nix path-info: Add --json flag

Also, factor out JSON generation from value-to-json.{cc,hh}, and
support producing indented JSON.

7 files changed, 472 insertions, 129 deletions

diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 47ee324a6e4f..72e413e4491e 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -1,4 +1,5 @@
 #include "value-to-json.hh"
+#include "json.hh"
 #include "eval-inline.hh"
 #include "util.hh"
 
@@ -8,24 +9,8 @@
 
 namespace nix {
 
-
-void escapeJSON(std::ostream & str, const string & s)
-{
-    str << "\"";
-    for (auto & i : s)
-        if (i == '\"' || i == '\\') str << "\\" << i;
-        else if (i == '\n') str << "\\n";
-        else if (i == '\r') str << "\\r";
-        else if (i == '\t') str << "\\t";
-        else if (i >= 0 && i < 32)
-            str << "\\u" << std::setfill('0') << std::setw(4) << std::hex << (uint16_t) i << std::dec;
-        else str << i;
-    str << "\"";
-}
-
-
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, std::ostream & str, PathSet & context)
+    Value & v, JSONPlaceholder & out, PathSet & context)
 {
     checkInterrupt();
 
@@ -34,58 +19,58 @@ void printValueAsJSON(EvalState & state, bool strict,
     switch (v.type) {
 
         case tInt:
-            str << v.integer;
+            out.write(v.integer);
             break;
 
         case tBool:
-            str << (v.boolean ? "true" : "false");
+            out.write(v.boolean);
             break;
 
         case tString:
             copyContext(v, context);
-            escapeJSON(str, v.string.s);
+            out.write(v.string.s);
             break;
 
         case tPath:
-            escapeJSON(str, state.copyPathToStore(context, v.path));
+            out.write(state.copyPathToStore(context, v.path));
             break;
 
         case tNull:
-            str << "null";
+            out.write(nullptr);
             break;
 
         case tAttrs: {
             Bindings::iterator i = v.attrs->find(state.sOutPath);
             if (i == v.attrs->end()) {
-                JSONObject json(str);
+                auto obj(out.object());
                 StringSet names;
                 for (auto & j : *v.attrs)
                     names.insert(j.name);
                 for (auto & j : names) {
                     Attr & a(*v.attrs->find(state.symbols.create(j)));
-                    json.attr(j);
-                    printValueAsJSON(state, strict, *a.value, str, context);
+                    auto placeholder(obj.placeholder(j));
+                    printValueAsJSON(state, strict, *a.value, placeholder, context);
                 }
             } else
-                printValueAsJSON(state, strict, *i->value, str, context);
+                printValueAsJSON(state, strict, *i->value, out, context);
             break;
         }
 
         case tList1: case tList2: case tListN: {
-            JSONList json(str);
+            auto list(out.list());
             for (unsigned int n = 0; n < v.listSize(); ++n) {
-                json.elem();
-                printValueAsJSON(state, strict, *v.listElems()[n], str, context);
+                auto placeholder(list.placeholder());
+                printValueAsJSON(state, strict, *v.listElems()[n], placeholder, context);
             }
             break;
         }
 
         case tExternal:
-            v.external->printValueAsJSON(state, strict, str, context);
+            v.external->printValueAsJSON(state, strict, out, context);
             break;
 
         case tFloat:
-            str << v.fpoint;
+            out.write(v.fpoint);
             break;
 
         default:
@@ -93,9 +78,15 @@ void printValueAsJSON(EvalState & state, bool strict,
     }
 }
 
+void printValueAsJSON(EvalState & state, bool strict,
+    Value & v, std::ostream & str, PathSet & context)
+{
+    JSONPlaceholder out(str);
+    printValueAsJSON(state, strict, v, out, context);
+}
 
 void ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
-      std::ostream & str, PathSet & context) const
+    JSONPlaceholder & out, PathSet & context) const
 {
     throw TypeError(format("cannot convert %1% to JSON") % showType());
 }
diff --git a/src/libexpr/value-to-json.hh b/src/libexpr/value-to-json.hh
index c59caf5641bc..67fed6487dd9 100644
--- a/src/libexpr/value-to-json.hh
+++ b/src/libexpr/value-to-json.hh
@@ -8,73 +8,12 @@
 
 namespace nix {
 
-void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, std::ostream & out, PathSet & context);
-
-void escapeJSON(std::ostream & str, const string & s);
+class JSONPlaceholder;
 
-struct JSONObject
-{
-    std::ostream & str;
-    bool first;
-    JSONObject(std::ostream & str) : str(str), first(true)
-    {
-        str << "{";
-    }
-    ~JSONObject()
-    {
-        str << "}";
-    }
-    void attr(const string & s)
-    {
-        if (!first) str << ","; else first = false;
-        escapeJSON(str, s);
-        str << ":";
-    }
-    void attr(const string & s, const string & t)
-    {
-        attr(s);
-        escapeJSON(str, t);
-    }
-    void attr(const string & s, const char * t)
-    {
-        attr(s);
-        escapeJSON(str, t);
-    }
-    void attr(const string & s, bool b)
-    {
-        attr(s);
-        str << (b ? "true" : "false");
-    }
-    template<typename T>
-    void attr(const string & s, const T & n)
-    {
-        attr(s);
-        str << n;
-    }
-};
+void printValueAsJSON(EvalState & state, bool strict,
+    Value & v, JSONPlaceholder & out, PathSet & context);
 
-struct JSONList
-{
-    std::ostream & str;
-    bool first;
-    JSONList(std::ostream & str) : str(str), first(true)
-    {
-        str << "[";
-    }
-    ~JSONList()
-    {
-        str << "]";
-    }
-    void elem()
-    {
-        if (!first) str << ","; else first = false;
-    }
-    void elem(const string & s)
-    {
-        elem();
-        escapeJSON(str, s);
-    }
-};
+void printValueAsJSON(EvalState & state, bool strict,
+    Value & v, std::ostream & str, PathSet & context);
 
 }
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 62bdd9281f08..f5e485748812 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -36,6 +36,7 @@ class Symbol;
 struct Pos;
 class EvalState;
 class XMLWriter;
+class JSONPlaceholder;
 
 
 typedef long NixInt;
@@ -73,7 +74,7 @@ class ExternalValueBase
 
     /* Print the value as JSON. Defaults to unconvertable, i.e. throws an error */
     virtual void printValueAsJSON(EvalState & state, bool strict,
-        std::ostream & str, PathSet & context) const;
+        JSONPlaceholder & out, PathSet & context) const;
 
     /* Print the value as XML. Defaults to unevaluated */
     virtual void printValueAsXML(EvalState & state, bool strict, bool location,
diff --git a/src/libutil/json.cc b/src/libutil/json.cc
new file mode 100644
index 000000000000..619b1d631b9a
--- /dev/null
+++ b/src/libutil/json.cc
@@ -0,0 +1,171 @@
+#include "json.hh"
+
+#include <iomanip>
+#include <cstring>
+
+namespace nix {
+
+void toJSON(std::ostream & str, const char * start, const char * end)
+{
+    str << '"';
+    for (auto i = start; i != end; i++)
+        if (*i == '\"' || *i == '\\') str << '\\' << *i;
+        else if (*i == '\n') str << "\\n";
+        else if (*i == '\r') str << "\\r";
+        else if (*i == '\t') str << "\\t";
+        else if (*i >= 0 && *i < 32)
+            str << "\\u" << std::setfill('0') << std::setw(4) << std::hex << (uint16_t) *i << std::dec;
+        else str << *i;
+    str << '"';
+}
+
+void toJSON(std::ostream & str, const std::string & s)
+{
+    toJSON(str, s.c_str(), s.c_str() + s.size());
+}
+
+void toJSON(std::ostream & str, const char * s)
+{
+    if (!s) str << "null"; else toJSON(str, s, s + strlen(s));
+}
+
+void toJSON(std::ostream & str, unsigned long n)
+{
+    str << n;
+}
+
+void toJSON(std::ostream & str, long n)
+{
+    str << n;
+}
+
+void toJSON(std::ostream & str, double f)
+{
+    str << f;
+}
+
+void toJSON(std::ostream & str, bool b)
+{
+    str << (b ? "true" : "false");
+}
+
+JSONWriter::JSONWriter(std::ostream & str, bool indent)
+    : state(new JSONState(str, indent))
+{
+    state->stack.push_back(this);
+}
+
+JSONWriter::JSONWriter(JSONState * state)
+    : state(state)
+{
+    state->stack.push_back(this);
+}
+
+JSONWriter::~JSONWriter()
+{
+    assertActive();
+    state->stack.pop_back();
+    if (state->stack.empty()) delete state;
+}
+
+void JSONWriter::comma()
+{
+    assertActive();
+    if (first) {
+        first = false;
+    } else {
+        state->str << ',';
+    }
+    if (state->indent) indent();
+}
+
+void JSONWriter::indent()
+{
+    state->str << '\n' << std::string(state->depth * 2, ' ');
+}
+
+void JSONList::open()
+{
+    state->depth++;
+    state->str << '[';
+}
+
+JSONList::~JSONList()
+{
+    state->depth--;
+    if (state->indent && !first) indent();
+    state->str << "]";
+}
+
+JSONList JSONList::list()
+{
+    comma();
+    return JSONList(state);
+}
+
+JSONObject JSONList::object()
+{
+    comma();
+    return JSONObject(state);
+}
+
+JSONPlaceholder JSONList::placeholder()
+{
+    comma();
+    return JSONPlaceholder(state);
+}
+
+void JSONObject::open()
+{
+    state->depth++;
+    state->str << '{';
+}
+
+JSONObject::~JSONObject()
+{
+    state->depth--;
+    if (state->indent && !first) indent();
+    state->str << "}";
+}
+
+void JSONObject::attr(const std::string & s)
+{
+    comma();
+    toJSON(state->str, s);
+    state->str << ':';
+    if (state->indent) state->str << ' ';
+}
+
+JSONList JSONObject::list(const std::string & name)
+{
+    attr(name);
+    return JSONList(state);
+}
+
+JSONObject JSONObject::object(const std::string & name)
+{
+    attr(name);
+    return JSONObject(state);
+}
+
+JSONPlaceholder JSONObject::placeholder(const std::string & name)
+{
+    attr(name);
+    return JSONPlaceholder(state);
+}
+
+JSONList JSONPlaceholder::list()
+{
+    assertValid();
+    first = false;
+    return JSONList(state);
+}
+
+JSONObject JSONPlaceholder::object()
+{
+    assertValid();
+    first = false;
+    return JSONObject(state);
+}
+
+}
diff --git a/src/libutil/json.hh b/src/libutil/json.hh
new file mode 100644
index 000000000000..852000a51b38
--- /dev/null
+++ b/src/libutil/json.hh
@@ -0,0 +1,183 @@
+#pragma once
+
+#include <iostream>
+#include <vector>
+#include <cassert>
+
+namespace nix {
+
+void toJSON(std::ostream & str, const char * start, const char * end);
+void toJSON(std::ostream & str, const std::string & s);
+void toJSON(std::ostream & str, const char * s);
+void toJSON(std::ostream & str, unsigned long n);
+void toJSON(std::ostream & str, long n);
+void toJSON(std::ostream & str, double f);
+void toJSON(std::ostream & str, bool b);
+
+class JSONWriter
+{
+protected:
+
+    struct JSONState
+    {
+        std::ostream & str;
+        bool indent;
+        size_t depth = 0;
+        std::vector<JSONWriter *> stack;
+        JSONState(std::ostream & str, bool indent) : str(str), indent(indent) { }
+        ~JSONState()
+        {
+            assert(stack.empty());
+        }
+    };
+
+    JSONState * state;
+
+    bool first = true;
+
+    JSONWriter(std::ostream & str, bool indent);
+
+    JSONWriter(JSONState * state);
+
+    ~JSONWriter();
+
+    void assertActive()
+    {
+        assert(!state->stack.empty() && state->stack.back() == this);
+    }
+
+    void comma();
+
+    void indent();
+};
+
+class JSONObject;
+class JSONPlaceholder;
+
+class JSONList : JSONWriter
+{
+private:
+
+    friend class JSONObject;
+    friend class JSONPlaceholder;
+
+    void open();
+
+    JSONList(JSONState * state)
+        : JSONWriter(state)
+    {
+        open();
+    }
+
+public:
+
+    JSONList(std::ostream & str, bool indent = false)
+        : JSONWriter(str, indent)
+    {
+        open();
+    }
+
+    ~JSONList();
+
+    template<typename T>
+    JSONList & elem(const T & v)
+    {
+        comma();
+        toJSON(state->str, v);
+        return *this;
+    }
+
+    JSONList list();
+
+    JSONObject object();
+
+    JSONPlaceholder placeholder();
+};
+
+class JSONObject : JSONWriter
+{
+private:
+
+    friend class JSONList;
+    friend class JSONPlaceholder;
+
+    void open();
+
+    JSONObject(JSONState * state)
+        : JSONWriter(state)
+    {
+        open();
+    }
+
+    void attr(const std::string & s);
+
+public:
+
+    JSONObject(std::ostream & str, bool indent = false)
+        : JSONWriter(str, indent)
+    {
+        open();
+    }
+
+    ~JSONObject();
+
+    template<typename T>
+    JSONObject & attr(const std::string & name, const T & v)
+    {
+        attr(name);
+        toJSON(state->str, v);
+        return *this;
+    }
+
+    JSONList list(const std::string & name);
+
+    JSONObject object(const std::string & name);
+
+    JSONPlaceholder placeholder(const std::string & name);
+};
+
+class JSONPlaceholder : JSONWriter
+{
+
+private:
+
+    friend class JSONList;
+    friend class JSONObject;
+
+    JSONPlaceholder(JSONState * state)
+        : JSONWriter(state)
+    {
+    }
+
+    void assertValid()
+    {
+        assertActive();
+        assert(first);
+    }
+
+public:
+
+    JSONPlaceholder(std::ostream & str, bool indent = false)
+        : JSONWriter(str, indent)
+    {
+    }
+
+    ~JSONPlaceholder()
+    {
+        assert(!first || std::uncaught_exception());
+    }
+
+    template<typename T>
+    void write(const T & v)
+    {
+        assertValid();
+        first = false;
+        toJSON(state->str, v);
+    }
+
+    JSONList list();
+
+    JSONObject object();
+};
+
+}
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index 955a2466102f..6a557e8ac9db 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -10,6 +10,7 @@
 #include "store-api.hh"
 #include "user-env.hh"
 #include "util.hh"
+#include "json.hh"
 #include "value-to-json.hh"
 #include "xml-writer.hh"
 
@@ -860,26 +861,24 @@ static VersionDiff compareVersionAgainstSet(
 
 static void queryJSON(Globals & globals, vector<DrvInfo> & elems)
 {
-    JSONObject topObj(cout);
+    JSONObject topObj(cout, true);
     for (auto & i : elems) {
-        topObj.attr(i.attrPath);
-        JSONObject pkgObj(cout);
+        JSONObject pkgObj = topObj.object(i.attrPath);
 
         pkgObj.attr("name", i.name);
         pkgObj.attr("system", i.system);
 
-        pkgObj.attr("meta");
-        JSONObject metaObj(cout);
+        JSONObject metaObj = pkgObj.object("meta");
         StringSet metaNames = i.queryMetaNames();
         for (auto & j : metaNames) {
-            metaObj.attr(j);
+            auto placeholder = metaObj.placeholder(j);
             Value * v = i.queryMeta(j);
             if (!v) {
                 printMsg(lvlError, format("derivation ‘%1%’ has invalid meta attribute ‘%2%’") % i.name % j);
-                cout << "null";
+                placeholder.write(nullptr);
             } else {
                 PathSet context;
-                printValueAsJSON(*globals.state, true, *v, cout, context);
+                printValueAsJSON(*globals.state, true, *v, placeholder, context);
             }
         }
     }
diff --git a/src/nix/path-info.cc b/src/nix/path-info.cc
index dca22240b1cb..b25e60db6a3f 100644
--- a/src/nix/path-info.cc
+++ b/src/nix/path-info.cc
@@ -2,6 +2,10 @@
 #include "shared.hh"
 #include "store-api.hh"
 
+
+#include "json.hh"
+
+
 #include <iomanip>
 #include <algorithm>
 
@@ -12,12 +16,14 @@ struct CmdPathInfo : StorePathsCommand
     bool showSize = false;
     bool showClosureSize = false;
     bool showSigs = false;
+    bool json = false;
 
     CmdPathInfo()
     {
         mkFlag('s', "size", "print size of the NAR dump of each path", &showSize);
         mkFlag('S', "closure-size", "print sum size of the NAR dumps of the closure of each path", &showClosureSize);
         mkFlag(0, "sigs", "show signatures", &showSigs);
+        mkFlag(0, "json", "produce JSON output", &json);
     }
 
     std::string name() override
@@ -41,6 +47,10 @@ struct CmdPathInfo : StorePathsCommand
                 "To check the existence of a path in a binary cache:",
                 "nix path-info -r /nix/store/7qvk5c91...-geeqie-1.1 --store https://cache.nixos.org/"
             },
+            Example{
+                "To print the 10 most recently added paths (using --json and the jq(1) command):",
+                "nix path-info --all --json | jq -r 'sort_by(.registrationTime)[-11:-1][].path'"
+            },
         };
     }
 
@@ -50,36 +60,85 @@ struct CmdPathInfo : StorePathsCommand
         for (auto & storePath : storePaths)
             pathLen = std::max(pathLen, storePath.size());
 
-        for (auto storePath : storePaths) {
-            auto info = store->queryPathInfo(storePath);
-            storePath = info->path; // FIXME: screws up padding
+        auto getClosureSize = [&](const Path & storePath) {
+            size_t totalSize = 0;
+            PathSet closure;
+            store->computeFSClosure(storePath, closure, false, false);
+            for (auto & p : closure)
+                totalSize += store->queryPathInfo(p)->narSize;
+            return totalSize;
+        };
 
-            std::cout << storePath << std::string(std::max(0, (int) pathLen - (int) storePath.size()), ' ');
+        if (json) {
+            JSONList jsonRoot(std::cout, true);
 
-            if (showSize) {
-                std::cout << '\t' << std::setw(11) << info->narSize;
-            }
+            for (auto storePath : storePaths) {
+                auto info = store->queryPathInfo(storePath);
+                storePath = info->path;
+
+                auto jsonPath = jsonRoot.object();
+                jsonPath
+                    .attr("path", storePath)
+                    .attr("narHash", info->narHash.to_string())
+                    .attr("narSize", info->narSize);
+
+                if (showClosureSize)
+                    jsonPath.attr("closureSize", getClosureSize(storePath));
+
+                if (info->deriver != "")
+                    jsonPath.attr("deriver", info->deriver);
+
+                {
+                    auto jsonRefs = jsonPath.list("references");
+                    for (auto & ref : info->references)
+                        jsonRefs.elem(ref);
+                }
 
-            if (showClosureSize) {
-                size_t totalSize = 0;
-                PathSet closure;
-                store->computeFSClosure(storePath, closure, false, false);
-                for (auto & p : closure)
-                    totalSize += store->queryPathInfo(p)->narSize;
-                std::cout << '\t' << std::setw(11) << totalSize;
+                if (info->registrationTime)
+                    jsonPath.attr("registrationTime", info->registrationTime);
+
+                if (info->ultimate)
+                    jsonPath.attr("ultimate", info->ultimate);
+
+                if (info->ca != "")
+                    jsonPath.attr("ca", info->ca);
+
+                if (!info->sigs.empty()) {
+                    auto jsonSigs = jsonPath.list("signatures");
+                    for (auto & sig : info->sigs)
+                        jsonSigs.elem(sig);
+                }
             }
+        }
+
+        else {
+
+            for (auto storePath : storePaths) {
+                auto info = store->queryPathInfo(storePath);
+                storePath = info->path; // FIXME: screws up padding
 
-            if (showSigs) {
-                std::cout << '\t';
-                Strings ss;
-                if (info->ultimate) ss.push_back("ultimate");
-                if (info->ca != "") ss.push_back("ca:" + info->ca);
-                for (auto & sig : info->sigs) ss.push_back(sig);
-                std::cout << concatStringsSep(" ", ss);
+                std::cout << storePath << std::string(std::max(0, (int) pathLen - (int) storePath.size()), ' ');
+
+                if (showSize)
+                    std::cout << '\t' << std::setw(11) << info->narSize;
+
+                if (showClosureSize)
+                    std::cout << '\t' << std::setw(11) << getClosureSize(storePath);
+
+                if (showSigs) {
+                    std::cout << '\t';
+                    Strings ss;
+                    if (info->ultimate) ss.push_back("ultimate");
+                    if (info->ca != "") ss.push_back("ca:" + info->ca);
+                    for (auto & sig : info->sigs) ss.push_back(sig);
+                    std::cout << concatStringsSep(" ", ss);
+                }
+
+                std::cout << std::endl;
             }
 
-            std::cout << std::endl;
         }
+
     }
 };