Move `shell_words` into its own file

Change-Id: I34c0ebfb6dcea49bf632d8880e04075335a132bf

4 files changed, 111 insertions, 59 deletions

diff --git a/src/libutil/meson.build b/src/libutil/meson.build
index 084d7ed11..91a7b33ba 100644
--- a/src/libutil/meson.build
+++ b/src/libutil/meson.build
@@ -20,6 +20,7 @@ libutil_sources = files(
   'position.cc',
   'references.cc',
   'serialise.cc',
+  'shlex.cc',
   'signals.cc',
   'source-path.cc',
   'suggestions.cc',
@@ -69,6 +70,7 @@ libutil_headers = files(
   'regex-combinators.hh',
   'repair-flag.hh',
   'serialise.hh',
+  'shlex.hh',
   'signals.hh',
   'source-path.hh',
   'split.hh',
diff --git a/src/libutil/shlex.cc b/src/libutil/shlex.cc
new file mode 100644
index 000000000..b5f340251
--- /dev/null
+++ b/src/libutil/shlex.cc
@@ -0,0 +1,77 @@
+#include "shlex.hh"
+#include "util.hh"
+
+namespace nix {
+
+std::vector<std::string> shell_split(const std::string & input)
+{
+    std::vector<std::string> result;
+
+    // Hack: `shell_split` is janky and parses ` a` as `{"", "a"}`, so we trim
+    // whitespace before starting.
+    auto inputTrimmed = trim(input);
+
+    if (inputTrimmed.empty()) {
+        return result;
+    }
+
+    std::regex whitespace("^\\s+");
+    auto begin = inputTrimmed.cbegin();
+    std::string currentToken;
+    enum State { sBegin, sSingleQuote, sDoubleQuote };
+    State state = sBegin;
+    auto iterator = begin;
+
+    for (; iterator != inputTrimmed.cend(); ++iterator) {
+        if (state == sBegin) {
+            std::smatch match;
+            if (regex_search(iterator, inputTrimmed.cend(), match, whitespace)) {
+                currentToken.append(begin, iterator);
+                result.push_back(currentToken);
+                iterator = match[0].second;
+                if (iterator == inputTrimmed.cend()) {
+                    return result;
+                }
+                begin = iterator;
+                currentToken.clear();
+            }
+        }
+
+        switch (*iterator) {
+        case '\'':
+            if (state != sDoubleQuote) {
+                currentToken.append(begin, iterator);
+                begin = iterator + 1;
+                state = state == sBegin ? sSingleQuote : sBegin;
+            }
+            break;
+
+        case '"':
+            if (state != sSingleQuote) {
+                currentToken.append(begin, iterator);
+                begin = iterator + 1;
+                state = state == sBegin ? sDoubleQuote : sBegin;
+            }
+            break;
+
+        case '\\':
+            if (state != sSingleQuote) {
+                // perl shellwords mostly just treats the next char as part
+                // of the string with no special processing
+                currentToken.append(begin, iterator);
+                begin = ++iterator;
+            }
+            break;
+        }
+    }
+
+    if (state != sBegin) {
+        throw ShlexError(input);
+    }
+
+    currentToken.append(begin, iterator);
+    result.push_back(currentToken);
+    return result;
+}
+
+}
diff --git a/src/libutil/shlex.hh b/src/libutil/shlex.hh
new file mode 100644
index 000000000..4e7a48597
--- /dev/null
+++ b/src/libutil/shlex.hh
@@ -0,0 +1,30 @@
+#pragma once
+
+#include <regex>
+#include <string>
+#include <vector>
+
+#include "error.hh"
+
+namespace nix {
+
+class ShlexError : public Error
+{
+public:
+    const std::string input;
+
+    ShlexError(const std::string input)
+        : Error("Failed to parse shell arguments (unterminated quote?): %1%", input)
+        , input(input)
+    {
+    }
+};
+
+/**
+ * Parse a string into shell arguments.
+ *
+ * Takes care of whitespace, quotes, and backslashes (at least a bit).
+ */
+std::vector<std::string> shell_split(const std::string & input);
+
+} // namespace nix
diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 3928e39a9..9a3994842 100644
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -23,70 +23,13 @@
 #include "common-eval-args.hh"
 #include "attr-path.hh"
 #include "legacy.hh"
+#include "shlex.hh"
 
 using namespace nix;
 using namespace std::string_literals;
 
 extern char * * environ __attribute__((weak));
 
-/* Recreate the effect of the perl shellwords function, breaking up a
- * string into arguments like a shell word, including escapes
- */
-static std::vector<std::string> shellwords(const std::string & s)
-{
-    std::regex whitespace("^\\s+");
-    auto begin = s.cbegin();
-    std::vector<std::string> res;
-    std::string cur;
-    enum state {
-        sBegin,
-        sSingleQuote,
-        sDoubleQuote
-    };
-    state st = sBegin;
-    auto it = begin;
-    for (; it != s.cend(); ++it) {
-        if (st == sBegin) {
-            std::smatch match;
-            if (regex_search(it, s.cend(), match, whitespace)) {
-                cur.append(begin, it);
-                res.push_back(cur);
-                it = match[0].second;
-                if (it == s.cend()) return res;
-                begin = it;
-                cur.clear();
-            }
-        }
-        switch (*it) {
-            case '\'':
-                if (st != sDoubleQuote) {
-                    cur.append(begin, it);
-                    begin = it + 1;
-                    st = st == sBegin ? sSingleQuote : sBegin;
-                }
-                break;
-            case '"':
-                if (st != sSingleQuote) {
-                    cur.append(begin, it);
-                    begin = it + 1;
-                    st = st == sBegin ? sDoubleQuote : sBegin;
-                }
-                break;
-            case '\\':
-                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;
-        }
-    }
-    if (st != sBegin) throw Error("unterminated quote in shebang line");
-    cur.append(begin, it);
-    res.push_back(cur);
-    return res;
-}
-
 static void main_nix_build(int argc, char * * argv)
 {
     auto dryRun = false;
@@ -143,7 +86,7 @@ static void main_nix_build(int argc, char * * argv)
                     line = chomp(line);
                     std::smatch match;
                     if (std::regex_match(line, match, std::regex("^#!\\s*nix-shell\\s+(.*)$")))
-                        for (const auto & word : shellwords(match[1].str()))
+                        for (const auto & word : shell_split(match[1].str()))
                             args.push_back(word);
                 }
             }