Shell: Add a 'setopt' builtin

This builtin sets (and unsets) boolean flags that alter the behaviour of
the shell.
The only flags added are
- inline_exec_keep_empty_segments: Keep empty segments in the result of
  splitting $(...) by $IFS
- verbose: Announce each command before executing it

It should be noted that the (rather extreme) verbosity of the names is
intentional, and will hopefully be alleviated by the next commit :^)

Shell/AST.cpp

@@ -818,7 +818,7 @@ RefPtr<Value> Execute::run(RefPtr<Shell> shell)
             dbg() << "close() failed: " << strerror(errno);
         }
 
-        return create<StringValue>(builder.build(), shell->local_variable_or("IFS", "\n"));
+        return create<StringValue>(builder.build(), shell->local_variable_or("IFS", "\n"), shell->options.inline_exec_keep_empty_segments);
     }
 
     run_commands(commands);
@@ -1799,7 +1799,7 @@ StringValue::~StringValue()
 Vector<String> StringValue::resolve_as_list(RefPtr<Shell>)
 {
     if (is_list()) {
-        auto parts = StringView(m_string).split_view(m_split);
+        auto parts = StringView(m_string).split_view(m_split, m_keep_empty);
         Vector<String> result;
         result.ensure_capacity(parts.size());
         for (auto& part : parts)

Shell/AST.h

@@ -238,15 +238,17 @@ public:
     virtual ~StringValue();
     virtual bool is_string() const override { return m_split.is_null(); }
     virtual bool is_list() const override { return !m_split.is_null(); }
-    StringValue(String string, String split_by = {})
+    StringValue(String string, String split_by = {}, bool keep_empty = false)
         : m_string(string)
         , m_split(move(split_by))
+        , m_keep_empty(keep_empty)
     {
     }
 
 private:
     String m_string;
     String m_split;
+    bool m_keep_empty { false };
 };
 
 class GlobValue final : public Value {

Shell/Builtin.cpp

@@ -645,6 +645,45 @@ int Shell::builtin_pwd(int, const char**)
     return 0;
 }
 
+int Shell::builtin_setopt(int argc, const char** argv)
+{
+    if (argc == 1) {
+#define __ENUMERATE_SHELL_OPTION(name, default_, description) \
+    if (options.name)                                         \
+        fprintf(stderr, #name "\n");
+
+        ENUMERATE_SHELL_OPTIONS();
+
+#undef __ENUMERATE_SHELL_OPTION
+    }
+
+    Core::ArgsParser parser;
+#define __ENUMERATE_SHELL_OPTION(name, default_, description)     \
+    bool name = false;                                            \
+    bool not_##name = false;                                      \
+    parser.add_option(name, "Enable: " description, #name, '\0'); \
+    parser.add_option(not_##name, "Disable: " description, "no_" #name, '\0');
+
+    ENUMERATE_SHELL_OPTIONS();
+
+#undef __ENUMERATE_SHELL_OPTION
+
+    if (!parser.parse(argc, const_cast<char**>(argv), false))
+        return 1;
+
+#define __ENUMERATE_SHELL_OPTION(name, default_, description) \
+    if (name)                                                 \
+        options.name = true;                                  \
+    if (not_##name)                                           \
+        options.name = false;
+
+    ENUMERATE_SHELL_OPTIONS();
+
+#undef __ENUMERATE_SHELL_OPTION
+
+    return 0;
+}
+
 int Shell::builtin_time(int argc, const char** argv)
 {
     Vector<const char*> args;

Shell/Shell.cpp

@@ -356,6 +356,14 @@ RefPtr<Job> Shell::run_command(AST::Command& command)
 {
     FileDescriptionCollector fds;
 
+    if (options.verbose) {
+        fprintf(stderr, "+ ");
+        for (auto& arg : command.argv)
+            fprintf(stderr, "%s ", escape_token(arg).characters());
+        fprintf(stderr, "\n");
+        fflush(stderr);
+    }
+
     // Resolve redirections.
     NonnullRefPtrVector<AST::Rewiring> rewirings;
     for (auto& redirection : command.redirections) {

Shell/Shell.h

@@ -52,12 +52,17 @@
     __ENUMERATE_SHELL_BUILTIN(dirs)    \
     __ENUMERATE_SHELL_BUILTIN(pushd)   \
     __ENUMERATE_SHELL_BUILTIN(popd)    \
+    __ENUMERATE_SHELL_BUILTIN(setopt)  \
     __ENUMERATE_SHELL_BUILTIN(time)    \
     __ENUMERATE_SHELL_BUILTIN(jobs)    \
     __ENUMERATE_SHELL_BUILTIN(disown)  \
     __ENUMERATE_SHELL_BUILTIN(fg)      \
     __ENUMERATE_SHELL_BUILTIN(bg)
 
+#define ENUMERATE_SHELL_OPTIONS()                                                                                    \
+    __ENUMERATE_SHELL_OPTION(inline_exec_keep_empty_segments, false, "Keep empty segments in inline execute $(...)") \
+    __ENUMERATE_SHELL_OPTION(verbose, false, "Announce every command that is about to be executed")
+
 class Shell;
 
 class Shell : public Core::Object {
@@ -135,6 +140,15 @@ public:
         ReadLine,
     };
 
+#define __ENUMERATE_SHELL_OPTION(name, default_, description) \
+    bool name { default_ };
+
+    struct Options {
+        ENUMERATE_SHELL_OPTIONS();
+    } options;
+
+#undef __ENUMERATE_SHELL_OPTION
+
 private:
     Shell();
     virtual ~Shell() override;