nix print-dev-env: Add --json flag

src/nix/develop.cc

@@ -31,6 +31,11 @@ struct BuildEnvironment
     {
         bool exported;
         std::string value;
+
+        bool operator == (const String & other) const
+        {
+            return exported == other.exported && value == other.value;
+        }
     };
 
     using Array = std::vector<std::string>;
@@ -42,15 +47,13 @@ struct BuildEnvironment
     std::map<std::string, Value> vars;
     std::map<std::string, std::string> bashFunctions;
 
-    static BuildEnvironment fromJSON(const Path & path)
+    static BuildEnvironment fromJSON(std::string_view in)
     {
         BuildEnvironment res;
 
         std::set<std::string> exported;
 
-        debug("reading environment file '%s'", path);
+        auto json = nlohmann::json::parse(in);
-
-        auto json = nlohmann::json::parse(readFile(path));
 
         for (auto & [name, info] : json["variables"].items()) {
             std::string type = info["type"];
@@ -69,6 +72,38 @@ struct BuildEnvironment
         return res;
     }
 
+    std::string toJSON() const
+    {
+        auto res = nlohmann::json::object();
+
+        auto vars2 = nlohmann::json::object();
+        for (auto & [name, value] : vars) {
+            auto info = nlohmann::json::object();
+            if (auto str = std::get_if<String>(&value)) {
+                info["type"] = str->exported ? "exported" : "var";
+                info["value"] = str->value;
+            }
+            else if (auto arr = std::get_if<Array>(&value)) {
+                info["type"] = "array";
+                info["value"] = *arr;
+            }
+            else if (auto arr = std::get_if<Associative>(&value)) {
+                info["type"] = "associative";
+                info["value"] = *arr;
+            }
+            vars2[name] = std::move(info);
+        }
+        res["variables"] = std::move(vars2);
+
+        res["bashFunctions"] = bashFunctions;
+
+        auto json = res.dump();
+
+        assert(BuildEnvironment::fromJSON(json) == *this);
+
+        return json;
+    }
+
     void toBash(std::ostream & out, const std::set<std::string> & ignoreVars) const
     {
         for (auto & [name, value] : vars) {
@@ -116,6 +151,11 @@ struct BuildEnvironment
         else
             throw Error("bash variable is not a string or array");
     }
+
+    bool operator == (const BuildEnvironment & other) const
+    {
+        return vars == other.vars && bashFunctions == other.bashFunctions;
+    }
 };
 
 const static std::string getEnvSh =
@@ -309,7 +349,9 @@ struct Common : InstallableCommand, MixProfile
 
         updateProfile(shellOutPath);
 
-        return {BuildEnvironment::fromJSON(strPath), strPath};
+        debug("reading environment file '%s'", strPath);
+
+        return {BuildEnvironment::fromJSON(readFile(strPath)), strPath};
     }
 };
 
@@ -462,7 +504,7 @@ struct CmdDevelop : Common, MixEnvironment
     }
 };
 
-struct CmdPrintDevEnv : Common
+struct CmdPrintDevEnv : Common, MixJSON
 {
     std::string description() override
     {
@@ -484,7 +526,10 @@ struct CmdPrintDevEnv : Common
 
         stopProgressBar();
 
-        std::cout << makeRcScript(store, buildEnvironment);
+        logger->writeToStdout(
+            json
+            ? buildEnvironment.toJSON()
+            : makeRcScript(store, buildEnvironment));
     }
 };
 

src/nix/get-env.sh

@@ -49,6 +49,7 @@ __dumpEnv() {
               $__var_name = FUNCNAME || \
               $__var_name = HISTCMD || \
               $__var_name = HOSTNAME || \
+              $__var_name = GROUPS || \
               $__var_name = PIPESTATUS || \
               $__var_name = PWD || \
               $__var_name = RANDOM || \

src/nix/print-dev-env.md

@@ -8,12 +8,43 @@ R""(
   # . <(nix print-dev-env nixpkgs#hello)
   ```
 
+* Get the build environment in JSON format:
+
+  ```console
+  # nix print-dev-env nixpkgs#hello --json
+  ```
+
+  The output will look like this:
+
+  ```json
+  {
+    "bashFunctions": {
+      "buildPhase": " \n    runHook preBuild;\n...",
+      ...
+    },
+    "variables": {
+      "src": {
+        "type": "exported",
+        "value": "/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz"
+      },
+      "postUnpackHooks": {
+        "type": "array",
+        "value": ["_updateSourceDateEpochFromSourceRoot"]
+      },
+      ...
+    }
+  }
+  ```
+
 # Description
 
-This command prints a shell script that can be sourced by `b`ash and
+This command prints a shell script that can be sourced by `bash` and
-that sets the environment variables and shell functions defined by the
+that sets the variables and shell functions defined by the build
-build process of *installable*. This allows you to get a similar build
+process of *installable*. This allows you to get a similar build
 environment in your current shell rather than in a subshell (as with
 `nix develop`).
 
+With `--json`, the output is a JSON serialisation of the variables and
+functions defined by the build process.
+
 )""

tests/nix-shell.sh

@@ -96,6 +96,8 @@ echo foo | nix develop -f shell.nix shellDrv -c cat | grep -q foo
 nix_develop -f shell.nix shellDrv -c echo foo |& grep -q foo
 
 # Test 'nix print-dev-env'.
+[[ $(nix print-dev-env -f shell.nix shellDrv --json | jq -r .variables.arr1.value[2]) = '3 4' ]]
+
 source <(nix print-dev-env -f shell.nix shellDrv)
 [[ -n $stdenv ]]
 [[ ${arr1[2]} = "3 4" ]]