[clang-format] [JS] handle private members.

Addresses PR40999 https://bugs.llvm.org/show_bug.cgi?id=40999

Private fields and methods in JavaScript would get incorrectly indented
(it sees them as preprocessor directives and hence left aligns them)

In this revision `#identifier` tokens `tok::hash->tok::identifier` are
merged into a single new token `tok::identifier` with the `#` contained
inside the TokenText.

Before:

```
class Example {
  pub = 1;

  static pub2 = "foo";
  static #priv2 = "bar";

  method() { this.#priv = 5; }

  static staticMethod() {
    switch (this.#priv) {
    case '1':
      break;
    }
  }

  this.#privateMethod(); // infinite loop
}

static #staticPrivateMethod() {}
}
```

After this fix the code will be correctly indented

```
class Example {
  pub = 1;
  #priv = 2;

  static pub2 = "foo";
  static #priv2 = "bar";

  method() { this.#priv = 5; }

  static staticMethod() {
    switch (this.#priv) {
    case '1':
      #priv = 3;
      break;
    }
  }

  #privateMethod() {
    this.#privateMethod(); // infinite loop
  }

  static #staticPrivateMethod() {}
}
```

NOTE: There might be some JavaScript code out there which uses the C
processor to preprocess .js files
http://www.nongnu.org/espresso/js-cpp.html. It's not clear how this
revision or even private fields and methods would interact.

Patch originally by MyDeveloperDays (thanks!).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356449 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 23 insertions, 0 deletions

diff --git a/lib/Format/FormatToken.h b/lib/Format/FormatToken.h
index 2989c760b6..a5daf8aed4 100644
--- a/lib/Format/FormatToken.h
+++ b/lib/Format/FormatToken.h
@@ -60,6 +60,7 @@ namespace format {
   TYPE(JsExponentiationEqual)                                                  \
   TYPE(JsFatArrow)                                                             \
   TYPE(JsNonNullAssertion)                                                     \
+  TYPE(JsPrivateIdentifier)                                                    \
   TYPE(JsTypeColon)                                                            \
   TYPE(JsTypeOperator)                                                         \
   TYPE(JsTypeOptionalQuestion)                                                 \
diff --git a/lib/Format/FormatTokenLexer.cpp b/lib/Format/FormatTokenLexer.cpp
index 2f1b08a8b0..da755e36c1 100644
--- a/lib/Format/FormatTokenLexer.cpp
+++ b/lib/Format/FormatTokenLexer.cpp
@@ -95,6 +95,8 @@ void FormatTokenLexer::tryMergePreviousTokens() {
       Tokens.back()->Tok.setKind(tok::starequal);
       return;
     }
+    if (tryMergeJSPrivateIdentifier())
+      return;
   }
 
   if (Style.Language == FormatStyle::LK_Java) {
@@ -121,6 +123,25 @@ bool FormatTokenLexer::tryMergeNSStringLiteral() {
   return true;
 }
 
+bool FormatTokenLexer::tryMergeJSPrivateIdentifier() {
+  // Merges #idenfier into a single identifier with the text #identifier
+  // but the token tok::identifier.
+  if (Tokens.size() < 2)
+    return false;
+  auto &Hash = *(Tokens.end() - 2);
+  auto &Identifier = *(Tokens.end() - 1);
+  if (!Hash->is(tok::hash) || !Identifier->is(tok::identifier))
+    return false;
+  Hash->Tok.setKind(tok::identifier);
+  Hash->TokenText =
+      StringRef(Hash->TokenText.begin(),
+                Identifier->TokenText.end() - Hash->TokenText.begin());
+  Hash->ColumnWidth += Identifier->ColumnWidth;
+  Hash->Type = TT_JsPrivateIdentifier;
+  Tokens.erase(Tokens.end() - 1);
+  return true;
+}
+
 bool FormatTokenLexer::tryMergeLessLess() {
   // Merge X,less,less,Y into X,lessless,Y unless X or Y is less.
   if (Tokens.size() < 3)
diff --git a/lib/Format/FormatTokenLexer.h b/lib/Format/FormatTokenLexer.h
index 61a4c041d1..a964626146 100644
--- a/lib/Format/FormatTokenLexer.h
+++ b/lib/Format/FormatTokenLexer.h
@@ -48,6 +48,7 @@ private:
 
   bool tryMergeLessLess();
   bool tryMergeNSStringLiteral();
+  bool tryMergeJSPrivateIdentifier();
 
   bool tryMergeTokens(ArrayRef<tok::TokenKind> Kinds, TokenType NewType);