Nix repl flakes

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

@@ -2,3 +2,10 @@
 
 * Nix can now be built with LTO by passing `--enable-lto` to `configure`.
   LTO is currently only supported when building with GCC.
+
+* `nix repl` now takes installables on the command line, unifying the usage
+  with other commands that use `--file` and `--expr`. Primary breaking change
+  is for the common usage of `nix repl '<nixpkgs>'` which can be recovered with
+  `nix repl --file '<nixpkgs>'` or `nix repl --expr 'import <nixpkgs>{}'`
+
+  This is currently guarded by the 'repl-flake' experimental feature

src/libcmd/command.hh

@@ -116,12 +116,13 @@ struct InstallablesCommand : virtual Args, SourceExprCommand
     InstallablesCommand();
 
     void prepare() override;
+    Installables load();
 
     virtual bool useDefaultInstallables() { return true; }
 
     std::optional<FlakeRef> getFlakeRefForCompletion() override;
 
-private:
+protected:
 
     std::vector<std::string> _installables;
 };

src/libcmd/installables.cc

@@ -1033,11 +1033,16 @@ InstallablesCommand::InstallablesCommand()
 
 void InstallablesCommand::prepare()
 {
+    installables = load();
+}
+
+Installables InstallablesCommand::load() {
+    Installables installables;
     if (_installables.empty() && useDefaultInstallables())
         // FIXME: commands like "nix profile install" should not have a
         // default, probably.
         _installables.push_back(".");
-    installables = parseInstallables(getStore(), _installables);
+    return parseInstallables(getStore(), _installables);
 }
 
 std::optional<FlakeRef> InstallablesCommand::getFlakeRefForCompletion()

src/libcmd/installables.hh

@@ -132,6 +132,8 @@ struct Installable
         const std::vector<std::shared_ptr<Installable>> & installables);
 };
 
+typedef std::vector<std::shared_ptr<Installable>> Installables;
+
 struct InstallableValue : Installable
 {
     ref<EvalState> state;

src/libcmd/repl.cc

@@ -22,6 +22,7 @@ extern "C" {
 #include "ansicolor.hh"
 #include "shared.hh"
 #include "eval.hh"
+#include "eval-cache.hh"
 #include "eval-inline.hh"
 #include "attr-path.hh"
 #include "store-api.hh"
@@ -54,6 +55,8 @@ struct NixRepl
     size_t debugTraceIndex;
 
     Strings loadedFiles;
+    typedef std::vector<std::pair<Value*,std::string>> AnnotatedValues;
+    std::function<AnnotatedValues()> getValues;
 
     const static int envSize = 32768;
     std::shared_ptr<StaticEnv> staticEnv;
@@ -63,13 +66,15 @@ struct NixRepl
 
     const Path historyFile;
 
-    NixRepl(ref<EvalState> state);
+    NixRepl(const Strings & searchPath, nix::ref<Store> store,ref<EvalState> state,
+            std::function<AnnotatedValues()> getValues);
     ~NixRepl();
-    void mainLoop(const std::vector<std::string> & files);
+    void mainLoop();
     StringSet completePrefix(const std::string & prefix);
     bool getLine(std::string & input, const std::string & prompt);
     StorePath getDerivationPath(Value & v);
     bool processLine(std::string line);
+
     void loadFile(const Path & path);
     void loadFlake(const std::string & flakeRef);
     void initEnv();
@@ -96,9 +101,11 @@ std::string removeWhitespace(std::string s)
 }
 
 
-NixRepl::NixRepl(ref<EvalState> state)
+NixRepl::NixRepl(const Strings & searchPath, nix::ref<Store> store, ref<EvalState> state,
+            std::function<NixRepl::AnnotatedValues()> getValues)
     : state(state)
     , debugTraceIndex(0)
+    , getValues(getValues)
     , staticEnv(new StaticEnv(false, state->staticBaseEnv.get()))
     , historyFile(getDataDir() + "/nix/repl-history")
 {
@@ -228,18 +235,12 @@ static std::ostream & showDebugTrace(std::ostream & out, const PosTable & positi
     return out;
 }
 
-void NixRepl::mainLoop(const std::vector<std::string> & files)
+void NixRepl::mainLoop()
 {
     std::string error = ANSI_RED "error:" ANSI_NORMAL " ";
     notice("Welcome to Nix " + nixVersion + ". Type :? for help.\n");
 
-    if (!files.empty()) {
-        for (auto & i : files)
-            loadedFiles.push_back(i);
-    }
-
     loadFiles();
-    if (!loadedFiles.empty()) notice("");
 
     // Allow nix-repl specific settings in .inputrc
     rl_readline_name = "nix-repl";
@@ -749,7 +750,6 @@ bool NixRepl::processLine(std::string line)
     return true;
 }
 
-
 void NixRepl::loadFile(const Path & path)
 {
     loadedFiles.remove(path);
@@ -809,13 +809,15 @@ void NixRepl::loadFiles()
     Strings old = loadedFiles;
     loadedFiles.clear();
 
-    bool first = true;
     for (auto & i : old) {
-        if (!first) notice("");
-        first = false;
         notice("Loading '%1%'...", i);
         loadFile(i);
     }
+
+    for (auto & [i, what] : getValues()) {
+        notice("Loading installable '%1%'...", what);
+        addAttrsToScope(*i);
+    }
 }
 
 
@@ -1015,28 +1017,53 @@ void runRepl(
     ref<EvalState>evalState,
     const ValMap & extraEnv)
 {
-    auto repl = std::make_unique<NixRepl>(evalState);
+    auto getValues = [&]()->NixRepl::AnnotatedValues{
+        NixRepl::AnnotatedValues values;
+        return values;
+    };
+    const Strings & searchPath = {};
+    auto repl = std::make_unique<NixRepl>(
+            searchPath,
+            openStore(),
+            evalState,
+            getValues
+        );
 
     repl->initEnv();
 
     // add 'extra' vars.
     for (auto & [name, value] : extraEnv)
         repl->addVarToScope(repl->state->symbols.create(name), *value);
 
-    repl->mainLoop({});
+    repl->mainLoop();
 }
 
-struct CmdRepl : StoreCommand, MixEvalArgs
+struct CmdRepl : InstallablesCommand
 {
+    CmdRepl(){
+        evalSettings.pureEval = false;
+    }
+    void prepare()
+    {
+        if (!settings.isExperimentalFeatureEnabled(Xp::ReplFlake) && !(file) && this->_installables.size() >= 1) {
+            warn("future versions of Nix will require using `--file` to load a file");
+            if (this->_installables.size() > 1)
+                warn("more than one input file is not currently supported");
+            auto filePath = this->_installables[0].data();
+            file = std::optional(filePath);
+            _installables.front() = _installables.back();
+            _installables.pop_back();
+        }
+        installables = InstallablesCommand::load();
+    }
     std::vector<std::string> files;
-
-    CmdRepl()
+    Strings getDefaultFlakeAttrPaths() override
     {
-        expectArgs({
-            .label = "files",
-            .handler = {&files},
-            .completer = completePath
-        });
+        return {""};
+    }
+    virtual bool useDefaultInstallables() override
+    {
+        return file.has_value() or expr.has_value();
     }
 
     bool forceImpureByDefault() override
@@ -1058,12 +1085,37 @@ struct CmdRepl : StoreCommand, MixEvalArgs
 
     void run(ref<Store> store) override
     {
-        auto evalState = make_ref<EvalState>(searchPath, store);
-
-        auto repl = std::make_unique<NixRepl>(evalState);
+        auto state = getEvalState();
+        auto getValues = [&]()->NixRepl::AnnotatedValues{
+            auto installables = load();
+            NixRepl::AnnotatedValues values;
+            for (auto & installable: installables){
+                auto what = installable->what();
+                if (file){
+                    auto [val, pos] = installable->toValue(*state);
+                    auto what = installable->what();
+                    state->forceValue(*val, pos);
+                    auto autoArgs = getAutoArgs(*state);
+                    auto valPost = state->allocValue();
+                    state->autoCallFunction(*autoArgs, *val, *valPost);
+                    state->forceValue(*valPost, pos);
+                    values.push_back( {valPost, what });
+                } else {
+                    auto [val, pos] = installable->toValue(*state);
+                    values.push_back( {val, what} );
+                }
+            }
+            return values;
+        };
+        auto repl = std::make_unique<NixRepl>(
+            searchPath,
+            openStore(),
+            state,
+            getValues
+        );
         repl->autoArgs = getAutoArgs(*repl->state);
         repl->initEnv();
-        repl->mainLoop(files);
+        repl->mainLoop();
     }
 };
 

src/libutil/experimental-features.cc

@@ -13,6 +13,7 @@ std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
     { Xp::RecursiveNix, "recursive-nix" },
     { Xp::NoUrlLiterals, "no-url-literals" },
     { Xp::FetchClosure, "fetch-closure" },
+    { Xp::ReplFlake, "repl-flake" },
 };
 
 const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)

src/libutil/experimental-features.hh

@@ -22,6 +22,7 @@ enum struct ExperimentalFeature
     RecursiveNix,
     NoUrlLiterals,
     FetchClosure,
+    ReplFlake,
 };
 
 /**

src/nix/repl.md

@@ -24,10 +24,34 @@ R""(
 * Interact with Nixpkgs in the REPL:
 
   ```console
-  # nix repl '<nixpkgs>'
+  # nix repl --file example.nix
+  Loading Installable ''...
+  Added 3 variables.
 
-  Loading '<nixpkgs>'...
-  Added 12428 variables.
+  # nix repl --expr '{a={b=3;c=4;};}'
+  Loading Installable ''...
+  Added 1 variables.
+
+  # nix repl --expr '{a={b=3;c=4;};}' a
+  Loading Installable ''...
+  Added 1 variables.
+
+  # nix repl --extra_experimental_features 'flakes repl-flake' nixpkgs
+  Loading Installable 'flake:nixpkgs#'...
+  Added 5 variables.
+
+  nix-repl> legacyPackages.x86_64-linux.emacs.name
+  "emacs-27.1"
+
+  nix-repl> legacyPackages.x86_64-linux.emacs.name
+  "emacs-27.1"
+
+  nix-repl> :q
+
+  # nix repl --expr 'import <nixpkgs>{}'
+
+  Loading Installable ''...
+  Added 12439 variables.
 
   nix-repl> emacs.name
   "emacs-27.1"

tests/repl.sh

@@ -55,15 +55,17 @@ testRepl
 testRepl --store "$TEST_ROOT/store?real=$NIX_STORE_DIR"
 
 testReplResponse () {
-    local response="$(nix repl <<< "$1")"
-    echo "$response" | grep -qs "$2" \
+    local commands="$1"; shift
+    local expectedResponse="$1"; shift
+    local response="$(nix repl "$@" <<< "$commands")"
+    echo "$response" | grep -qs "$expectedResponse" \
       || fail "repl command set:
 
-$1
+$commands
 
 does not respond with:
 
-$2
+$expectedResponse
 
 but with:
 
@@ -76,3 +78,48 @@ testReplResponse '
 :a { a = "2"; }
 "result: ${a}"
 ' "result: 2"
+
+testReplResponse '
+drvPath
+' '".*-simple.drv"' \
+$testDir/simple.nix
+
+testReplResponse '
+drvPath
+' '".*-simple.drv"' \
+--file $testDir/simple.nix --experimental-features 'ca-derivations'
+
+testReplResponse '
+drvPath
+' '".*-simple.drv"' \
+--file $testDir/simple.nix --extra-experimental-features 'repl-flake ca-derivations'
+
+mkdir -p flake && cat <<EOF > flake/flake.nix
+{
+    outputs = { self }: {
+        foo = 1;
+        bar.baz = 2;
+
+        changingThing = "beforeChange";
+    };
+}
+EOF
+testReplResponse '
+foo + baz
+' "3" \
+    ./flake ./flake\#bar --experimental-features 'flakes repl-flake'
+
+# Test the `:reload` mechansim with flakes:
+# - Eval `./flake#changingThing`
+# - Modify the flake
+# - Re-eval it
+# - Check that the result has changed
+replResult=$( (
+echo "changingThing"
+sleep 1 # Leave the repl the time to eval 'foo'
+sed -i 's/beforeChange/afterChange/' flake/flake.nix
+echo ":reload"
+echo "changingThing"
+) | nix repl ./flake --experimental-features 'flakes repl-flake')
+echo "$replResult" | grep -qs beforeChange
+echo "$replResult" | grep -qs afterChange