clang-format: [JS] support null operators.

Summary:
JavaScript / TypeScript is adding two new operators: the null
propagating operator `?.` and the nullish coalescing operator `??`.

    const x = foo ?? 'default';
    const z = foo?.bar?.baz;

This change adds support to lex and format both.

Reviewers: krasimir

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69971

1 files changed, 12 insertions, 0 deletions

diff --git a/clang/lib/Format/FormatTokenLexer.cpp b/clang/lib/Format/FormatTokenLexer.cpp
index 5d8a77577c0..ef20ba884fb 100644
--- a/clang/lib/Format/FormatTokenLexer.cpp
+++ b/clang/lib/Format/FormatTokenLexer.cpp
@@ -100,6 +100,10 @@ void FormatTokenLexer::tryMergePreviousTokens() {
     static const tok::TokenKind JSExponentiation[] = {tok::star, tok::star};
     static const tok::TokenKind JSExponentiationEqual[] = {tok::star,
                                                            tok::starequal};
+    static const tok::TokenKind JSNullPropagatingOperator[] = {tok::question,
+                                                               tok::period};
+    static const tok::TokenKind JSNullishOperator[] = {tok::question,
+                                                       tok::question};
 
     // FIXME: Investigate what token type gives the correct operator priority.
     if (tryMergeTokens(JSIdentity, TT_BinaryOperator))
@@ -116,6 +120,14 @@ void FormatTokenLexer::tryMergePreviousTokens() {
       Tokens.back()->Tok.setKind(tok::starequal);
       return;
     }
+    if (tryMergeTokens(JSNullishOperator, TT_JsNullishCoalescingOperator))
+      return;
+    if (tryMergeTokens(JSNullPropagatingOperator,
+                       TT_JsNullPropagatingOperator)) {
+      // Treat like a regular "." access.
+      Tokens.back()->Tok.setKind(tok::period);
+      return;
+    }
     if (tryMergeJSPrivateIdentifier())
       return;
   }