nix3-develop: correctly escape ASCII control characters for JSON

Fixes #991.
(cherry picked from commit 138c7161be)

Change-Id: Iafc7d9603fbc3615393d32d9630f0e8fe548950b

doc/manual/rl-next/fix-develop-esc.md

@@ -0,0 +1,9 @@
+---
+synopsis: Fix develop shells for derivations with escape codes
+issues: [fj#991]
+cls: [4154, 4155]
+category: Fixes
+credits: [Qyriad]
+---
+
+ASCII control characters (including `\e`, used for ANSI escape codes) in derivation variables are now correctly escaped for `nix develop` and `nix print-dev-env`, instead of erroring.

lix/nix/develop.cc

@@ -142,20 +142,20 @@ struct BuildEnvironment
         for (auto & [name, value] : vars) {
             if (!ignoreVars.count(name)) {
                 if (auto str = std::get_if<String>(&value)) {
-                    out << fmt("%s=%s\n", name, shellEscape(str->value));
+                    out << fmt("%s=%s\n", name, bashEscape(str->value));
                     if (str->exported)
                         out << fmt("export %s\n", name);
                 }
                 else if (auto arr = std::get_if<Array>(&value)) {
                     out << "declare -a " << name << "=(";
                     for (auto & s : *arr)
-                        out << shellEscape(s) << " ";
+                        out << bashEscape(s) << " ";
                     out << ")\n";
                 }
                 else if (auto arr = std::get_if<Associative>(&value)) {
                     out << "declare -A " << name << "=(";
                     for (auto & [n, v] : *arr)
-                        out << "[" << shellEscape(n) << "]=" << shellEscape(v) << " ";
+                        out << "[" << bashEscape(n) << "]=" << bashEscape(v) << " ";
                     out << ")\n";
                 }
             }
@@ -599,21 +599,24 @@ struct CmdDevelop : Common, MixEnvironment
         else if (!command.empty()) {
             std::vector<std::string> args;
             for (auto s : command)
-                args.push_back(shellEscape(s));
+                args.push_back(bashEscape(s));
             script += fmt("exec %s\n", concatStringsSep(" ", args));
         }
 
         else {
             script = "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc;\n" + script;
             if (developSettings.bashPrompt != "")
-                script += fmt("[ -n \"$PS1\" ] && PS1=%s;\n",
-                    shellEscape(developSettings.bashPrompt.get()));
+                script +=
+                    fmt("[ -n \"$PS1\" ] && PS1=%s;\n",
+                        bashEscape(developSettings.bashPrompt.get()));
             if (developSettings.bashPromptPrefix != "")
-                script += fmt("[ -n \"$PS1\" ] && PS1=%s\"$PS1\";\n",
-                    shellEscape(developSettings.bashPromptPrefix.get()));
+                script +=
+                    fmt("[ -n \"$PS1\" ] && PS1=%s\"$PS1\";\n",
+                        bashEscape(developSettings.bashPromptPrefix.get()));
             if (developSettings.bashPromptSuffix != "")
-                script += fmt("[ -n \"$PS1\" ] && PS1+=%s;\n",
-                    shellEscape(developSettings.bashPromptSuffix.get()));
+                script +=
+                    fmt("[ -n \"$PS1\" ] && PS1+=%s;\n",
+                        bashEscape(developSettings.bashPromptSuffix.get()));
         }
 
         writeFull(rcFileFd.get(), script);

lix/nix/get-env.sh

@@ -12,6 +12,31 @@ fi
 __vars="$(declare -p)"
 __functions="$(declare -F)"
 
+# Literal control characters (ASCII 0-31) aren't valid JSON.
+__escapeCtrl() {
+    local escaped="$1"
+
+    # I don't know if NUL bytes are at ALL possible in here,
+    # but covering them is free.
+    local i=0
+    # NOTE: safe input `i` to arithmetic expansion.
+    while [[ "$i" -le 32 ]]; do
+        # Convert the decimal ASCII value to its actual string.
+        local asHex; printf -v asHex "%02x" "$i"
+        local asStr; printf -v asStr "%b" "\x$asHex"
+
+        # Format it to \uXXXX.
+        # All control characters fit within four hex digits.
+        local asUni; printf -v asUni '\\u%04x' "$i"
+
+        escaped="${escaped//"$asStr"/"$asUni"}"
+
+        i="$((i + 1))"
+    done
+
+    printf "%s" "$escaped"
+}
+
 __dumpEnv() {
     printf '{\n'
 
@@ -125,6 +150,7 @@ __escapeString() {
     __s="${__s//$'\n'/\\n}"
     __s="${__s//$'\r'/\\r}"
     __s="${__s//$'\t'/\\t}"
+    __s="$(__escapeCtrl "$__s")"
     printf '"%s"' "$__s"
 }
 

tests/functional/nix-shell/basic.sh

@@ -132,6 +132,7 @@ set -u
     [[ ${arr2[1]} = $'\n' ]]
     [[ ${arr2[2]} = $'x\ny' ]]
     [[ $(fun) = blabla ]]
+    [[ "$ASCII_ESC" = "$(printf "\e")" ]]
     [[ $PATH = $(jq -r .variables.PATH.value $TEST_ROOT/dev-env.json):$path ]]
 )
 

tests/functional/nix-shell/shell.nix

@@ -50,6 +50,7 @@ let pkgs = rec {
     VAR_FROM_NIX = "bar";
     ASCII_PERCENT = "%";
     ASCII_AT = "@";
+    ASCII_ESC = "";
     TEST_inNixShell = if inNixShell then "true" else "false";
     inherit stdenv;
     outputs = ["dev" "out"];