2 files changed, 24 insertions, 0 deletions
diff --git a/cpp/tangle/030tangle.cc b/cpp/tangle/030tangle.cc
index adbf925b..896e8f3e 100644
--- a/cpp/tangle/030tangle.cc
+++ b/cpp/tangle/030tangle.cc
@@ -1,3 +1,7 @@
+// Reorder a file based on directives starting with ':(' (tangle directives).
+// Insert #line directives to preserve line numbers in the original.
+// Clear lines starting with '//:' (tangle comments).
+
 #include<assert.h>
 #include<sys/param.h>
 
@@ -28,6 +32,10 @@ void tangle(istream& in, list<string>& out) {
     else
       out.push_back(curr_line);
   }
+  for (list<string>::iterator p = out.begin(); p != out.end(); ++p) {
+    if (starts_with(*p, "//:"))
+      p->clear();  // leave the empty lines around so as to not mess up #line numbers
+  }
   trace_all("tangle", out);
 }
 
diff --git a/cpp/tangle/030tangle.test.cc b/cpp/tangle/030tangle.test.cc
index 4aab6316..3f86fdb8 100644
--- a/cpp/tangle/030tangle.test.cc
+++ b/cpp/tangle/030tangle.test.cc
@@ -48,6 +48,22 @@ void test_tangle_with_multiple_filenames_after() {
 //?   exit(0); //? 1
 }
 
+void test_tangle_skip_tanglecomments() {
+  istringstream in("a\nb\nc\n//: 1\n//: 2\nd\n");
+  list<string> dummy;
+  tangle(in, dummy);
+  CHECK_TRACE_CONTENTS("tangle", "abcd");
+  CHECK_TRACE_DOESNT_CONTAIN("tangle", "//: 1");
+}
+
+void test_tangle_with_tanglecomments_and_directive() {
+  istringstream in("a\n//: 1\nb\nc\n:(before b)\nd\n:(code)\ne\n");
+  list<string> dummy;
+  tangle(in, dummy);
+  CHECK_TRACE_CONTENTS("tangle", "a#line 6d#line 3bc#line 8e");
+  CHECK_TRACE_DOESNT_CONTAIN("tangle", "//: 1");
+}
+
 void test_tangle2() {
   istringstream in("a\nb\nc\n:(after b)\nd\n");
   list<string> dummy;