Merge pull request #12652 from roberth/cli-json-pretty

nix-cli: Add --json --pretty / --no-pretty

src/libmain/common-args.cc

@@ -1,3 +1,5 @@
+#include <nlohmann/json.hpp>
+
 #include "common-args.hh"
 #include "args/root.hh"
 #include "config-global.hh"
@@ -93,5 +95,18 @@ void MixCommonArgs::initialFlagsProcessed()
     pluginsInited();
 }
 
-
+template <typename T, typename>
+void MixPrintJSON::printJSON(const T /* nlohmann::json */ & json)
+{
+    auto suspension = logger->suspend();
+    if (outputPretty) {
+        logger->writeToStdout(json.dump(2));
+    } else {
+        logger->writeToStdout(json.dump());
+    }
 }
+
+template void MixPrintJSON::printJSON(const nlohmann::json & json);
+
+
+} // namespace nix

src/libmain/common-args.hh

@@ -29,13 +29,69 @@ struct MixDryRun : virtual Args
         addFlag({
             .longName = "dry-run",
             .description = "Show what this command would do without doing it.",
-            //.category = commonArgsCategory,
             .handler = {&dryRun, true},
         });
     }
 };
 
-struct MixJSON : virtual Args
+/**
+ * Commands that can print JSON according to the
+ * `--pretty`/`--no-pretty` flag.
+ *
+ * This is distinct from MixJSON, because for some commands,
+ * JSON outputs is not optional.
+ */
+struct MixPrintJSON : virtual Args
+{
+    bool outputPretty = isatty(STDOUT_FILENO);
+
+    MixPrintJSON()
+    {
+        addFlag({
+            .longName = "pretty",
+            .description =
+                R"(
+                    Print multi-line, indented JSON output for readability.
+
+                    Default: indent if output is to a terminal.
+
+                    This option is only effective when `--json` is also specified.
+                )",
+            .handler = {&outputPretty, true},
+        });
+        addFlag({
+            .longName = "no-pretty",
+            .description =
+                R"(
+                    Print compact JSON output on a single line, even when the output is a terminal.
+                    Some commands may print multiple JSON objects on separate lines.
+
+                    See `--pretty`.
+                )",
+            .handler = {&outputPretty, false},
+        });
+    };
+
+    /**
+     * Print an `nlohmann::json` to stdout
+     *
+     * - respecting `--pretty` / `--no-pretty`.
+     * - suspending the progress bar
+     *
+     * This is a template to avoid accidental coercions from `string` to `json` in the caller,
+     * to avoid mistakenly passing an already serialized JSON to this function.
+     *
+     * It is not recommended to print a JSON string - see the JSON guidelines
+     * about extensibility, https://nix.dev/manual/nix/development/development/json-guideline.html -
+     * but you _can_ print a sole JSON string by explicitly coercing it to
+     * `nlohmann::json` first.
+     */
+    template <typename T, typename = std::enable_if_t<std::is_same_v<T, nlohmann::json>>>
+    void printJSON(const T & json);
+};
+
+/** Optional JSON support via `--json` flag */
+struct MixJSON : virtual Args, virtual MixPrintJSON
 {
     bool json = false;
 
@@ -44,7 +100,6 @@ struct MixJSON : virtual Args
         addFlag({
             .longName = "json",
             .description = "Produce output in JSON format, suitable for consumption by another program.",
-            //.category = commonArgsCategory,
             .handler = {&json, true},
         });
     }

src/nix/build.cc

@@ -101,7 +101,7 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixJSON, MixProfile
             printMissing(store, pathsToBuild, lvlError);
 
             if (json)
-                logger->cout("%s", derivedPathsToJSON(pathsToBuild, *store).dump());
+                printJSON(derivedPathsToJSON(pathsToBuild, *store));
 
             return;
         }

src/nix/config.cc

@@ -63,7 +63,7 @@ struct CmdConfigShow : Command, MixJSON
 
         if (json) {
             // FIXME: use appropriate JSON types (bool, ints, etc).
-            logger->cout("%s", globalConfig.toJSON().dump());
+            printJSON(globalConfig.toJSON());
         } else {
             logger->cout("%s", globalConfig.toKeyValue());
         }

src/nix/derivation-show.cc

@@ -11,7 +11,7 @@
 using namespace nix;
 using json = nlohmann::json;
 
-struct CmdShowDerivation : InstallablesCommand
+struct CmdShowDerivation : InstallablesCommand, MixPrintJSON
 {
     bool recursive = false;
 
@@ -57,7 +57,7 @@ struct CmdShowDerivation : InstallablesCommand
             jsonRoot[store->printStorePath(drvPath)] =
                 store->readDerivation(drvPath).toJSON(*store);
         }
-        logger->cout(jsonRoot.dump(2));
+        printJSON(jsonRoot);
     }
 };
 

src/nix/develop.cc

@@ -63,14 +63,12 @@ struct BuildEnvironment
     std::map<std::string, std::string> bashFunctions;
     std::optional<std::pair<std::string, std::string>> structuredAttrs;
 
-    static BuildEnvironment fromJSON(std::string_view in)
+    static BuildEnvironment fromJSON(const nlohmann::json & json)
     {
         BuildEnvironment res;
 
         std::set<std::string> exported;
 
-        auto json = nlohmann::json::parse(in);
-
         for (auto & [name, info] : json["variables"].items()) {
             std::string type = info["type"];
             if (type == "var" || type == "exported")
@@ -92,7 +90,14 @@ struct BuildEnvironment
         return res;
     }
 
-    std::string toJSON() const
+    static BuildEnvironment parseJSON(std::string_view in)
+    {
+        auto json = nlohmann::json::parse(in);
+
+        return fromJSON(json);
+    }
+
+    nlohmann::json toJSON() const
     {
         auto res = nlohmann::json::object();
 
@@ -124,11 +129,9 @@ struct BuildEnvironment
             res["structuredAttrs"] = std::move(contents);
         }
 
-        auto json = res.dump();
+        assert(BuildEnvironment::fromJSON(res) == *this);
 
-        assert(BuildEnvironment::fromJSON(json) == *this);
+        return res;
-
-        return json;
     }
 
     bool providesStructuredAttrs() const
@@ -505,7 +508,7 @@ struct Common : InstallableCommand, MixProfile
 
         debug("reading environment file '%s'", strPath);
 
-        return {BuildEnvironment::fromJSON(readFile(store->toRealPath(shellOutPath))), strPath};
+        return {BuildEnvironment::parseJSON(readFile(store->toRealPath(shellOutPath))), strPath};
     }
 };
 
@@ -733,7 +736,7 @@ struct CmdPrintDevEnv : Common, MixJSON
         logger->stop();
 
         if (json) {
-            logger->writeToStdout(buildEnvironment.toJSON());
+            printJSON(buildEnvironment.toJSON());
         } else {
             AutoDelete tmpDir(createTempDir("", "nix-dev-env"), true);
             logger->writeToStdout(makeRcScript(store, buildEnvironment, tmpDir));

src/nix/eval.cc

@@ -118,7 +118,7 @@ struct CmdEval : MixJSON, InstallableValueCommand, MixReadOnlyOption
         }
 
         else if (json) {
-            logger->cout("%s", printValueAsJSON(*state, true, *v, pos, context, false));
+            printJSON(printValueAsJSON(*state, true, *v, pos, context, false));
         }
 
         else {

src/nix/flake.cc

@@ -242,7 +242,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
             j["locks"] = lockedFlake.lockFile.toJSON().first;
             if (auto fingerprint = lockedFlake.getFingerprint(store, fetchSettings))
                 j["fingerprint"] = fingerprint->to_string(HashFormat::Base16, false);
-            logger->cout("%s", j.dump());
+            printJSON(j);
         } else {
             logger->cout(
                 ANSI_BOLD "Resolved URL:" ANSI_NORMAL "  %s",
@@ -1115,7 +1115,7 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun
                 {"path", store->printStorePath(storePath)},
                 {"inputs", traverse(*flake.lockFile.root)},
             };
-            logger->cout("%s", jsonRoot);
+            printJSON(jsonRoot);
         } else {
             traverse(*flake.lockFile.root);
         }
@@ -1427,7 +1427,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
         auto j = visit(*cache->getRoot(), {}, fmt(ANSI_BOLD "%s" ANSI_NORMAL, flake->flake.lockedRef), "");
         if (json)
-            logger->cout("%s", j.dump());
+            printJSON(j);
     }
 };
 
@@ -1473,7 +1473,7 @@ struct CmdFlakePrefetch : FlakeCommand, MixJSON
             res["hash"] = hash.to_string(HashFormat::SRI, true);
             res["original"] = fetchers::attrsToJSON(resolvedRef.toAttrs());
             res["locked"] = fetchers::attrsToJSON(lockedRef.toAttrs());
-            logger->cout(res.dump());
+            printJSON(res);
         } else {
             notice("Downloaded '%s' to '%s' (hash '%s').",
                 lockedRef.to_string(),

src/nix/make-content-addressed.cc

@@ -44,7 +44,7 @@ struct CmdMakeContentAddressed : virtual CopyCommand, virtual StorePathsCommand,
             }
             auto json = json::object();
             json["rewrites"] = jsonRewrites;
-            logger->cout("%s", json);
+            printJSON(json);
         } else {
             for (auto & path : storePaths) {
                 auto i = remappings.find(path);

src/nix/path-info.cc

@@ -154,11 +154,11 @@ struct CmdPathInfo : StorePathsCommand, MixJSON
             pathLen = std::max(pathLen, store->printStorePath(storePath).size());
 
         if (json) {
-            logger->cout(pathInfoToJSON(
+            printJSON(pathInfoToJSON(
                 *store,
                 // FIXME: preserve order?
                 StorePathSet(storePaths.begin(), storePaths.end()),
-                showClosureSize).dump());
+                showClosureSize));
         }
 
         else {

src/nix/prefetch.cc

@@ -326,7 +326,7 @@ struct CmdStorePrefetchFile : StoreCommand, MixJSON
             auto res = nlohmann::json::object();
             res["storePath"] = store->printStorePath(storePath);
             res["hash"] = hash.to_string(HashFormat::SRI, true);
-            logger->cout(res.dump());
+            printJSON(res);
         } else {
             notice("Downloaded '%s' to '%s' (hash '%s').",
                 url,

src/nix/profile.cc

@@ -802,7 +802,7 @@ struct CmdProfileList : virtual EvalCommand, virtual StoreCommand, MixDefaultPro
         ProfileManifest manifest(*getEvalState(), *profile);
 
         if (json) {
-            std::cout << manifest.toJSON(*store).dump() << "\n";
+            printJSON(manifest.toJSON(*store));
         } else {
             for (const auto & [i, e] : enumerate(manifest.elements)) {
                 auto & [name, element] = e;

src/nix/realisation.cc

@@ -57,7 +57,7 @@ struct CmdRealisationInfo : BuiltPathsCommand, MixJSON
 
                 res.push_back(currentPath);
             }
-            logger->cout("%s", res);
+            printJSON(res);
         }
         else {
             for (auto & path : realisations) {

src/nix/search.cc

@@ -198,7 +198,7 @@ struct CmdSearch : InstallableValueCommand, MixJSON
             visit(*cursor, cursor->getAttrPath(), true);
 
         if (json)
-            logger->cout("%s", *jsonOut);
+            printJSON(*jsonOut);
 
         if (!json && !results)
             throw Error("no results for the given search term(s)!");

src/nix/store-info.cc

@@ -33,7 +33,7 @@ struct CmdPingStore : StoreCommand, MixJSON
         } else {
             nlohmann::json res;
             Finally printRes([&]() {
-                logger->cout("%s", res);
+                printJSON(res);
             });
 
             res["url"] = store->getUri();

tests/functional/json.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+# Meson would split the output into two buffers, ruining the coherence of the log.
+exec 1>&2
+
+cat > "$TEST_HOME/expected-machine.json" <<EOF
+{"a":{"b":{"c":true}}}
+EOF
+
+cat > "$TEST_HOME/expected-pretty.json" <<EOF
+{
+  "a": {
+    "b": {
+      "c": true
+    }
+  }
+}
+EOF
+
+nix eval --json --expr '{ a.b.c = true; }' > "$TEST_HOME/actual.json"
+diff -U3 "$TEST_HOME/expected-machine.json" "$TEST_HOME/actual.json"
+
+nix eval --json --pretty --expr \
+  '{ a.b.c = true; }' > "$TEST_HOME/actual.json"
+diff -U3 "$TEST_HOME/expected-pretty.json" "$TEST_HOME/actual.json"
+
+if type script &>/dev/null; then
+  script --return --quiet --command 'nix eval --json --expr "{ a.b.c = true; }"' > "$TEST_HOME/actual.json"
+  cat "$TEST_HOME/actual.json"
+  # script isn't perfectly accurate? Let's grep for a pretty good indication, as the pretty output has a space between the key and the value.
+  # diff -U3 "$TEST_HOME/expected-pretty.json" "$TEST_HOME/actual.json"
+  grep -F '"a": {' "$TEST_HOME/actual.json"
+
+  script --return --quiet --command 'nix eval --json --pretty --expr "{ a.b.c = true; }"' > "$TEST_HOME/actual.json"
+  cat "$TEST_HOME/actual.json"
+  grep -F '"a": {' "$TEST_HOME/actual.json"
+
+  script --return --quiet --command 'nix eval --json --no-pretty --expr "{ a.b.c = true; }"' > "$TEST_HOME/actual.json"
+  cat "$TEST_HOME/actual.json"
+  grep -F '"a":{' "$TEST_HOME/actual.json"
+
+fi

tests/functional/meson.build

@@ -157,6 +157,7 @@ suites = [
       'impure-derivations.sh',
       'path-from-hash-part.sh',
       'path-info.sh',
+      'json.sh',
       'toString-path.sh',
       'read-only-store.sh',
       'nested-sandboxing.sh',