Improved logging abstraction

This also gets rid of --log-type, since the nested log type isn't
useful in a multi-threaded situation, and nobody cares about the
"pretty" log type.

src/libutil/logging.cc

@@ -0,0 +1,79 @@
+#include "logging.hh"
+#include "util.hh"
+
+namespace nix {
+
+Logger * logger = 0;
+
+class SimpleLogger : public Logger
+{
+public:
+
+    bool systemd, tty;
+
+    SimpleLogger()
+    {
+        systemd = getEnv("IN_SYSTEMD") == "1";
+        tty = isatty(STDERR_FILENO);
+    }
+
+    void log(Verbosity lvl, const FormatOrString & fs) override
+    {
+        if (lvl > verbosity) return;
+
+        std::string prefix;
+
+        if (systemd) {
+            char c;
+            switch (lvl) {
+            case lvlError: c = '3'; break;
+            case lvlInfo: c = '5'; break;
+            case lvlTalkative: case lvlChatty: c = '6'; break;
+            default: c = '7';
+            }
+            prefix = std::string("<") + c + ">";
+        }
+
+        writeToStderr(prefix + (tty ? fs.s : filterANSIEscapes(fs.s)) + "\n");
+    }
+
+    void startActivity(Activity & activity, Verbosity lvl, const FormatOrString & fs) override
+    {
+        log(lvl, fs);
+    }
+
+    void stopActivity(Activity & activity) override
+    {
+    }
+};
+
+Verbosity verbosity = lvlInfo;
+
+void warnOnce(bool & haveWarned, const FormatOrString & fs)
+{
+    if (!haveWarned) {
+        printMsg(lvlError, format("warning: %1%") % fs.s);
+        haveWarned = true;
+    }
+}
+
+void writeToStderr(const string & s)
+{
+    try {
+        writeFull(STDERR_FILENO, s);
+    } catch (SysError & e) {
+        /* Ignore failing writes to stderr if we're in an exception
+           handler, otherwise throw an exception.  We need to ignore
+           write errors in exception handlers to ensure that cleanup
+           code runs to completion if the other side of stderr has
+           been closed unexpectedly. */
+        if (!std::uncaught_exception()) throw;
+    }
+}
+
+Logger * makeDefaultLogger()
+{
+    return new SimpleLogger();
+}
+
+}