Merge pull request #10122 from edolstra/arg-from-file

Add --arg-from-file and --arg-from-stdin

doc/manual/rl-next/arg-from-file.md

@@ -0,0 +1,9 @@
+---
+synopsis: "CLI options `--arg-from-file` and `--arg-from-stdin`"
+prs: 10122
+---
+
+The new CLI option `--arg-from-file` *name* *path* passes the contents
+of file *path* as a string value via the function argument *name* to a
+Nix expression. Similarly, the new option `--arg-from-stdin` *name*
+reads the contents of the string from standard input.

src/libcmd/common-eval-args.cc

@@ -20,7 +20,7 @@ MixEvalArgs::MixEvalArgs()
         .description = "Pass the value *expr* as the argument *name* to Nix functions.",
         .category = category,
         .labels = {"name", "expr"},
-        .handler = {[&](std::string name, std::string expr) { autoArgs[name] = 'E' + expr; }}
+        .handler = {[&](std::string name, std::string expr) { autoArgs.insert_or_assign(name, AutoArg{AutoArgExpr(expr)}); }}
     });
 
     addFlag({
@@ -28,7 +28,24 @@ MixEvalArgs::MixEvalArgs()
         .description = "Pass the string *string* as the argument *name* to Nix functions.",
         .category = category,
         .labels = {"name", "string"},
-        .handler = {[&](std::string name, std::string s) { autoArgs[name] = 'S' + s; }},
+        .handler = {[&](std::string name, std::string s) { autoArgs.insert_or_assign(name, AutoArg{AutoArgString(s)}); }},
+    });
+
+    addFlag({
+        .longName = "arg-from-file",
+        .description = "Pass the contents of file *path* as the argument *name* to Nix functions.",
+        .category = category,
+        .labels = {"name", "path"},
+        .handler = {[&](std::string name, std::string path) { autoArgs.insert_or_assign(name, AutoArg{AutoArgFile(path)}); }},
+        .completer = completePath
+    });
+
+    addFlag({
+        .longName = "arg-from-stdin",
+        .description = "Pass the contents of stdin as the argument *name* to Nix functions.",
+        .category = category,
+        .labels = {"name"},
+        .handler = {[&](std::string name) { autoArgs.insert_or_assign(name, AutoArg{AutoArgStdin{}}); }},
     });
 
     addFlag({
@@ -154,13 +171,23 @@ MixEvalArgs::MixEvalArgs()
 Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
 {
     auto res = state.buildBindings(autoArgs.size());
-    for (auto & i : autoArgs) {
+    for (auto & [name, arg] : autoArgs) {
         auto v = state.allocValue();
-        if (i.second[0] == 'E')
-            state.mkThunk_(*v, state.parseExprFromString(i.second.substr(1), state.rootPath(".")));
-        else
-            v->mkString(((std::string_view) i.second).substr(1));
-        res.insert(state.symbols.create(i.first), v);
+        std::visit(overloaded {
+            [&](const AutoArgExpr & arg) {
+                state.mkThunk_(*v, state.parseExprFromString(arg.expr, state.rootPath(".")));
+            },
+            [&](const AutoArgString & arg) {
+                v->mkString(arg.s);
+            },
+            [&](const AutoArgFile & arg) {
+                v->mkString(readFile(arg.path));
+            },
+            [&](const AutoArgStdin & arg) {
+                v->mkString(readFile(STDIN_FILENO));
+            }
+        }, arg);
+        res.insert(state.symbols.create(name), v);
     }
     return res.finish();
 }

src/libcmd/common-eval-args.hh

@@ -6,6 +6,8 @@
 #include "common-args.hh"
 #include "search-path.hh"
 
+#include <filesystem>
+
 namespace nix {
 
 class Store;
@@ -26,7 +28,14 @@ struct MixEvalArgs : virtual Args, virtual MixRepair
     std::optional<std::string> evalStoreUrl;
 
 private:
-    std::map<std::string, std::string> autoArgs;
+    struct AutoArgExpr { std::string expr; };
+    struct AutoArgString { std::string s; };
+    struct AutoArgFile { std::filesystem::path path; };
+    struct AutoArgStdin { };
+
+    using AutoArg = std::variant<AutoArgExpr, AutoArgString, AutoArgFile, AutoArgStdin>;
+
+    std::map<std::string, AutoArg> autoArgs;
 };
 
 SourcePath lookupFileArg(EvalState & state, std::string_view s, const Path * baseDir = nullptr);

tests/functional/eval.sh

@@ -41,3 +41,14 @@ mkdir -p $TEST_ROOT/xyzzy $TEST_ROOT/foo
 ln -sfn ../xyzzy $TEST_ROOT/foo/bar
 printf 123 > $TEST_ROOT/xyzzy/default.nix
 [[ $(nix eval --impure --expr "import $TEST_ROOT/foo/bar") = 123 ]]
+
+# Test --arg-from-file.
+[[ "$(nix eval --raw --arg-from-file foo config.nix --expr '{ foo }: { inherit foo; }' foo)" = "$(cat config.nix)" ]]
+
+# Check that special(-ish) files are drained.
+if [[ -e /proc/version ]]; then
+    [[ "$(nix eval --raw --arg-from-file foo /proc/version --expr '{ foo }: { inherit foo; }' foo)" = "$(cat /proc/version)" ]]
+fi
+
+# Test --arg-from-stdin.
+[[ "$(echo bla | nix eval --raw --arg-from-stdin foo --expr '{ foo }: { inherit foo; }' foo)" = bla ]]