Make nix path-info --json return an object not array

Before it returned a list of JSON objects with store object information,
including the path in each object. Now, it maps the paths to JSON
objects with the metadata sans path.

This matches how `nix derivation show` works.

In the process of doing this, shuffle around the `ValidPathInfo` JSON
rendering logic into what I hope is a better state:

`Store::pathInfoToJSON` was a rather baroque functions, being full of
parameters to support both parsed derivations and `nix path-info`. The
common core of each, a simple `UnkeyedValidPathInfo::toJSON` function,
is factored out, but the rest of the logic is just duplicated and then
specialized to its use-case (at which point it is no longer that
duplicated).

This keeps the human oriented CLI logic (which is currently stable) and
the core domain logic (export reference graphs with structured attrs,
which is stable), separate, which I think is better.

Quite hillariously, none of our existing tests caught this change to
`path-info --json` though they did use it. So just new tests need to be
added.

doc/manual/src/release-notes/rl-next.md

@@ -15,3 +15,36 @@
 - `nix-shell` shebang lines now support single-quoted arguments.
 
 - `builtins.fetchTree` is now marked as stable.
+
+- [`nix path-info --json`](@docroot@/command-ref/new-cli/nix3-path-info.md)
+  (experimental) now returns a JSON map rather than JSON list.
+  The path field of each object has instead become the key in th outer map, since it is unique.
+
+  - Old way:
+
+    ```json
+    [
+      {
+        path = "/nix/store/8fv91097mbh5049i9rglc73dx6kjg3qk-bash-5.2-p15",
+        // ...
+      },
+        path = "/nix/store/wffw7l0alvs3iw94cbgi1gmmbmw99sqb-home-manager-path",
+        // ...
+      }
+    ]
+    ```
+
+  - New way
+
+    ```json
+    {
+      "/nix/store/8fv91097mbh5049i9rglc73dx6kjg3qk-bash-5.2-p15": {
+        // ...
+      },
+      "/nix/store/wffw7l0alvs3iw94cbgi1gmmbmw99sqb-home-manager-path": {
+        // ...
+      }
+    }
+    ```
+
+  This makes it match `nix derivation show`, which also maps store paths to information.

src/libstore/nar-info.cc

@@ -125,4 +125,25 @@ std::string NarInfo::to_string(const Store & store) const
     return res;
 }
 
+nlohmann::json NarInfo::toJSON(
+    const Store & store,
+    bool includeImpureInfo,
+    HashFormat hashFormat) const
+{
+    using nlohmann::json;
+
+    auto jsonObject = ValidPathInfo::toJSON(store, includeImpureInfo, hashFormat);
+
+    if (includeImpureInfo) {
+        if (!url.empty())
+            jsonObject["url"] = url;
+        if (fileHash)
+            jsonObject["downloadHash"] = fileHash->to_string(hashFormat, true);
+        if (fileSize)
+            jsonObject["downloadSize"] = fileSize;
+    }
+
+    return jsonObject;
+}
+
 }

src/libstore/nar-info.hh

@@ -25,6 +25,14 @@ struct NarInfo : ValidPathInfo
     NarInfo(const Store & store, const std::string & s, const std::string & whence);
 
     std::string to_string(const Store & store) const;
+
+    nlohmann::json toJSON(
+        const Store & store,
+        bool includeImpureInfo,
+        HashFormat hashFormat) const override;
+    static NarInfo fromJSON(
+        const Store & store,
+        const nlohmann::json & json);
 };
 
 }

src/libstore/parsed-derivations.cc

@@ -132,6 +132,39 @@ bool ParsedDerivation::useUidRange() const
 
 static std::regex shVarName("[A-Za-z_][A-Za-z0-9_]*");
 
+/**
+ * Write a JSON representation of store object metadata, such as the
+ * hash and the references.
+ */
+static nlohmann::json pathInfoToJSON(
+    Store & store,
+    const StorePathSet & storePaths)
+{
+    nlohmann::json::array_t jsonList = nlohmann::json::array();
+
+    for (auto & storePath : storePaths) {
+        auto info = store.queryPathInfo(storePath);
+
+        auto & jsonPath = jsonList.emplace_back(
+            info->toJSON(store, false, HashFormat::Base32));
+
+        // Add the path to the object whose metadata we are including.
+        jsonPath["path"] = store.printStorePath(storePath);
+
+        jsonPath["closureSize"] = ({
+            uint64_t totalNarSize = 0;
+            StorePathSet closure;
+            store.computeFSClosure(info->path, closure, false, false);
+            for (auto & p : closure) {
+                auto info = store.queryPathInfo(p);
+                totalNarSize += info->narSize;
+            }
+            totalNarSize;
+        });
+    }
+    return jsonList;
+}
+
 std::optional<nlohmann::json> ParsedDerivation::prepareStructuredAttrs(Store & store, const StorePathSet & inputPaths)
 {
     auto structuredAttrs = getStructuredAttrs();
@@ -152,8 +185,8 @@ std::optional<nlohmann::json> ParsedDerivation::prepareStructuredAttrs(Store & s
             StorePathSet storePaths;
             for (auto & p : *i)
                 storePaths.insert(store.parseStorePath(p.get<std::string>()));
-            json[i.key()] = store.pathInfoToJSON(
-                store.exportReferences(storePaths, inputPaths), false, true);
+            json[i.key()] = pathInfoToJSON(store,
+                store.exportReferences(storePaths, inputPaths));
         }
     }
 

src/libstore/path-info.cc

@@ -1,3 +1,5 @@
+#include <nlohmann/json.hpp>
+
 #include "path-info.hh"
 #include "store-api.hh"
 
@@ -144,4 +146,46 @@ ValidPathInfo::ValidPathInfo(
     }, std::move(ca).raw);
 }
 
+
+nlohmann::json UnkeyedValidPathInfo::toJSON(
+    const Store & store,
+    bool includeImpureInfo,
+    HashFormat hashFormat) const
+{
+    using nlohmann::json;
+
+    auto jsonObject = json::object();
+
+    jsonObject["valid"] = true;
+    jsonObject["narHash"] = narHash.to_string(hashFormat, true);
+    jsonObject["narSize"] = narSize;
+
+    {
+        auto& jsonRefs = (jsonObject["references"] = json::array());
+        for (auto & ref : references)
+            jsonRefs.emplace_back(store.printStorePath(ref));
+    }
+
+    if (ca)
+        jsonObject["ca"] = renderContentAddress(ca);
+
+    if (includeImpureInfo) {
+        if (deriver)
+            jsonObject["deriver"] = store.printStorePath(*deriver);
+
+        if (registrationTime)
+            jsonObject["registrationTime"] = registrationTime;
+
+        if (ultimate)
+            jsonObject["ultimate"] = ultimate;
+
+        if (!sigs.empty()) {
+            for (auto & sig : sigs)
+                jsonObject["signatures"].push_back(sig);
+        }
+    }
+
+    return jsonObject;
+}
+
 }

src/libstore/path-info.hh

@@ -78,6 +78,18 @@ struct UnkeyedValidPathInfo
     DECLARE_CMP(UnkeyedValidPathInfo);
 
     virtual ~UnkeyedValidPathInfo() { }
+
+    /**
+     * @param includeImpureInfo If true, variable elements such as the
+     * registration time are included.
+     */
+    virtual nlohmann::json toJSON(
+        const Store & store,
+        bool includeImpureInfo,
+        HashFormat hashFormat) const;
+    static UnkeyedValidPathInfo fromJSON(
+        const Store & store,
+        const nlohmann::json & json);
 };
 
 struct ValidPathInfo : UnkeyedValidPathInfo {

src/libstore/store-api.cc

@@ -949,96 +949,6 @@ StorePathSet Store::exportReferences(const StorePathSet & storePaths, const Stor
     return paths;
 }
 
-json Store::pathInfoToJSON(const StorePathSet & storePaths,
-    bool includeImpureInfo, bool showClosureSize,
-    HashFormat hashFormat,
-    AllowInvalidFlag allowInvalid)
-{
-    json::array_t jsonList = json::array();
-
-    for (auto & storePath : storePaths) {
-        auto& jsonPath = jsonList.emplace_back(json::object());
-
-        try {
-            auto info = queryPathInfo(storePath);
-
-            jsonPath["path"] = printStorePath(info->path);
-            jsonPath["valid"] = true;
-            jsonPath["narHash"] = info->narHash.to_string(hashFormat, true);
-            jsonPath["narSize"] = info->narSize;
-
-            {
-                auto& jsonRefs = (jsonPath["references"] = json::array());
-                for (auto & ref : info->references)
-                    jsonRefs.emplace_back(printStorePath(ref));
-            }
-
-            if (info->ca)
-                jsonPath["ca"] = renderContentAddress(info->ca);
-
-            std::pair<uint64_t, uint64_t> closureSizes;
-
-            if (showClosureSize) {
-                closureSizes = getClosureSize(info->path);
-                jsonPath["closureSize"] = closureSizes.first;
-            }
-
-            if (includeImpureInfo) {
-
-                if (info->deriver)
-                    jsonPath["deriver"] = printStorePath(*info->deriver);
-
-                if (info->registrationTime)
-                    jsonPath["registrationTime"] = info->registrationTime;
-
-                if (info->ultimate)
-                    jsonPath["ultimate"] = info->ultimate;
-
-                if (!info->sigs.empty()) {
-                    for (auto & sig : info->sigs)
-                        jsonPath["signatures"].push_back(sig);
-                }
-
-                auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
-                    std::shared_ptr<const ValidPathInfo>(info));
-
-                if (narInfo) {
-                    if (!narInfo->url.empty())
-                        jsonPath["url"] = narInfo->url;
-                    if (narInfo->fileHash)
-                        jsonPath["downloadHash"] = narInfo->fileHash->to_string(hashFormat, true);
-                    if (narInfo->fileSize)
-                        jsonPath["downloadSize"] = narInfo->fileSize;
-                    if (showClosureSize)
-                        jsonPath["closureDownloadSize"] = closureSizes.second;
-                }
-            }
-
-        } catch (InvalidPath &) {
-            jsonPath["path"] = printStorePath(storePath);
-            jsonPath["valid"] = false;
-        }
-    }
-    return jsonList;
-}
-
-
-std::pair<uint64_t, uint64_t> Store::getClosureSize(const StorePath & storePath)
-{
-    uint64_t totalNarSize = 0, totalDownloadSize = 0;
-    StorePathSet closure;
-    computeFSClosure(storePath, closure, false, false);
-    for (auto & p : closure) {
-        auto info = queryPathInfo(p);
-        totalNarSize += info->narSize;
-        auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
-            std::shared_ptr<const ValidPathInfo>(info));
-        if (narInfo)
-            totalDownloadSize += narInfo->fileSize;
-    }
-    return {totalNarSize, totalDownloadSize};
-}
-
 
 const Store::Stats & Store::getStats()
 {

src/libstore/store-api.hh

@@ -80,7 +80,6 @@ typedef std::map<std::string, StorePath> OutputPathMap;
 
 enum CheckSigsFlag : bool { NoCheckSigs = false, CheckSigs = true };
 enum SubstituteFlag : bool { NoSubstitute = false, Substitute = true };
-enum AllowInvalidFlag : bool { DisallowInvalid = false, AllowInvalid = true };
 
 /**
  * Magic header of exportPath() output (obsolete).
@@ -665,28 +664,6 @@ public:
     std::string makeValidityRegistration(const StorePathSet & paths,
         bool showDerivers, bool showHash);
 
-    /**
-     * Write a JSON representation of store path metadata, such as the
-     * hash and the references.
-     *
-     * @param includeImpureInfo If true, variable elements such as the
-     * registration time are included.
-     *
-     * @param showClosureSize If true, the closure size of each path is
-     * included.
-     */
-    nlohmann::json pathInfoToJSON(const StorePathSet & storePaths,
-        bool includeImpureInfo, bool showClosureSize,
-        HashFormat hashFormat = HashFormat::Base32,
-        AllowInvalidFlag allowInvalid = DisallowInvalid);
-
-    /**
-     * @return the size of the closure of the specified path, that is,
-     * the sum of the size of the NAR serialisation of each path in the
-     * closure.
-     */
-    std::pair<uint64_t, uint64_t> getClosureSize(const StorePath & storePath);
-
     /**
      * Optimise the disk space usage of the Nix store by hard-linking files
      * with the same contents.