From 2fd7ee21d11bf7b06aff674663fe618e41eff5e2 Mon Sep 17 00:00:00 2001
From: Tom Bereknyei <tomberek@gmail.com>
Date: Mon, 22 Jan 2024 11:17:08 -0500
Subject: [PATCH] feat: adds --relative flag for relative path resolution in
 shebangs

---
 doc/manual/src/command-ref/nix-shell.md |  5 +++++
 src/nix-build/nix-build.cc              |  8 ++++++--
 tests/functional/nix-shell.sh           | 16 ++++++++++++----
 tests/functional/shell.shebang.expr     |  4 ++++
 4 files changed, 27 insertions(+), 6 deletions(-)
 create mode 100755 tests/functional/shell.shebang.expr

diff --git a/doc/manual/src/command-ref/nix-shell.md b/doc/manual/src/command-ref/nix-shell.md
index 1eaf3c36aa7..470a6a43bd1 100644
--- a/doc/manual/src/command-ref/nix-shell.md
+++ b/doc/manual/src/command-ref/nix-shell.md
@@ -13,6 +13,7 @@
   [`--exclude` *regexp*]
   [`--pure`]
   [`--keep` *name*]
+  [`--relative`]
   {{`--packages` | `-p`} {*packages* | *expressions*} … | [*path*]}
 
 # Disambiguation
@@ -101,6 +102,10 @@ All options not listed here are passed to `nix-store
     When a `--pure` shell is started, keep the listed environment
     variables.
 
+  - `--relative`\
+    If this flag is specified when using the shebang feature, relative paths
+    will be resolved relative to the script's location.
+
 {{#include ./opt-common.md}}
 
 # Environment variables
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 4120ca3cf82..3cfc8b9c2c9 100644
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -107,6 +107,7 @@ static void main_nix_build(int argc, char * * argv)
     auto myName = runEnv ? "nix-shell" : "nix-build";
 
     auto inShebang = false;
+    auto inShebangRelative = false;
     std::string script;
     std::vector<std::string> savedArgs;
 
@@ -206,6 +207,9 @@ static void main_nix_build(int argc, char * * argv)
         else if (runEnv && (*arg == "--packages" || *arg == "-p"))
             packages = true;
 
+        else if (inShebang && (*arg == "--relative")) {
+            inShebangRelative = true;
+        }
         else if (inShebang && *arg == "-i") {
             auto interpreter = getArg(*arg, arg, end);
             interactive = false;
@@ -300,7 +304,7 @@ static void main_nix_build(int argc, char * * argv)
             if (fromArgs)
                 exprs.push_back(state->parseExprFromString(
                     std::move(i),
-                    state->rootPath(CanonPath::fromCwd(inShebang ? dirOf(script) : "."))));
+                    state->rootPath(CanonPath::fromCwd((inShebang && inShebangRelative) ? dirOf(script) : "."))));
             else {
                 auto absolute = i;
                 try {
@@ -313,7 +317,7 @@ static void main_nix_build(int argc, char * * argv)
                     /* If we're in a #! script, interpret filenames
                        relative to the script. */
                     exprs.push_back(state->parseExprFromFile(resolveExprPath(state->checkSourcePath(lookupFileArg(*state,
-                                        inShebang ? absPath(i, absPath(dirOf(script))) : i)))));
+                                        (inShebang && inShebangRelative) ? absPath(i, absPath(dirOf(script))) : i)))));
             }
         }
 
diff --git a/tests/functional/nix-shell.sh b/tests/functional/nix-shell.sh
index 702d3a6b566..ea77df08f6f 100644
--- a/tests/functional/nix-shell.sh
+++ b/tests/functional/nix-shell.sh
@@ -61,13 +61,21 @@ output=$($TEST_ROOT/shell.shebang.sh abc def)
 
 # Test nix-shell shebang mode with an alternate working directory
 sed -e "s|@ENV_PROG@|$(type -P env)|" shell.shebang.expr > $TEST_ROOT/shell.shebang.expr
-chmod a+rx $TEST_ROOT/shell.shebang.expr
+sed -e "s|nix-shell -E|nix-shell --relative -E|" \
+    -e "s|@ENV_PROG@|$(type -P env)|" \
+    shell.shebang.expr > $TEST_ROOT/shell.shebang.expr.relative
+chmod a+rx $TEST_ROOT/shell.shebang.expr{,.relative}
 # Should fail due to expressions using relative path
+pushd ..
 ! $TEST_ROOT/shell.shebang.expr bar
+popd
 cp shell.nix config.nix $TEST_ROOT
-# Should succeed
-output=$($TEST_ROOT/shell.shebang.expr bar)
-[ "$output" = '-e load(ARGV.shift) -- '"$TEST_ROOT"'/shell.shebang.expr bar' ]
+# Should fail
+pushd ..
+! $TEST_ROOT/shell.shebang.expr bar
+output=$($TEST_ROOT/shell.shebang.expr.relative bar)
+popd
+[ "$output" = '-e load(ARGV.shift) -- '"$TEST_ROOT"'/shell.shebang.expr.relative bar' ]
 
 # Test nix-shell shebang mode again with metacharacters in the filename.
 # First word of filename is chosen to not match any file in the test root.
diff --git a/tests/functional/shell.shebang.expr b/tests/functional/shell.shebang.expr
new file mode 100755
index 00000000000..51aef083951
--- /dev/null
+++ b/tests/functional/shell.shebang.expr
@@ -0,0 +1,4 @@
+#! @ENV_PROG@ nix-shell
+#! nix-shell -E "with (import ./shell.nix {}); runCommand \"hi\" {buildInputs = [ruby];} \"\""
+#! nix-shell --pure -i ruby
+puts ARGV[1]