3 files changed, 64 insertions, 4 deletions

diff --git a/src/other_tools/repo_map/repos_to_setup_map.cpp b/src/other_tools/repo_map/repos_to_setup_map.cpp
index a65a6c50..d0396a0c 100644
--- a/src/other_tools/repo_map/repos_to_setup_map.cpp
+++ b/src/other_tools/repo_map/repos_to_setup_map.cpp
@@ -92,6 +92,29 @@ void GitCheckout(ExpressionPtr const& repo_desc,
                                             ? repo_desc_subdir->String()
                                             : "")
                       .lexically_normal();
+    // check optional mirrors
+    auto repo_desc_mirrors = repo_desc->Get("mirrors", Expression::list_t{});
+    std::vector<std::string> mirrors{};
+    if (repo_desc_mirrors->IsList()) {
+        mirrors.reserve(repo_desc_mirrors->List().size());
+        for (auto const& elem : repo_desc_mirrors->List()) {
+            if (not elem->IsString()) {
+                (*logger)(fmt::format("GitCheckout: Unsupported list entry {} "
+                                      "in optional field \"mirrors\"",
+                                      elem->ToString()),
+                          /*fatal=*/true);
+                return;
+            }
+            mirrors.emplace_back(elem->String());
+        }
+    }
+    else {
+        (*logger)(fmt::format("GitCheckout: Optional field \"mirrors\" should "
+                              "be a list of strings, but found: {}",
+                              repo_desc_mirrors->ToString()),
+                  /*fatal=*/true);
+        return;
+    }
     // check "special" pragma
     auto repo_desc_pragma = repo_desc->At("pragma");
     auto pragma_special = repo_desc_pragma
@@ -115,6 +138,7 @@ void GitCheckout(ExpressionPtr const& repo_desc,
         .repo_url = repo_desc_repository->get()->String(),
         .branch = repo_desc_branch->get()->String(),
         .subdir = subdir.empty() ? "." : subdir.string(),
+        .mirrors = std::move(mirrors),
         .origin = repo_name,
         .ignore_special = pragma_special_value == PragmaSpecial::Ignore,
         .absent = pragma_absent_value};
diff --git a/src/other_tools/root_maps/commit_git_map.cpp b/src/other_tools/root_maps/commit_git_map.cpp
index 40399811..6959dfe6 100644
--- a/src/other_tools/root_maps/commit_git_map.cpp
+++ b/src/other_tools/root_maps/commit_git_map.cpp
@@ -355,18 +355,52 @@ void EnsureCommit(GitRepoInfo const& repo_info,
                       /*fatal=*/true);
             return;
         }
-        // setup wrapped logger
+        // store failed attempts for subsequent logging
+        std::string err_messages{};
         auto wrapped_logger = std::make_shared<AsyncMapConsumerLogger>(
-            [logger](auto const& msg, bool fatal) {
-                (*logger)(fmt::format("While fetching via tmp repo:\n{}", msg),
-                          fatal);
+            [fetch_repo, &err_messages](auto const& msg, bool /*fatal*/) {
+                err_messages +=
+                    fmt::format("\nWhile attempting fetch from remote {}:\n{}",
+                                fetch_repo,
+                                msg);
             });
+        // try the main fetch URL
+        bool fetched{false};
         if (not git_repo->FetchViaTmpRepo(tmp_dir->GetPath(),
                                           fetch_repo,
                                           repo_info.branch,
                                           git_bin,
                                           launcher,
                                           wrapped_logger)) {
+            // try to fetch from mirrors, in order, if given
+            for (auto mirror : repo_info.mirrors) {
+                if (GitURLIsPath(mirror)) {
+                    mirror = std::filesystem::absolute(mirror).string();
+                }
+                wrapped_logger = std::make_shared<AsyncMapConsumerLogger>(
+                    [mirror, &err_messages](auto const& msg, bool /*fatal*/) {
+                        err_messages += fmt::format(
+                            "\nWhile attempting fetch from mirror {}:\n{}",
+                            mirror,
+                            msg);
+                    });
+                if (git_repo->FetchViaTmpRepo(tmp_dir->GetPath(),
+                                              mirror,
+                                              repo_info.branch,
+                                              git_bin,
+                                              launcher,
+                                              wrapped_logger)) {
+                    fetched = true;
+                    break;
+                }
+            }
+        }
+        if (not fetched) {
+            // log fetch failure details separately to reduce verbosity
+            (*logger)(
+                fmt::format("While fetching via tmp repo:{}", err_messages),
+                /*fatal=*/false);
+            (*logger)("Failed to fetch from provided remotes", /*fatal=*/true);
             return;
         }
         // setup wrapped logger
diff --git a/src/other_tools/root_maps/commit_git_map.hpp b/src/other_tools/root_maps/commit_git_map.hpp
index 26ed018b..a85f04e1 100644
--- a/src/other_tools/root_maps/commit_git_map.hpp
+++ b/src/other_tools/root_maps/commit_git_map.hpp
@@ -17,6 +17,7 @@
 
 #include <string>
 #include <utility>
+#include <vector>
 
 #include "nlohmann/json.hpp"
 #include "src/buildtool/common/user_structs.hpp"
@@ -32,6 +33,7 @@ struct GitRepoInfo {
     std::string repo_url{};
     std::string branch{};
     std::string subdir{}; /* key */
+    std::vector<std::string> mirrors{};
     // name of repository for which work is done; used in progress reporting
     std::string origin{};
     // create root that ignores symlinks