Reset inodes on index writes to better support hard links

src/build/adapter_filesystem.cc

@@ -68,6 +68,8 @@ auto BuildAdapterFilesystem::write_dependencies(
   this->refresh(path);
   const auto deps_path{this->dependencies_path(path)};
   std::filesystem::create_directories(deps_path.parent_path());
+  // To reset the inode and correctly handle hard links
+  std::filesystem::remove(deps_path);
   std::ofstream deps_stream{deps_path};
   assert(!deps_stream.fail());
   for (const auto &dependency : dependencies) {

src/index/generators.h

@@ -558,6 +558,8 @@ struct GENERATE_URITEMPLATE_ROUTES {
           const sourcemeta::one::BuildDynamicCallback<std::filesystem::path> &,
           const Context &router) -> void {
     std::filesystem::create_directories(destination.parent_path());
+    // To reset the inode and correctly handle hard links
+    std::filesystem::remove(destination);
     sourcemeta::core::URITemplateRouterView::save(router, destination);
   }
 };

src/index/output.h

@@ -87,6 +87,8 @@ class Output {
       -> const std::filesystem::path & {
     assert(path.is_absolute());
     std::filesystem::create_directories(path.parent_path());
+    // To reset the inode and correctly handle hard links
+    std::filesystem::remove(path);
     std::ofstream stream{path};
     assert(!stream.fail());
     sourcemeta::core::stringify(document, stream);

src/shared/metapack.cc

@@ -57,6 +57,8 @@ auto write_stream(const std::filesystem::path &path,
     metadata.assign("extension", extension);
   }
 
+  // To reset the inode and correctly handle hard links
+  std::filesystem::remove(path);
   std::ofstream output{path};
   assert(!output.fail());
   sourcemeta::core::stringify(metadata, output);

test/cli/CMakeLists.txt

@@ -58,6 +58,7 @@ if(ONE_INDEX)
   sourcemeta_one_test_cli(common index non-existent-collection-directory)
   sourcemeta_one_test_cli(common index collection-path-is-file)
   sourcemeta_one_test_cli(common index deps-contents)
+  sourcemeta_one_test_cli(common index inode-reset-on-rebuild)
 
   if(ONE_ENTERPRISE)
     sourcemeta_one_test_cli(enterprise index no-options)

test/cli/index/common/inode-reset-on-rebuild.sh

@@ -0,0 +1,86 @@
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+
+TMP="$(mktemp -d)"
+clean() { rm -rf "$TMP"; }
+trap clean EXIT
+
+cat << EOF > "$TMP/one.json"
+{
+  "url": "https://sourcemeta1.com/",
+  "contents": {
+    "schemas": {
+      "baseUri": "https://example.com/",
+      "path": "./schemas"
+    }
+  }
+}
+EOF
+
+mkdir "$TMP/schemas"
+
+cat << 'EOF' > "$TMP/schemas/test.json"
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://example.com/test"
+}
+EOF
+
+collect_inodes() {
+  find "$1" -type f -exec ls -i {} \; \
+    | awk '{print $2, $1}' | sort > "$2"
+  # Confirm the file is not empty
+  test "$(wc -l < "$2" | tr -d ' ')" -gt 0
+  # For debugging
+  cat "$2" 1>&2
+}
+
+"$1" "$TMP/one.json" "$TMP/output"
+collect_inodes "$TMP/output" "$TMP/inodes_before.txt"
+
+# Pin the original inodes by hard-linking every file into a mirror
+# directory. This prevents the filesystem from reusing freed inode
+# numbers when the indexer removes and recreates files.
+cd "$TMP/output"
+find . -type d | while read -r directory
+do
+  mkdir -p "$TMP/mirror/$directory"
+done
+find . -type f | while read -r file
+do
+  ln "$file" "$TMP/mirror/$file"
+done
+cd -
+
+# Change the registry URL and modify the schema to force all targets to rebuild
+cat << EOF > "$TMP/one.json"
+{
+  "url": "https://sourcemeta2.com/",
+  "contents": {
+    "schemas": {
+      "baseUri": "https://example.com/",
+      "path": "./schemas"
+    }
+  }
+}
+EOF
+
+cat << 'EOF' > "$TMP/schemas/test.json"
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "https://example.com/test",
+  "type": "string"
+}
+EOF
+
+"$1" "$TMP/one.json" "$TMP/output"
+collect_inodes "$TMP/output" "$TMP/inodes_after.txt"
+
+# Exactly 1 shared inode is expected: the version mark. All other files
+# must have been removed and recreated with fresh inodes.
+SHARED="$(grep --fixed-strings --line-regexp \
+  --file="$TMP/inodes_before.txt" "$TMP/inodes_after.txt" || true)"
+test "$(echo "$SHARED" | wc -l | tr -d ' ')" = "1"
+echo "$SHARED" | grep --quiet "version.json"