3233 - change how Mu escapes strings

Thanks Sam Putman for helping think through this idea.

When you encounter a backslash, strip it out and pass through any
following run of backslashes. If we 'escaped' a single following
character like C, then the character '\' would be the same as:

  '\\' escaped once
  '\\\\' escaped twice
  '\\\\\\\\' escaped thrice (8 backslashes)

..and so on, the number of backslashes doubling each time. Instead, our
approach is to make the character '\' the same as:

  '\\' escaped once
  '\\\' escaped twice
  '\\\\' escaped thrice

..and so on, the number of backslashes merely increasing by one each
time.

This approach only works as long as backslashes aren't also overloaded
to create special characters. So Mu doesn't follow C's approach of
overloading backslashes both to escape quote characters and also as a
notation for unprintable characters like '\n'.

1 files changed, 26 insertions, 4 deletions

diff --git a/014literal_string.cc b/014literal_string.cc
index 421e873f..ec6a859f 100644
--- a/014literal_string.cc
+++ b/014literal_string.cc
@@ -64,7 +64,7 @@ void slurp_quoted_comment_oblivious(istream& in, ostream& out) {
   while (has_data(in)) {
     char c = in.get();
     if (c == '\\') {
-      out << static_cast<char>(in.get());
+      slurp_one_past_backslashes(in, out);
       continue;
     }
     out << c;
@@ -83,7 +83,7 @@ void slurp_quoted_comment_aware(istream& in, ostream& out) {
   char c;
   while (in >> c) {
     if (c == '\\') {
-      out << static_cast<char>(in.get());
+      slurp_one_past_backslashes(in, out);
       continue;
     }
     if (c == '#') {
@@ -145,6 +145,28 @@ void strip_last(string& s) {
   if (!s.empty()) s.erase(SIZE(s)-1);
 }
 
+void slurp_one_past_backslashes(istream& in, ostream& out) {
+  // When you encounter a backslash, strip it out and pass through any
+  // following run of backslashes. If we 'escaped' a single following
+  // character, then the character '\' would be:
+  //   '\\' escaped once
+  //   '\\\\' escaped twice
+  //   '\\\\\\\\' escaped thrice (8 backslashes)
+  // ..and so on. With our approach it'll be:
+  //   '\\' escaped once
+  //   '\\\' escaped twice
+  //   '\\\\' escaped thrice
+  // This only works as long as backslashes aren't also overloaded to create
+  // special characters. So Mu doesn't follow C's approach of overloading
+  // backslashes both to escape quote characters and also as a notation for
+  // unprintable characters like '\n'.
+  while (has_data(in)) {
+    char c = in.get();
+    out << c;
+    if (c != '\\') break;
+  }
+}
+
 :(scenario string_literal_nested)
 def main [
   1:address:array:character <- copy [abc [def]]
@@ -157,10 +179,10 @@ def main [
 ]
 +parse:   ingredient: {"abc [def": "literal-string"}
 
-:(scenario string_literal_escaped_comment_aware)
+:(scenario string_literal_escaped_twice)
 def main [
   1:address:array:character <- copy [
-abc \\\[def]
+abc \\[def]
 ]
 +parse:   ingredient: {"\nabc \[def": "literal-string"}