broken nix print-dev-env on drvs

[manveru]

Describe the bug

nix print-dev-env doesn't work on derivations and store paths anymore. It seems to require a flake reference.

Steps To Reproduce

1. nix run nix/2.15.1#nix -- print-dev-env "$(nix eval --raw nixpkgs#hello.drvPath)"
2. See error

❮ nix run nix/2.15-maintenance#nix -- print-dev-env "$(nix eval --raw nixpkgs#hello.drvPath)"
warning: The interpretation of store paths arguments ending in `.drv` recently changed. If this command is now failing try again with '/nix/store/m7clchh41sryqpiz6x4mbrwhv4n08k3g-hello-2.12.1.drv^*'
error: installable '/nix/store/m7clchh41sryqpiz6x4mbrwhv4n08k3g-hello-2.12.1.drv' does not correspond to a Nix language value
Try '/nix/store/gh0h2cqcp3fnh3s1kcr0kicc7n2sidq1-nix-2.15.1/bin/nix --help' for more information.

Expected behavior

This should print the development environment for the given derivation.

nix-env --version output

nix (Nix) 2.15.0

Additional context

The commit that caused this is 256f3e3

The old behavior is used by https://github.com/divnix/std/blob/63b3a0e83f6a7c9d326f18198b2e6e4110b44816/src/blocktypes/devshells.nix#L55

I made a haphazard patch to fix the issue, but I'm sure there's a better way than duplicating all that code. After trying for a few hours I couldn't make any sense of the C++ errors and gave up on that.

diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 9e2dcff61..28efb9e9a 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -589,7 +589,7 @@ struct CmdDevelop : Common, MixEnvironment
     }
 };

-struct CmdPrintDevEnv : Common, MixJSON
+struct CmdPrintDevEnv : InstallableCommand, MixProfile, MixJSON
 {
     std::string description() override
     {
@@ -603,9 +603,31 @@ struct CmdPrintDevEnv : Common, MixJSON
           ;
     }

+    std::set<std::string> ignoreVars{
+        "BASHOPTS",
+        "HOME", // FIXME: don't ignore in pure mode?
+        "NIX_BUILD_TOP",
+        "NIX_ENFORCE_PURITY",
+        "NIX_LOG_FD",
+        "NIX_REMOTE",
+        "PPID",
+        "SHELL",
+        "SHELLOPTS",
+        "SSL_CERT_FILE", // FIXME: only want to ignore /no-cert-file.crt
+        "TEMP",
+        "TEMPDIR",
+        "TERM",
+        "TMP",
+        "TMPDIR",
+        "TZ",
+        "UID",
+    };
+
+    std::vector<std::pair<std::string, std::string>> redirects;
+
     Category category() override { return catUtility; }

-    void run(ref<Store> store, ref<InstallableValue> installable) override
+    void run(ref<Store> store, ref<Installable> installable) override
     {
         auto buildEnvironment = getBuildEnvironment(store, installable).first;

@@ -616,6 +638,106 @@ struct CmdPrintDevEnv : Common, MixJSON
             ? buildEnvironment.toJSON()
             : makeRcScript(store, buildEnvironment));
     }
+
+    std::pair<BuildEnvironment, std::string>
+    getBuildEnvironment(ref<Store> store, ref<Installable> installable)
+    {
+        auto shellOutPath = getShellOutPath(store, installable);
+
+        auto strPath = store->printStorePath(shellOutPath);
+
+        updateProfile(shellOutPath);
+
+        debug("reading environment file '%s'", strPath);
+
+        return {BuildEnvironment::fromJSON(readFile(store->toRealPath(shellOutPath))), strPath};
+    }
+
+    StorePath getShellOutPath(ref<Store> store, ref<Installable> installable)
+    {
+        auto path = installable->getStorePath();
+        if (path && hasSuffix(path->to_string(), "-env"))
+            return *path;
+        else {
+            auto drvs = Installable::toDerivations(store, {installable});
+
+            if (drvs.size() != 1)
+                throw Error("'%s' needs to evaluate to a single derivation, but it evaluated to %d derivations",
+                    installable->what(), drvs.size());
+
+            auto & drvPath = *drvs.begin();
+
+            return getDerivationEnvironment(store, getEvalStore(), drvPath);
+        }
+    }
+
+    std::string makeRcScript(
+        ref<Store> store,
+        const BuildEnvironment & buildEnvironment,
+        const Path & outputsDir = absPath(".") + "/outputs")
+    {
+        // A list of colon-separated environment variables that should be
+        // prepended to, rather than overwritten, in order to keep the shell usable.
+        // Please keep this list minimal in order to avoid impurities.
+        static const char * const savedVars[] = {
+            "PATH",          // for commands
+            "XDG_DATA_DIRS", // for loadable completion
+        };
+
+        std::ostringstream out;
+
+        out << "unset shellHook\n";
+
+        for (auto & var : savedVars) {
+            out << fmt("%s=${%s:-}\n", var, var);
+            out << fmt("nix_saved_%s=\"$%s\"\n", var, var);
+        }
+
+        buildEnvironment.toBash(out, ignoreVars);
+
+        for (auto & var : savedVars)
+            out << fmt("%s=\"$%s${nix_saved_%s:+:$nix_saved_%s}\"\n", var, var, var, var);
+
+        out << "export NIX_BUILD_TOP=\"$(mktemp -d -t nix-shell.XXXXXX)\"\n";
+        for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
+            out << fmt("export %s=\"$NIX_BUILD_TOP\"\n", i);
+
+        out << "eval \"$shellHook\"\n";
+
+        auto script = out.str();
+
+        /* Substitute occurrences of output paths. */
+        auto outputs = buildEnvironment.vars.find("outputs");
+        assert(outputs != buildEnvironment.vars.end());
+
+        // FIXME: properly unquote 'outputs'.
+        StringMap rewrites;
+        for (auto & outputName : BuildEnvironment::getStrings(outputs->second)) {
+            auto from = buildEnvironment.vars.find(outputName);
+            assert(from != buildEnvironment.vars.end());
+            // FIXME: unquote
+            rewrites.insert({BuildEnvironment::getString(from->second), outputsDir + "/" + outputName});
+        }
+
+        /* Substitute redirects. */
+        for (auto & [installable_, dir_] : redirects) {
+            auto dir = absPath(dir_);
+            auto installable = parseInstallable(store, installable_);
+            auto builtPaths = Installable::toStorePaths(
+                getEvalStore(), store, Realise::Nothing, OperateOn::Output, {installable});
+            for (auto & path: builtPaths) {
+                auto from = store->printStorePath(path);
+                if (script.find(from) == std::string::npos)
+                    warn("'%s' (path '%s') is not used by this build environment", installable->what(), from);
+                else {
+                    printInfo("redirecting '%s' to '%s'", from, dir);
+                    rewrites.insert({from, dir});
+                }
+            }
+        }
+
+        return rewriteStrings(script, rewrites);
+    }
 };

 static auto rCmdPrintDevEnv = registerCommand<CmdPrintDevEnv>("print-dev-env");

@Ericson2314

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[dermetfan]

doesn't work on derivations and store paths anymore. It seems to require a flake reference.

Sounds like this could be the same bug that causes #8284.

EDIT: #8310 but did not fix it so it's a different bug.

[Ericson2314]

Try out #8310