Inline Patterns may start with any character. (#150)

`}`, `.`, `*` and `[` are only special when they appear at the beginning of indented Pattern lines. When a Pattern starts on the same line as `id =` or `[variant key]`, its first character doesn't carry any special meaning and it may be one of those four ones as well.

See also https://bugzilla.mozilla.org/show_bug.cgi?id=1436683.

The tests for this uncovered a bug in how the runtime parser treated null attributes and variants. For compliance with fluent-syntax these are syntax errors now.

Author: stasm

fluent-syntax/src/ftlstream.js

@@ -131,22 +131,20 @@ export class FTLParserStream extends ParserStream {
     return isDigit;
   }
 
-  isCharPatternStart(ch) {
+  isCharPatternContinuation(ch) {
     return !includes(SPECIAL_LINE_START_CHARS, ch);
   }
 
   isPeekPatternStart() {
     this.peekInlineWS();
-
     const ch = this.currentPeek();
 
-    if (ch === '\n') {
-      return this.isPeekNextLinePatternStart();
+    // Inline Patterns may start with any char.
+    if (ch !== undefined && ch !== '\n') {
+      return true;
     }
 
-    const isPattern = this.isCharPatternStart(this.currentPeek());
-    this.resetPeek();
-    return isPattern;
+    return this.isPeekNextLinePatternStart();
   }
 
   isPeekNextLineZeroFourStyleComment() {
@@ -276,7 +274,7 @@ export class FTLParserStream extends ParserStream {
       return false;
     }
 
-    if (!this.isCharPatternStart(this.currentPeek())) {
+    if (!this.isCharPatternContinuation(this.currentPeek())) {
       this.resetPeek();
       return false;
     }

fluent-syntax/test/fixtures_structure/leading_dots.ftl

@@ -0,0 +1,64 @@
+key01 = .Value
+key02 = …Value
+key03 = {"."}Value
+key04 =
+    {"."}Value
+
+key05 = Value
+    {"."}Continued
+
+key06 = .Value
+    {"."}Continued
+
+# ERROR (attr .Continued must have a value)
+key07 = Value
+    .Continued
+
+# ERROR (attr .Value must have a value)
+key08 =
+    .Value
+
+# ERROR (attr .Value must have a value)
+key09 =
+    .Value
+    Continued
+
+key10 =
+    .Value = which looks like an attribute
+    Continued
+
+key11 =
+    {"."}Value = which looks like an attribute
+    Continued
+
+key12 =
+    .accesskey =
+    A
+    
+key13 =
+    .attribute = .Value
+
+key14 =
+    .attribute =
+         {"."}Value
+
+key15 =
+    { 1 ->
+        [one] .Value
+       *[other]
+            {"."}Value
+    }
+
+# ERROR (variant must have a value)
+key16 =
+    { 1 ->
+       *[one]
+           .Value
+    }
+
+# ERROR (unclosed placeable)
+key17 =
+    { 1 ->
+       *[one] Value
+           .Continued
+    }