1 files changed, 37 insertions, 1 deletions
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index aa539a1fa42b..ef0a304dea3b 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2441,6 +2441,42 @@ void DerivationGoal::deleteTmpDir(bool force)
 }
 
 
+/* Filter out the special ANSI escape codes generated by Nixpkgs'
+   stdenv (used to denote nesting etc.). */
+static string filterNixEscapes(const string & s)
+{
+    string t, r;
+    enum { stTop, stEscape, stCSI } state = stTop;
+    for (auto c : s) {
+        if (state == stTop) {
+            if (c == '\e') {
+                state = stEscape;
+                r = c;
+            } else
+                t += c;
+        } else if (state == stEscape) {
+            r += c;
+            if (c == '[')
+                state = stCSI;
+            else {
+                t += r;
+                state = stTop;
+            }
+        } else {
+            r += c;
+            if (c >= 0x40 && c != 0x7e) {
+                if (c != 'p' && c != 'q' && c != 's' && c != 'a' && c != 'b')
+                    t += r;
+                state = stTop;
+                r.clear();
+            }
+        }
+    }
+    t += r;
+    return t;
+}
+
+
 void DerivationGoal::handleChildOutput(int fd, const string & data)
 {
     if ((hook && fd == hook->builderOut.readSide) ||
@@ -2455,7 +2491,7 @@ void DerivationGoal::handleChildOutput(int fd, const string & data)
             return;
         }
         if (verbosity >= settings.buildVerbosity)
-            writeToStderr(data);
+            writeToStderr(filterNixEscapes(data));
         if (bzLogFile) {
             int err;
             BZ2_bzWrite(&err, bzLogFile, (unsigned char *) data.data(), data.size());