Reject char literal of raw newline

Don't allow char literal to span a natural line
ending, but do allow `'\u000A'` to mean `'\n'`.
The spec was updated to reflect that meaning,
and the direction is to eliminate Unicode escapes
outside quotes.

Update the test rig so that `// nopos-error` can
count as `// anypos-error` since the test cannot
be expressed on one line with a trailing comment.

Author: som-snytt

compiler/src/dotty/tools/dotc/parsing/Scanners.scala

@@ -773,19 +773,25 @@ object Scanners {
             }
           fetchDoubleQuote()
         case '\'' =>
-          def fetchSingleQuote() = {
+          def fetchSingleQuote(): Unit = {
             nextChar()
-            if (isIdentifierStart(ch))
+            if isIdentifierStart(ch) then
               charLitOr { getIdentRest(); QUOTEID }
-            else if (isOperatorPart(ch) && (ch != '\\'))
+            else if isOperatorPart(ch) && ch != '\\' then
               charLitOr { getOperatorRest(); QUOTEID }
             else ch match {
               case '{' | '[' | ' ' | '\t' if lookaheadChar() != '\'' =>
                 token = QUOTE
-              case _ =>
+              case _ if !isAtEnd && (ch != SU && ch != CR && ch != LF || isUnicodeEscape) =>
+                val isEmptyCharLit = (ch == '\'')
                 getLitChar()
-                if (ch == '\'') finishCharLit()
+                if ch == '\'' then
+                  if isEmptyCharLit then error("empty character literal (use '\\'' for single quote)")
+                  else finishCharLit()
+                else if isEmptyCharLit then error("empty character literal")
                 else error("unclosed character literal")
+              case _ =>
+                error("unclosed character literal")
             }
           }
           fetchSingleQuote()

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -694,15 +694,21 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
       val errors = errorMap.get(key)
 
+      def missing = { echo(s"Error reported in ${pos1.source}, but no annotation found") ; false }
+
       if (errors ne null) {
         if (errors == 1) errorMap.remove(key)
         else errorMap.put(key, errors - 1)
         true
       }
-      else {
-        echo(s"Error reported in ${pos1.source}, but no annotation found")
-        false
-      }
+      else if key == "nopos" then
+        missing
+      else
+        errorMap.get("nopos") match
+          case null  => missing
+          case 1     => errorMap.remove("nopos") ; true
+          case slack => if slack < 1 then missing
+                        else errorMap.put("nopos", slack - 1) ; true
     }
   }
 

tests/neg/t6810.check

@@ -0,0 +1,24 @@
+-- Error: tests/neg/t6810.scala:5:10 -----------------------------------------------------------------------------------
+5 |  val y = '
+  |          ^
+  |          unclosed character literal
+-- Error: tests/neg/t6810.scala:12:10 ----------------------------------------------------------------------------------
+12 |  val Y = "
+   |          ^
+   |          unclosed string literal
+-- Error: tests/neg/t6810.scala:13:0 -----------------------------------------------------------------------------------
+13 |"                     // error obviously not
+   |^
+   |unclosed string literal
+-- Error: tests/neg/t6810.scala:24:6 -----------------------------------------------------------------------------------
+24 |  val `
+   |      ^
+   |      unclosed quoted identifier
+-- Error: tests/neg/t6810.scala:25:0 -----------------------------------------------------------------------------------
+25 |` = EOL               // error not raw string literals aka triple-quoted, multiline strings
+   |^
+   |unclosed quoted identifier
+-- Error: tests/neg/t6810.scala:30:10 ----------------------------------------------------------------------------------
+30 |  val b = '
+   |          ^
+   |          unclosed character literal

tests/neg/t6810.scala

@@ -0,0 +1,33 @@
+
+trait t6810 {
+  val x = '\u000A'    // char literals accept arbitrary unicode escapes
+                      // nopos-error so as not to interfere with the following bad syntax
+  val y = '
+'                     // but not embedded EOL sequences not represented as escapes
+  println();          // scanner firewall
+  val z = '\n'        // normally, expect this escape
+
+  val X = "\u000A"    // it's the same as ordinary string literals
+                      // nopos-error so as not to interfere with the following bad syntax
+  val Y = "
+"                     // error obviously not
+  val Z = "\n"        // normally, expect this escape
+
+  val A = """
+"""                   // which is what these are for
+  val B = s"""
+"""                   // or the same for interpolated strings
+
+  import System.{lineSeparator => EOL}
+  val `\u000A` = EOL  // backquoted identifiers are arbitrary string literals
+                      // nopos-error so as not to interfere with the following bad syntax
+  val `
+` = EOL               // error not raw string literals aka triple-quoted, multiline strings
+
+  val firebreak = 42  // help parser recovery, could also use rbrace
+
+  val a = '\u000D'    // similar treatment of CR
+  val b = ''        // nopos-error CR seen as EOL by scanner; FSR, error only on open quote, unlike `y`
+  println();          // scanner firewall
+  val c = '\r'        // traditionally
+}