Split up util.{hh,cc}

All OS and IO operations should be moved out, leaving only some misc
portable pure functions.

This is useful to avoid copious CPP when doing things like Windows and
Emscripten ports.

Newly exposed functions to break cycles:

 - `restoreSignals`
 - `updateWindowSize`

src/libutil/terminal.cc

@@ -0,0 +1,108 @@
+#include "terminal.hh"
+#include "environment-variables.hh"
+#include "sync.hh"
+
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+namespace nix {
+
+bool shouldANSI()
+{
+    return isatty(STDERR_FILENO)
+        && getEnv("TERM").value_or("dumb") != "dumb"
+        && !(getEnv("NO_COLOR").has_value() || getEnv("NOCOLOR").has_value());
+}
+
+std::string filterANSIEscapes(std::string_view s, bool filterAll, unsigned int width)
+{
+    std::string t, e;
+    size_t w = 0;
+    auto i = s.begin();
+
+    while (w < (size_t) width && i != s.end()) {
+
+        if (*i == '\e') {
+            std::string e;
+            e += *i++;
+            char last = 0;
+
+            if (i != s.end() && *i == '[') {
+                e += *i++;
+                // eat parameter bytes
+                while (i != s.end() && *i >= 0x30 && *i <= 0x3f) e += *i++;
+                // eat intermediate bytes
+                while (i != s.end() && *i >= 0x20 && *i <= 0x2f) e += *i++;
+                // eat final byte
+                if (i != s.end() && *i >= 0x40 && *i <= 0x7e) e += last = *i++;
+            } else {
+                if (i != s.end() && *i >= 0x40 && *i <= 0x5f) e += *i++;
+            }
+
+            if (!filterAll && last == 'm')
+                t += e;
+        }
+
+        else if (*i == '\t') {
+            i++; t += ' '; w++;
+            while (w < (size_t) width && w % 8) {
+                t += ' '; w++;
+            }
+        }
+
+        else if (*i == '\r' || *i == '\a')
+            // do nothing for now
+            i++;
+
+        else {
+            w++;
+            // Copy one UTF-8 character.
+            if ((*i & 0xe0) == 0xc0) {
+                t += *i++;
+                if (i != s.end() && ((*i & 0xc0) == 0x80)) t += *i++;
+            } else if ((*i & 0xf0) == 0xe0) {
+                t += *i++;
+                if (i != s.end() && ((*i & 0xc0) == 0x80)) {
+                    t += *i++;
+                    if (i != s.end() && ((*i & 0xc0) == 0x80)) t += *i++;
+                }
+            } else if ((*i & 0xf8) == 0xf0) {
+                t += *i++;
+                if (i != s.end() && ((*i & 0xc0) == 0x80)) {
+                    t += *i++;
+                    if (i != s.end() && ((*i & 0xc0) == 0x80)) {
+                        t += *i++;
+                        if (i != s.end() && ((*i & 0xc0) == 0x80)) t += *i++;
+                    }
+                }
+            } else
+                t += *i++;
+        }
+    }
+
+    return t;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+static Sync<std::pair<unsigned short, unsigned short>> windowSize{{0, 0}};
+
+
+void updateWindowSize()
+{
+    struct winsize ws;
+    if (ioctl(2, TIOCGWINSZ, &ws) == 0) {
+        auto windowSize_(windowSize.lock());
+        windowSize_->first = ws.ws_row;
+        windowSize_->second = ws.ws_col;
+    }
+}
+
+
+std::pair<unsigned short, unsigned short> getWindowSize()
+{
+    return *windowSize.lock();
+}
+
+}