep->rust_values().crate_name() << "\"" NEWLINE
-                 << "        }";
-    first_dep = false;
-  }
-  rust_project << NEWLINE "      ]," NEWLINE;
-}
-
 // TODO(bwb) Parse sysroot structure from toml files. This is fragile and might
 // break if upstream changes the dependency structure.
 const std::string_view sysroot_crates[] = {"std",
@@ -159,7 +121,6 @@
                                            "alloc_system",
                                            "compiler_builtins",
                                            "getopts",
-                                           "panic_unwind",
                                            "panic_abort",
                                            "unwind",
                                            "build_helper",
@@ -176,13 +137,11 @@
                         {"std", {"alloc", "core", "panic_abort", "unwind"}}};
 
 // Add each of the crates a sysroot has, including their dependencies.
-void AddSysrootCrate(const std::string_view crate,
+void AddSysrootCrate(const BuildSettings* build_settings,
+                     const std::string_view crate,
                      const std::string_view current_sysroot,
-                     uint32_t* count,
-                     SysrootCrateIdxMap& sysroot_crate_lookup,
-                     std::ostream& rust_project,
-                     const BuildSettings* build_settings,
-                     bool first_crate) {
+                     SysrootCrateIndexMap& sysroot_crate_lookup,
+                     CrateList& crate_list) {
   if (sysroot_crate_lookup.find(crate) != sysroot_crate_lookup.end()) {
     // If this sysroot crate is already in the lookup, we don't add it again.
     return;
@@ -193,60 +152,39 @@
   if (deps_lookup != sysroot_deps_map.end()) {
     auto deps = (*deps_lookup).second;
     for (auto dep : deps) {
-      AddSysrootCrate(dep, current_sysroot, count, sysroot_crate_lookup,
-                      rust_project, build_settings, first_crate);
-      first_crate = false;
+      AddSysrootCrate(build_settings, dep, current_sysroot,
+                      sysroot_crate_lookup, crate_list);
     }
   }
 
-  if (!first_crate)
-    rust_project << "," NEWLINE;
-  first_crate = false;
-  sysroot_crate_lookup.insert(std::make_pair(crate, *count));
+  size_t crate_index = crate_list.size();
+  sysroot_crate_lookup.insert(std::make_pair(crate, crate_index));
 
   base::FilePath rebased_out_dir =
       build_settings->GetFullPath(build_settings->build_dir());
   auto crate_path =
       FilePathToUTF8(rebased_out_dir) + std::string(current_sysroot) +
       "/lib/rustlib/src/rust/src/lib" + std::string(crate) + "/lib.rs";
-  base::FilePath crate_root = build_settings->GetFullPath(crate_path, false);
 
-  rust_project << "    {" NEWLINE;
-  rust_project << "      \"crate_id\": " << std::to_string(*count)
-               << "," NEWLINE;
-  rust_project << "      \"root_module\": \"" << FilePathToUTF8(crate_root)
-               << "\"," NEWLINE;
-  rust_project << "      \"edition\": \"2018\"," NEWLINE;
-  rust_project << "      \"deps\": [";
-  (*count)++;
+  Crate sysroot_crate =
+      Crate(SourceFile(crate_path), crate_index, std::string(crate), "2018");
+
   if (deps_lookup != sysroot_deps_map.end()) {
     auto deps = (*deps_lookup).second;
-    bool first_dep = true;
     for (auto dep : deps) {
       auto idx = sysroot_crate_lookup[dep];
-      if (!first_dep)
-        rust_project << ",";
-      first_dep = false;
-      rust_project << NEWLINE "        {" NEWLINE
-                   << "          \"crate\": " << std::to_string(idx)
-                   << "," NEWLINE "          \"name\": \"" << dep
-                   << "\"" NEWLINE "        }";
+      sysroot_crate.AddDependency(idx, std::string(dep));
     }
   }
-  rust_project << NEWLINE "      ]," NEWLINE;
 
-  rust_project << "      \"cfg\": []" NEWLINE;
-
-  rust_project << "    }";
+  crate_list.push_back(sysroot_crate);
 }
 
 // Add the given sysroot to the project, if it hasn't already been added.
-void AddSysroot(const std::string_view sysroot,
-                uint32_t* count,
-                SysrootIdxMap& sysroot_lookup,
-                std::ostream& rust_project,
-                const BuildSettings* build_settings,
-                bool first_crate) {
+void AddSysroot(const BuildSettings* build_settings,
+                const std::string_view sysroot,
+                SysrootIndexMap& sysroot_lookup,
+                CrateList& crate_list) {
   // If this sysroot is already in the lookup, we don't add it again.
   if (sysroot_lookup.find(sysroot) != sysroot_lookup.end()) {
     return;
@@ -254,74 +192,57 @@
 
   // Otherwise, add all of its crates
   for (auto crate : sysroot_crates) {
-    AddSysrootCrate(crate, sysroot, count, sysroot_lookup[sysroot],
-                    rust_project, build_settings, first_crate);
-    first_crate = false;
+    AddSysrootCrate(build_settings, crate, sysroot, sysroot_lookup[sysroot],
+                    crate_list);
   }
 }
 
-void AddTarget(const Target* target,
-               uint32_t* count,
-               TargetIdxMap& lookup,
-               SysrootIdxMap& sysroot_lookup,
-               const BuildSettings* build_settings,
-               std::ostream& rust_project,
-               bool first_crate) {
+void AddTarget(const BuildSettings* build_settings,
+               const Target* target,
+               TargetIndexMap& lookup,
+               SysrootIndexMap& sysroot_lookup,
+               CrateList& crate_list) {
   if (lookup.find(target) != lookup.end()) {
     // If target is already in the lookup, we don't add it again.
     return;
   }
 
-  // Check what sysroot this target needs.
+  // Check what sysroot this target needs.  Add it to the crate list if it
+  // hasn't already been added.
   auto rust_tool =
       target->toolchain()->GetToolForSourceTypeAsRust(SourceFile::SOURCE_RS);
   auto current_sysroot = rust_tool->GetSysroot();
   if (current_sysroot != "" && sysroot_lookup.count(current_sysroot) == 0) {
-    AddSysroot(current_sysroot, count, sysroot_lookup, rust_project,
-               build_settings, first_crate);
-    first_crate = false;
+    AddSysroot(build_settings, current_sysroot, sysroot_lookup, crate_list);
   }
 
-  for (const auto& dep : GetRustDeps(target)) {
-    AddTarget(dep, count, lookup, sysroot_lookup, build_settings, rust_project,
-              first_crate);
-    first_crate = false;
+  auto crate_deps = GetRustDeps(target);
+
+  // Add all dependencies of this crate, before this crate.
+  for (const auto& dep : crate_deps) {
+    AddTarget(build_settings, dep, lookup, sysroot_lookup, crate_list);
   }
 
-  if (!first_crate)
-    rust_project << "," NEWLINE;
-
-  // Construct the crate info.
-  rust_project << "    {" NEWLINE;
-  rust_project << "      \"crate_id\": " << std::to_string(*count)
-               << "," NEWLINE;
+  // The index of a crate is its position (0-based) in the list of crates.
+  size_t crate_id = crate_list.size();
 
   // Add the target to the crate lookup.
-  lookup.insert(std::make_pair(target, *count));
-  (*count)++;
+  lookup.insert(std::make_pair(target, crate_id));
 
-  base::FilePath crate_root =
-      build_settings->GetFullPath(target->rust_values().crate_root());
-
-  rust_project << "      \"root_module\": \"" << FilePathToUTF8(crate_root)
-               << "\"," NEWLINE;
-  rust_project << "      \"label\": \""
-               << target->label().GetUserVisibleName(false) << "\"," NEWLINE;
-
-  WriteDeps(target, lookup, sysroot_lookup, rust_project);
+  SourceFile crate_root = target->rust_values().crate_root();
+  std::string crate_label = target->label().GetUserVisibleName(false);
 
   std::string cfg_prefix("--cfg=");
   std::string edition_prefix("--edition=");
-  std::vector<std::string> cfgs;
+  ConfigList cfgs;
 
-  bool edition_set = false;
+  std::string edition = "2015";  // default to be overridden as needed
+
   for (ConfigValuesIterator iter(target); !iter.done(); iter.Next()) {
     for (const auto& flag : iter.cur().rustflags()) {
       // extract the edition of this target
       if (!flag.compare(0, edition_prefix.size(), edition_prefix)) {
-        auto edition = flag.substr(edition_prefix.size());
-        rust_project << "      \"edition\": \"" << edition << "\"," NEWLINE;
-        edition_set = true;
+        edition = flag.substr(edition_prefix.size());
       }
       if (!flag.compare(0, cfg_prefix.size(), cfg_prefix)) {
         auto cfg = flag.substr(cfg_prefix.size());
@@ -332,47 +253,109 @@
     }
   }
 
-  if (!edition_set)
-    rust_project << "      \"edition\": \"2015\"," NEWLINE;
+  Crate crate = Crate(crate_root, crate_id, crate_label, edition);
 
-  rust_project << "      \"cfg\": [";
-  bool first_cfg = true;
-  for (const auto& cfg : cfgs) {
-    if (!first_cfg)
-      rust_project << ",";
-    first_cfg = false;
-    rust_project << NEWLINE;
-    rust_project << "        \"" << cfg << "\"";
+  for (auto& cfg : cfgs) {
+    crate.AddConfigItem(cfg);
   }
-  rust_project << NEWLINE;
-  rust_project << "      ]" NEWLINE;
 
-  rust_project << "    }";
+  // Add the sysroot dependency, if there is one.
+  if (current_sysroot != "") {
+    // TODO(bwb) If this library doesn't depend on std, use core instead
+    auto std_idx = sysroot_lookup[current_sysroot].find("std");
+    if (std_idx != sysroot_lookup[current_sysroot].end()) {
+      crate.AddDependency(std_idx->second, "std");
+    }
+  }
+
+  // Add the rest of the crate dependencies.
+  for (const auto& dep : crate_deps) {
+    auto idx = lookup[dep];
+    crate.AddDependency(idx, dep->rust_values().crate_name());
+  }
+
+  crate_list.push_back(crate);
+}
+
+void WriteCrates(const BuildSettings* build_settings,
+                 CrateList& crate_list,
+                 std::ostream& rust_project) {
+  rust_project << "{" NEWLINE;
+  rust_project << "  \"roots\": [";
+  bool first_root = true;
+  for (auto& crate : crate_list) {
+    if (!first_root)
+      rust_project << ",";
+    first_root = false;
+
+    std::string root_dir =
+        FilePathToUTF8(build_settings->GetFullPath(crate.root().GetDir()));
+    rust_project << NEWLINE "    \"" << root_dir << "\"";
+  }
+  rust_project << NEWLINE "  ]," NEWLINE;
+  rust_project << "  \"crates\": [";
+  bool first_crate = true;
+  for (auto& crate : crate_list) {
+    if (!first_crate)
+      rust_project << ",";
+    first_crate = false;
+
+    auto crate_root = FilePathToUTF8(build_settings->GetFullPath(crate.root()));
+
+    rust_project << NEWLINE << "    {" NEWLINE
+                 << "      \"crate_id\": " << crate.index() << "," NEWLINE
+                 << "      \"root_module\": \"" << crate_root << "\"," NEWLINE
+                 << "      \"label\": \"" << crate.label() << "\"," NEWLINE
+                 << "      \"deps\": [";
+
+    bool first_dep = true;
+    for (auto& dep : crate.dependencies()) {
+      if (!first_dep)
+        rust_project << ",";
+      first_dep = false;
+
+      rust_project << NEWLINE << "        {" NEWLINE
+                   << "          \"crate\": " << dep.first << "," NEWLINE
+                   << "          \"name\": \"" << dep.second << "\"" NEWLINE
+                   << "        }";
+    }
+    rust_project << NEWLINE "      ]," NEWLINE;  // end dep list
+
+    rust_project << "      \"edition\": \"" << crate.edition() << "\"," NEWLINE;
+
+    rust_project << "      \"cfg\": [";
+    bool first_cfg = true;
+    for (const auto& cfg : crate.configs()) {
+      if (!first_cfg)
+        rust_project << ",";
+      first_cfg = false;
+
+      rust_project << NEWLINE;
+      rust_project << "        \"" << cfg << "\"";
+    }
+    rust_project << NEWLINE;
+    rust_project << "      ]" NEWLINE;  // end cfgs
+
+    rust_project << "    }";  // end crate
+  }
+  rust_project << NEWLINE "  ]" NEWLINE;  // end crate list
+  rust_project << "}" NEWLINE;
 }
 
 void RustProjectWriter::RenderJSON(const BuildSettings* build_settings,
                                    std::vector<const Target*>& all_targets,
                                    std::ostream& rust_project) {
-  TargetIdxMap lookup;
-  SysrootIdxMap sysroot_lookup;
-  uint32_t count = 0;
-  bool first = true;
-
-  rust_project << "{" NEWLINE;
-
-  rust_project << "  \"roots\": []," NEWLINE;
-  rust_project << "  \"crates\": [" NEWLINE;
+  TargetIndexMap lookup;
+  SysrootIndexMap sysroot_lookup;
+  CrateList crate_list;
 
   // All the crates defined in the project.
   for (const auto* target : all_targets) {
     if (!target->IsBinary() || !target->source_types_used().RustSourceUsed())
       continue;
 
-    AddTarget(target, &count, lookup, sysroot_lookup, build_settings,
-              rust_project, first);
-    first = false;
+    AddTarget(build_settings, target, lookup, sysroot_lookup, crate_list);
   }
 
-  rust_project << NEWLINE "  ]" NEWLINE;
-  rust_project << "}" NEWLINE;
+  WriteCrates(build_settings, crate_list, rust_project);
 }
diff --git a/src/gn/rust_project_writer_helpers.h b/src/gn/rust_project_writer_helpers.h
index a70b280..25340b3 100644
--- a/src/gn/rust_project_writer_helpers.h
+++ b/src/gn/rust_project_writer_helpers.h
@@ -7,37 +7,94 @@
 
 #include <fstream>
 #include <sstream>
+#include <string>
+#include <tuple>
 #include <unordered_map>
+#include <vector>
 
 #include "build_settings.h"
+#include "gn/source_file.h"
 #include "gn/target.h"
 
 // These are internal types and helper functions for RustProjectWriter that have
 // been extracted for easier testability.
 
+// Crate Index in the generated file
+using CrateIndex = size_t;
+
+using ConfigList = std::vector<std::string>;
+using Dependency = std::pair<CrateIndex, std::string>;
+using DependencyList = std::vector<Dependency>;
+
+// This class represents a crate to be serialized out as part of the
+// rust-project.json file.  This is used to separate the generating
+// of the data that needs to be in the file, from the file itself.
+class Crate {
+ public:
+  Crate(SourceFile root,
+        CrateIndex index,
+        std::string label,
+        std::string edition)
+      : root_(root), index_(index), label_(label), edition_(edition) {}
+
+  ~Crate() = default;
+
+  // Add a config item to the crate.
+  void AddConfigItem(std::string cfg_item) { configs_.push_back(cfg_item); }
+
+  // Add another crate as a dependency of this one.
+  void AddDependency(CrateIndex index, std::string name) {
+    deps_.push_back(std::make_pair(index, name));
+  }
+
+  // Returns the root file for the crate.
+  SourceFile& root() { return root_; }
+
+  // Returns the crate index.
+  CrateIndex index() { return index_; };
+
+  // Returns the displayable crate label.
+  const std::string& label() { return label_; }
+
+  // Returns the Rust Edition this crate uses.
+  const std::string& edition() { return edition_; }
+
+  // Return the set of config items for this crate.
+  ConfigList& configs() { return configs_; }
+
+  // Return the set of dependencies for this crate.
+  DependencyList& dependencies() { return deps_; }
+
+ private:
+  SourceFile root_;
+  CrateIndex index_;
+  std::string label_;
+  std::string edition_;
+  ConfigList configs_;
+  DependencyList deps_;
+};
+
+using CrateList = std::vector<Crate>;
+
 // Mapping of a sysroot crate (path) to it's index in the crates list.
-using SysrootCrateIdxMap = std::unordered_map<std::string_view, uint32_t>;
+using SysrootCrateIndexMap = std::unordered_map<std::string_view, CrateIndex>;
 
 // Mapping of a sysroot (path) to the mapping of each of the sysroot crates to
 // their index in the crates list.
-using SysrootIdxMap = std::unordered_map<std::string_view, SysrootCrateIdxMap>;
+using SysrootIndexMap =
+    std::unordered_map<std::string_view, SysrootCrateIndexMap>;
 
 // Add all of the crates for a sysroot (path) to the rust_project ostream.
-void AddSysroot(const std::string_view sysroot,
-                uint32_t* count,
-                SysrootIdxMap& sysroot_lookup,
-                std::ostream& rust_project,
-                const BuildSettings* build_settings,
-                bool first_crate);
+// Add the given sysroot to the project, if it hasn't already been added.
+void AddSysroot(const BuildSettings* build_settings,
+                const std::string_view sysroot,
+                SysrootIndexMap& sysroot_lookup,
+                CrateList& crate_list);
 
-// Add a sysroot crate to the rust_project ostream, first recursively adding its
-// sysroot crate depedencies.
-void AddSysrootCrate(const std::string_view crate,
-                     const std::string_view current_sysroot,
-                     uint32_t* count,
-                     SysrootCrateIdxMap& sysroot_crate_lookup,
-                     std::ostream& rust_project,
-                     const BuildSettings* build_settings,
-                     bool first_crate);
+// Write the entire rust-project.json file contents into the given stream, based
+// on the the given crates list.
+void WriteCrates(const BuildSettings* build_settings,
+                 CrateList& crate_list,
+                 std::ostream& rust_project);
 
-#endif  // TOOLS_GN_RUST_PROJECT_WRITER_HELPERS_H_
\ No newline at end of file
+#endif  // TOOLS_GN_RUST_PROJECT_WRITER_HELPERS_H_
diff --git a/src/gn/rust_project_writer_helpers_unittest.cc b/src/gn/rust_project_writer_helpers_unittest.cc
index bb932ad..19501c4 100644
--- a/src/gn/rust_project_writer_helpers_unittest.cc
+++ b/src/gn/rust_project_writer_helpers_unittest.cc
@@ -5,6 +5,7 @@
 #include "gn/rust_project_writer_helpers.h"
 
 #include "base/strings/string_util.h"
+#include "gn/filesystem_utils.h"
 #include "gn/string_output_buffer.h"
 #include "gn/test_with_scheduler.h"
 #include "gn/test_with_scope.h"
@@ -13,219 +14,349 @@
 
 using RustProjectWriterHelper = TestWithScheduler;
 
-TEST_F(RustProjectWriterHelper, SysrootDepsAreCorrect) {
+TEST_F(RustProjectWriterHelper, WriteCrates) {
   TestWithScope setup;
 
-  SysrootIdxMap sysroot_lookup;
-  uint32_t current_crate_count = 2;
+  CrateList crates;
+  Crate dep = Crate(SourceFile("/root/tortoise/lib.rs"), 0, "//tortoise:bar", "2015");
+  Crate target = Crate(SourceFile("/root/hare/lib.rs"), 1, "//hare:bar", "2015");
+  target.AddDependency(0, "tortoise");
+  target.AddConfigItem("unix");
+  target.AddConfigItem("feature=\\\"test\\\"");
+
+  crates.push_back(dep);
+  crates.push_back(target);
 
   std::ostringstream stream;
+  WriteCrates(setup.build_settings(), crates, stream);
+  std::string out = stream.str();
+#if defined(OS_WIN)
+  base::ReplaceSubstringsAfterOffset(&out, 0, "\r\n", "\n");
+#endif
+  const char expected_json[] =
+      "{\n"
+      "  \"roots\": [\n"
+      "    \"/root/tortoise/\",\n"
+      "    \"/root/hare/\"\n"
+      "  ],\n"
+      "  \"crates\": [\n"
+      "    {\n"
+      "      \"crate_id\": 0,\n"
+      "      \"root_module\": \"/root/tortoise/lib.rs\",\n"
+      "      \"label\": \"//tortoise:bar\",\n"
+      "      \"deps\": [\n"
+      "      ],\n"
+      "      \"edition\": \"2015\",\n"
+      "      \"cfg\": [\n"
+      "      ]\n"
+      "    },\n"
+      "    {\n"
+      "      \"crate_id\": 1,\n"
+      "      \"root_module\": \"/root/hare/lib.rs\",\n"
+      "      \"label\": \"//hare:bar\",\n"
+      "      \"deps\": [\n"
+      "        {\n"
+      "          \"crate\": 0,\n"
+      "          \"name\": \"tortoise\"\n"
+      "        }\n"
+      "      ],\n"
+      "      \"edition\": \"2015\",\n"
+      "      \"cfg\": [\n"
+      "        \"unix\",\n"
+      "        \"feature=\\\"test\\\"\"\n"
+      "      ]\n"
+      "    }\n"
+      "  ]\n"
+      "}\n";
 
-  AddSysroot("path", &current_crate_count, sysroot_lookup, stream, setup.build_settings(),
-             false);
+  EXPECT_EQ(expected_json, out);
+}
 
+TEST_F(RustProjectWriterHelper, SysrootDepsAreCorrect) {
+  TestWithScope setup;
+  setup.build_settings()->SetRootPath(UTF8ToFilePath("/root"));
+
+  SysrootIndexMap sysroot_lookup;
+  CrateList crates;
+
+  AddSysroot(setup.build_settings(), "sysroot", sysroot_lookup, crates);
+
+  std::ostringstream stream;
+  WriteCrates(setup.build_settings(), crates, stream);
   std::string out = stream.str();
 #if defined(OS_WIN)
   base::ReplaceSubstringsAfterOffset(&out, 0, "\r\n", "\n");
 #endif
 
-const char expected_json[] = ",\n"
+const char expected_json[] =
+    "{\n"
+    "  \"roots\": [\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libcore/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liballoc/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libpanic_abort/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libunwind/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libstd/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libcollections/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liblibc/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libpanic_unwind/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libproc_macro/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_unicode/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libstd_unicode/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libtest/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liballoc_jemalloc/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liballoc_system/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libcompiler_builtins/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libgetopts/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libbuild_helper/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_asan/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_lsan/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_msan/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_tsan/\",\n"
+    "    \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libsyntax/\"\n"
+    "  ],\n"
+    "  \"crates\": [\n"
     "    {\n"
-    "      \"crate_id\": 2,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libcore/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"crate_id\": 0,\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libcore/lib.rs\",\n"
+    "      \"label\": \"core\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
+    "    },\n"
+    "    {\n"
+    "      \"crate_id\": 1,\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liballoc/lib.rs\",\n"
+    "      \"label\": \"alloc\",\n"
+    "      \"deps\": [\n"
+    "        {\n"
+    "          \"crate\": 0,\n"
+    "          \"name\": \"core\"\n"
+    "        }\n"
+    "      ],\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
+    "    },\n"
+    "    {\n"
+    "      \"crate_id\": 2,\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libpanic_abort/lib.rs\",\n"
+    "      \"label\": \"panic_abort\",\n"
+    "      \"deps\": [\n"
+    "      ],\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 3,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/liballoc/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libunwind/lib.rs\",\n"
+    "      \"label\": \"unwind\",\n"
     "      \"deps\": [\n"
-    "        {\n"
-    "          \"crate\": 2,\n"
-    "          \"name\": \"core\"\n"
-    "        }\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 4,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libpanic_abort/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
-    "      \"deps\": [\n"
-    "      ],\n"
-    "      \"cfg\": []\n"
-    "    },\n"
-    "    {\n"
-    "      \"crate_id\": 5,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libunwind/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
-    "      \"deps\": [\n"
-    "      ],\n"
-    "      \"cfg\": []\n"
-    "    },\n"
-    "    {\n"
-    "      \"crate_id\": 6,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libstd/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libstd/lib.rs\",\n"
+    "      \"label\": \"std\",\n"
     "      \"deps\": [\n"
     "        {\n"
-    "          \"crate\": 3,\n"
+    "          \"crate\": 1,\n"
     "          \"name\": \"alloc\"\n"
     "        },\n"
     "        {\n"
-    "          \"crate\": 2,\n"
+    "          \"crate\": 0,\n"
     "          \"name\": \"core\"\n"
     "        },\n"
     "        {\n"
-    "          \"crate\": 4,\n"
+    "          \"crate\": 2,\n"
     "          \"name\": \"panic_abort\"\n"
     "        },\n"
     "        {\n"
-    "          \"crate\": 5,\n"
+    "          \"crate\": 3,\n"
     "          \"name\": \"unwind\"\n"
     "        }\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
+    "    },\n"
+    "    {\n"
+    "      \"crate_id\": 5,\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libcollections/lib.rs\",\n"
+    "      \"label\": \"collections\",\n"
+    "      \"deps\": [\n"
+    "      ],\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
+    "    },\n"
+    "    {\n"
+    "      \"crate_id\": 6,\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liblibc/lib.rs\",\n"
+    "      \"label\": \"libc\",\n"
+    "      \"deps\": [\n"
+    "      ],\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 7,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libcollections/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libpanic_unwind/lib.rs\",\n"
+    "      \"label\": \"panic_unwind\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 8,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/liblibc/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libproc_macro/lib.rs\",\n"
+    "      \"label\": \"proc_macro\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 9,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libpanic_unwind/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_unicode/lib.rs\",\n"
+    "      \"label\": \"rustc_unicode\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 10,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libproc_macro/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libstd_unicode/lib.rs\",\n"
+    "      \"label\": \"std_unicode\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 11,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/librustc_unicode/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libtest/lib.rs\",\n"
+    "      \"label\": \"test\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 12,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libstd_unicode/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liballoc_jemalloc/lib.rs\",\n"
+    "      \"label\": \"alloc_jemalloc\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 13,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libtest/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/liballoc_system/lib.rs\",\n"
+    "      \"label\": \"alloc_system\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 14,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/liballoc_jemalloc/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libcompiler_builtins/lib.rs\",\n"
+    "      \"label\": \"compiler_builtins\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 15,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/liballoc_system/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libgetopts/lib.rs\",\n"
+    "      \"label\": \"getopts\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 16,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libcompiler_builtins/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libbuild_helper/lib.rs\",\n"
+    "      \"label\": \"build_helper\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 17,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libgetopts/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_asan/lib.rs\",\n"
+    "      \"label\": \"rustc_asan\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 18,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libbuild_helper/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_lsan/lib.rs\",\n"
+    "      \"label\": \"rustc_lsan\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 19,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/librustc_asan/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_msan/lib.rs\",\n"
+    "      \"label\": \"rustc_msan\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 20,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/librustc_lsan/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/librustc_tsan/lib.rs\",\n"
+    "      \"label\": \"rustc_tsan\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
+    "      \"edition\": \"2018\",\n"
+    "      \"cfg\": [\n"
+    "      ]\n"
     "    },\n"
     "    {\n"
     "      \"crate_id\": 21,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/librustc_msan/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
+    "      \"root_module\": \"/root/out/Debug/sysroot/lib/rustlib/src/rust/src/libsyntax/lib.rs\",\n"
+    "      \"label\": \"syntax\",\n"
     "      \"deps\": [\n"
     "      ],\n"
-    "      \"cfg\": []\n"
-    "    },\n"
-    "    {\n"
-    "      \"crate_id\": 22,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/librustc_tsan/lib.rs\",\n"
     "      \"edition\": \"2018\",\n"
-    "      \"deps\": [\n"
-    "      ],\n"
-    "      \"cfg\": []\n"
-    "    },\n"
-    "    {\n"
-    "      \"crate_id\": 23,\n"
-    "      \"root_module\": \"out/Debug/path/lib/rustlib/src/rust/src/libsyntax/lib.rs\",\n"
-    "      \"edition\": \"2018\",\n"
-    "      \"deps\": [\n"
-    "      ],\n"
-    "      \"cfg\": []\n"
-    "    }"
+    "      \"cfg\": [\n"
+    "      ]\n"
+    "    }\n"
+    "  ]\n"
+    "}\n";
 ;
   EXPECT_EQ(expected_json, out);
 }
diff --git a/src/gn/rust_project_writer_unittest.cc b/src/gn/rust_project_writer_unittest.cc
index fb7200e..a1910e7 100644
--- a/src/gn/rust_project_writer_unittest.cc
+++ b/src/gn/rust_project_writer_unittest.cc
@@ -4,6 +4,8 @@
 
 #include "gn/rust_project_writer.h"
 #include "base/strings/string_util.h"
+#include "base/files/file_path.h"
+#include "gn/filesystem_utils.h"
 #include "gn/substitution_list.h"
 #include "gn/target.h"
 #include "gn/test_with_scheduler.h"
@@ -16,6 +18,7 @@
 TEST_F(RustProjectJSONWriter, OneRustTarget) {
   Err err;
   TestWithScope setup;
+  setup.build_settings()->SetRootPath(UTF8ToFilePath("path"));
 
   Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
   target.set_output_type(Target::RUST_LIBRARY);
@@ -39,11 +42,13 @@
 #endif
   const char expected_json[] =
       "{\n"
-      "  \"roots\": [],\n"
+      "  \"roots\": [\n"
+      "    \"path/foo/\"\n"
+      "  ],\n"
       "  \"crates\": [\n"
       "    {\n"
       "      \"crate_id\": 0,\n"
-      "      \"root_module\": \"foo/lib.rs\",\n"
+      "      \"root_module\": \"path/foo/lib.rs\",\n"
       "      \"label\": \"//foo:bar\",\n"
       "      \"deps\": [\n"
       "      ],\n"
@@ -94,7 +99,10 @@
 #endif
   const char expected_json[] =
       "{\n"
-      "  \"roots\": [],\n"
+      "  \"roots\": [\n"
+      "    \"tortoise/\",\n"
+      "    \"hare/\"\n"
+      "  ],\n"
       "  \"crates\": [\n"
       "    {\n"
       "      \"crate_id\": 0,\n"
@@ -173,7 +181,11 @@
 #endif
   const char expected_json[] =
       "{\n"
-      "  \"roots\": [],\n"
+      "  \"roots\": [\n"
+      "    \"tortoise/\",\n"
+      "    \"achilles/\",\n"
+      "    \"hare/\"\n"
+      "  ],\n"
       "  \"crates\": [\n"
       "    {\n"
       "      \"crate_id\": 0,\n"
@@ -280,7 +292,11 @@
 #endif
   const char expected_json[] =
       "{\n"
-      "  \"roots\": [],\n"
+      "  \"roots\": [\n"
+      "    \"tortoise/\",\n"
+      "    \"tortoise/macro/\",\n"
+      "    \"hare/\"\n"
+      "  ],\n"
       "  \"crates\": [\n"
       "    {\n"
       "      \"crate_id\": 0,\n"