remove newline escaping for comments, which is only valid as a side e…

…ffect of CPP

grammar/import.js

@@ -18,10 +18,7 @@ module.exports = {
     $.variable,
     seq(
       optional($.namespace),
-      choice(
-        $._tyconid,
-        $._sym_prefix,
-      ),
+      choice($._tyconid, $._sym_prefix),
       optional($.import_con_names),
     ),
   ),

src/scanner.c

@@ -1419,15 +1419,30 @@ static bool seq(Env *env, const char *restrict s) {
 }
 
 /**
- * Advance until the next newline or EOF, used to consume the body of a cpp directive or comment.
- * Escaped newlines are treated as line continuations.
+ * Advance until the next newline or EOF, used to consume the body of a comment.
  */
 static void take_line(Env *env) {
+  while (not_eof(env) && !is_newline(PEEK)) S_ADVANCE;
+}
+
+static bool is_space_or_tab(int32_t c) {
+  return c == ' ' || c == '\t';
+}
+
+/**
+ * Advance until the next newline or EOF, used to consume the body of a cpp directive.
+ * Escaped newlines are treated as line continuations, which allow spaces and tabs between backslash and newline.
+ */
+static void take_line_escaped_newline(Env *env) {
   for (;;) {
     while (not_eof(env) && !is_newline(PEEK) && PEEK != '\\') S_ADVANCE;
     if (PEEK == '\\') {
       S_ADVANCE;
-      S_ADVANCE;
+      if (is_space_or_tab(PEEK)) {
+        while (is_space_or_tab(PEEK)) S_ADVANCE;
+        if (is_newline(PEEK)) S_ADVANCE;
+      }
+      else S_ADVANCE;
     }
     else return;
   }
@@ -2374,7 +2389,7 @@ static Lexed lex(Env *env, bool bol) {
 static Symbol cpp_else(Env *env, bool emit) {
   uint32_t nesting = 1;
   do {
-    take_line(env);
+    take_line_escaped_newline(env);
     if (emit) MARK("cpp_else");
     S_ADVANCE;
     reset_lookahead(env);
@@ -2395,7 +2410,7 @@ static Symbol cpp_else(Env *env, bool emit) {
 }
 
 static Symbol cpp_line(Env *env) {
-  take_line(env);
+  take_line_escaped_newline(env);
   return finish_marked(env, CPP, "cpp");
 }
 
@@ -2869,10 +2884,10 @@ static void newline_lookahead(Env *env) {
             break;
           case LCppElse:
             cpp_else(env, false);
-            take_line(env);
+            take_line_escaped_newline(env);
             break;
           case LCpp:
-            take_line(env);
+            take_line_escaped_newline(env);
             break;
           default:
             return;

test/corpus/comment.txt

@@ -221,25 +221,6 @@ a = a
         (variable)))
     (comment)))
 
-================================================================================
-comment: escaped newline
-================================================================================
-
-a = a
-
--- a \
-a = a
-
---------------------------------------------------------------------------------
-
-(haskell
-  (declarations
-    (bind
-      (variable)
-      (exp_name
-        (variable)))
-    (comment)))
-
 ================================================================================
 comment: haddock
 ================================================================================

test/corpus/cpp.txt

@@ -638,3 +638,25 @@ a = do
         (exp_statement
           (exp_name
             (variable)))))))
+
+================================================================================
+cpp: newline continuation
+================================================================================
+
+#if \
+1
+#endif
+
+-- this one has trailing whitespace, which is valid
+#if \ 	  
+1
+#endif
+
+--------------------------------------------------------------------------------
+
+(haskell
+  (cpp)
+  (cpp)
+  (comment)
+  (cpp)
+  (cpp))