nix-shell: support single quotes in shebangs

Single quotes are a basic feature of shell syntax that people expect to
work. They are also more convenient for writing literal code expressions
with less escaping.

doc/manual/src/command-ref/nix-shell.md

@@ -235,14 +235,14 @@ package like Terraform:
 
 ```bash
 #! /usr/bin/env nix-shell
-#! nix-shell -i bash --packages "terraform.withPlugins (plugins: [ plugins.openstack ])"
+#! nix-shell -i bash --packages 'terraform.withPlugins (plugins: [ plugins.openstack ])'
 
 terraform apply
 ```
 
 > **Note**
 >
-> You must use double quotes (`"`) when passing a simple Nix expression
+> You must use single or double quotes (`'`, `"`) when passing a simple Nix expression
 > in a nix-shell shebang.
 
 Finally, using the merging of multiple nix-shell shebangs the following
@@ -251,7 +251,7 @@ branch):
 
 ```haskell
 #! /usr/bin/env nix-shell
-#! nix-shell -i runghc --packages "haskellPackages.ghcWithPackages (ps: [ps.download-curl ps.tagsoup])"
+#! nix-shell -i runghc --packages 'haskellPackages.ghcWithPackages (ps: [ps.download-curl ps.tagsoup])'
 #! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-20.03.tar.gz
 
 import Network.Curl.Download

doc/manual/src/release-notes/rl-next.md

@@ -12,4 +12,6 @@
 
 - Introduce a new built-in function [`builtins.convertHash`](@docroot@/language/builtins.md#builtins-convertHash).
 
+- `nix-shell` shebang lines now support single-quoted arguments.
+
 - `builtins.fetchTree` is now marked as stable.

src/nix-build/nix-build.cc

@@ -40,7 +40,8 @@ static std::vector<std::string> shellwords(const std::string & s)
     std::string cur;
     enum state {
         sBegin,
-        sQuote
+        sSingleQuote,
+        sDoubleQuote
     };
     state st = sBegin;
     auto it = begin;
@@ -56,15 +57,26 @@ static std::vector<std::string> shellwords(const std::string & s)
             }
         }
         switch (*it) {
+            case '\'':
+                if (st != sDoubleQuote) {
+                    cur.append(begin, it);
+                    begin = it + 1;
+                    st = st == sBegin ? sSingleQuote : sBegin;
+                }
+                break;
             case '"':
-                cur.append(begin, it);
-                begin = it + 1;
-                st = st == sBegin ? sQuote : sBegin;
+                if (st != sSingleQuote) {
+                    cur.append(begin, it);
+                    begin = it + 1;
+                    st = st == sBegin ? sDoubleQuote : sBegin;
+                }
                 break;
             case '\\':
-                /* perl shellwords mostly just treats the next char as part of the string with no special processing */
-                cur.append(begin, it);
-                begin = ++it;
+                if (st != sSingleQuote) {
+                    /* perl shellwords mostly just treats the next char as part of the string with no special processing */
+                    cur.append(begin, it);
+                    begin = ++it;
+                }
                 break;
         }
     }