Fix parsing of nested classes with private fields

The parsing of private fields checks whether or not it is within a
class to determine if it is valid or not. However, the state.inClass
property is incorrect as it marks it as outside a class when the inner
class is closed.

This commit fixes this problem by replacing the state.inClass property
with a class nesting counter.

src/parser/statement.js

@@ -684,7 +684,7 @@ export default class StatementParser extends ExpressionParser {
     // class bodies are implicitly strict
     const oldStrict = this.state.strict;
     this.state.strict = true;
-    this.state.inClass = true;
+    this.state.classLevel++;
 
     const state = { hadConstructor: false };
     let decorators = [];
@@ -731,7 +731,7 @@ export default class StatementParser extends ExpressionParser {
 
     node.body = this.finishNode(classBody, "ClassBody");
 
-    this.state.inClass = false;
+    this.state.classLevel--;
     this.state.strict = oldStrict;
   }
 

src/tokenizer/index.js

@@ -444,7 +444,7 @@ export default class Tokenizer extends LocationParser {
     switch (code) {
 
       case 35: // '#'
-        if (this.hasPlugin("classPrivateProperties") && this.state.inClass) {
+        if (this.hasPlugin("classPrivateProperties") && this.state.classLevel > 0) {
           ++this.state.pos; return this.finishToken(tt.hash);
         } else {
           this.raise(this.state.pos, `Unexpected character '${codePointToString(code)}'`);

src/tokenizer/state.js

@@ -24,11 +24,12 @@ export default class State {
       this.inAsync =
       this.inPropertyName =
       this.inType =
-      this.inClass =
       this.inClassProperty =
       this.noAnonFunctionType =
         false;
 
+    this.classLevel = 0;
+
     this.labels = [];
 
     this.decorators = [];
@@ -84,7 +85,9 @@ export default class State {
   noAnonFunctionType: boolean;
   inPropertyName: boolean;
   inClassProperty: boolean;
-  inClass: boolean;
+
+  // Check whether we are in a (nested) class or not.
+  classLevel: number;
 
   // Labels in scope.
   labels: Array<{ kind: ?("loop" | "switch"), statementStart?: number }>;