From 11e229be732a710812c10c696d0a6df30429a1d1 Mon Sep 17 00:00:00 2001
From: Max <max@privatevoid.net>
Date: Wed, 28 Jun 2023 19:06:25 +0200
Subject: [PATCH] libcmd: add --call-package flag

---
 src/libcmd/command.hh      |  1 +
 src/libcmd/installables.cc | 26 +++++++++++++++++++++-----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
index 2a145e038..99a0f4889 100644
--- a/src/libcmd/command.hh
+++ b/src/libcmd/command.hh
@@ -100,6 +100,7 @@ struct SourceExprCommand : virtual Args, MixFlakeOptions
 {
     std::optional<Path> file;
     std::optional<std::string> expr;
+    std::optional<Path> callPackageFile;
     std::optional<std::string> applyToInstallable;
     std::optional<std::string> installableOverrideAttrs;
     std::optional<std::string> installableWithPackages;
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 6587717e4..d9f3284f7 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -207,6 +207,19 @@ SourceExprCommand::SourceExprCommand()
         .handler = {&expr}
     });
 
+    addFlag({
+        .longName = "call-package",
+        .shortName = 'C',
+        .description =
+            "Interpret [*installables*](@docroot@/command-ref/new-cli/nix.md#installables) as attribute paths relative to the callPackageable Nix expression stored in *file*. "
+            "The `callPackage` function is taken from `<nixpkgs>`. "
+            "Implies `--impure`.",
+        .category = installablesCategory,
+        .labels = {"file"},
+        .handler = {&callPackageFile},
+        .completer = completePath
+    });
+
     addFlag({
         .longName = "apply-to-installable",
         .description = "Apply the function *expr* to each installable.",
@@ -542,12 +555,12 @@ Installables SourceExprCommand::parseInstallables(
     auto doModifyInstallable = applyOverrides && ( applyToInstallable
         || installableOverrideAttrs || installableWithPackages || overrideArgs.size() > 0 );
 
-    if (nestedIsExprOk && (file || expr)) {
-        if (file && expr)
-            throw UsageError("'--file' and '--expr' are exclusive");
+    if (nestedIsExprOk && (file || expr || callPackageFile)) {
+        if ((file && expr) || (file && callPackageFile) || (expr && callPackageFile))
+            throw UsageError("'--file', '--expr' and '--call-package' are exclusive");
 
         // FIXME: backward compatibility hack
-        if (file) evalSettings.pureEval = false;
+        if (file || callPackageFile) evalSettings.pureEval = false;
 
         auto state = getEvalState();
         auto vFile = state->allocValue();
@@ -558,7 +571,10 @@ Installables SourceExprCommand::parseInstallables(
         }
         else if (file)
             state->evalFile(lookupFileArg(*state, *file), *vFile);
-        else {
+        else if (callPackageFile) {
+            auto e = state->parseExprFromString(fmt("(import <nixpkgs> {}).callPackage %s {}", CanonPath::fromCwd(*callPackageFile)), state->rootPath(CanonPath::fromCwd()));
+            state->eval(e, *vFile);
+        } else {
             auto e = state->parseExprFromString(*expr, state->rootPath(CanonPath::fromCwd()));
             state->eval(e, *vFile);
         }