Implement repl-init-files

Closes NixOS#9940

src/libcmd/local.mk

@@ -13,3 +13,5 @@ libcmd_LDFLAGS = $(EDITLINE_LIBS) $(LOWDOWN_LIBS) $(THREAD_LDFLAGS)
 libcmd_LIBS = libstore libutil libexpr libmain libfetchers
 
 $(eval $(call install-file-in, $(buildprefix)$(d)/nix-cmd.pc, $(libdir)/pkgconfig, 0644))
+
+$(d)/repl.cc: $(d)/repl-init-files.nix.gen.hh

src/libcmd/repl-init-files.nix

@@ -0,0 +1,8 @@
+info:
+initial:
+functions:
+let final = builtins.foldl'
+              (prev: function: prev // (function info prev final))
+              initial
+              functions;
+in final

src/libcmd/repl.cc

@@ -43,7 +43,9 @@ extern "C" {
 #include "finally.hh"
 #include "markdown.hh"
 #include "local-fs-store.hh"
-#include "print.hh"
+#include "gc-small-vector.hh"
+#include "fs-input-accessor.hh"
+#include "memory-input-accessor.hh"
 
 #if HAVE_BOEHMGC
 #define GC_INCLUDE_NEW
@@ -114,6 +116,26 @@ struct NixRepl
     void evalString(std::string s, Value & v);
     void loadDebugTraceEnv(DebugTrace & dt);
 
+    /**
+     * Load the `repl-init-file` and add the resulting AttrSet to the top-level
+     * bindings.
+     */
+    void loadReplInitFile();
+    /**
+     * Get the `info` AttrSet that's passed as the first argument to the
+     * `repl-init-file`.
+     */
+    Value * replInitInfo();
+
+    /**
+     * Get the current top-level bindings as an AttrSet.
+     */
+    Value * bindingsToAttrs();
+    /**
+     * Parse a file, evaluate its result, and force the resulting value.
+     */
+    Value * evalFile(SourcePath & path);
+
     void printValue(std::ostream & str,
                               Value & v,
                               unsigned int maxDepth = std::numeric_limits<unsigned int>::max())
@@ -887,6 +909,67 @@ void NixRepl::loadFiles()
         notice("Loading installable '%1%'...", what);
         addAttrsToScope(*i);
     }
+
+    loadReplInitFile();
+}
+
+void NixRepl::loadReplInitFile()
+{
+    if (!evalSettings.replInitFiles) {
+        return;
+    }
+
+    Value * replInits(state->allocValue());
+    state->mkList(*replInits, evalSettings.replInitFiles.get().size());
+    Value ** replInitElems = replInits->listElems();
+
+    size_t i = 0;
+    for (auto path : evalSettings.replInitFiles.get()) {
+        debug("Loading '%1%'...", path);
+        SourcePath sourcePath(makeFSInputAccessor(), CanonPath(path));
+        replInitElems[i] = evalFile(sourcePath);
+        i++;
+    }
+
+    auto evalReplInitFilesPath = CanonPath("repl-init-files.nix");
+    if (!state->corepkgsFS->pathExists(evalReplInitFilesPath)) {
+        state->corepkgsFS->addFile(
+            evalReplInitFilesPath,
+            #include "repl-init-files.nix.gen.hh"
+        );
+    }
+
+    SourcePath evalReplInitFilesSourcePath(state->corepkgsFS, evalReplInitFilesPath);
+    auto replInitFilesFunction = evalFile(evalReplInitFilesSourcePath);
+
+    auto info = replInitInfo();
+
+    auto currentAttrs = bindingsToAttrs();
+
+    Value &newAttrs(*state->allocValue());
+    SmallValueVector<3> args = {info, currentAttrs, replInits};
+    state->callFunction(
+        *replInitFilesFunction,
+        args.size(),
+        args.data(),
+        newAttrs,
+        replInitFilesFunction->determinePos(noPos)
+    );
+
+    addAttrsToScope(newAttrs);
+}
+
+Value * NixRepl::replInitInfo()
+{
+    auto builder = state->buildBindings(1);
+
+    Value * currentSystem(state->allocValue());
+    currentSystem->mkString(evalSettings.getCurrentSystem());
+    builder.insert(state->symbols.create("currentSystem"), currentSystem);
+
+    Value * info(state->allocValue());
+    info->mkAttrs(builder.finish());
+    return info;
 }
 
 
@@ -919,6 +1002,18 @@ void NixRepl::addVarToScope(const Symbol name, Value & v)
     varNames.emplace(state->symbols[name]);
 }
 
+Value * NixRepl::bindingsToAttrs()
+{
+    auto builder = state->buildBindings(staticEnv->vars.size());
+    for (auto & [symbol, displacement] : staticEnv->vars) {
+        builder.insert(symbol, env->values[displacement]);
+    }
+
+    Value * attrs(state->allocValue());
+    attrs->mkAttrs(builder.finish());
+    return attrs;
+}
+
 
 Expr * NixRepl::parseString(std::string s)
 {
@@ -933,6 +1028,15 @@ void NixRepl::evalString(std::string s, Value & v)
     state->forceValue(v, v.determinePos(noPos));
 }
 
+Value * NixRepl::evalFile(SourcePath & path)
+{
+    auto expr = state->parseExprFromFile(path, staticEnv);
+    Value * result(state->allocValue());
+    expr->eval(*state, *env, *result);
+    state->forceValue(*result, result->determinePos(noPos));
+    return result;
+}
+
 
 std::unique_ptr<AbstractNixRepl> AbstractNixRepl::create(
    const SearchPath & searchPath, nix::ref<Store> store, ref<EvalState> state,