From: Nico Weber <nicolasweber@gmx.de>
Date: Fri, 13 Sep 2019 13:18:55 +0000 (+0000)
Subject: clang-format: Add support for formatting (some) lambdas with explicit template parame... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e7ad04375483f262116f29730feaa0e2b4af4e47;p=clang

clang-format: Add support for formatting (some) lambdas with explicit template parameters.

This patch makes cases work where the lambda's template list doesn't
contain any of + - ! ~ / % << | || && ^ == != >= <= ? : true false
(see added FIXME).

Ports r359967 to clang-format.

Differential Revision: https://reviews.llvm.org/D67246

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@371854 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Format/TokenAnnotator.cpp b/lib/Format/TokenAnnotator.cpp
index 55ab654f96..9802711834 100644
--- a/lib/Format/TokenAnnotator.cpp
+++ b/lib/Format/TokenAnnotator.cpp
@@ -40,6 +40,21 @@ static bool canBeObjCSelectorComponent(const FormatToken &Tok) {
   return Tok.Tok.getIdentifierInfo() != nullptr;
 }
 
+/// With `Left` being '(', check if we're at either `[...](` or
+/// `[...]<...>(`, where the [ opens a lambda capture list.
+static bool isLambdaParameterList(const FormatToken *Left) {
+  // Skip <...> if present.
+  if (Left->Previous && Left->Previous->is(tok::greater) &&
+      Left->Previous->MatchingParen &&
+      Left->Previous->MatchingParen->is(TT_TemplateOpener))
+    Left = Left->Previous->MatchingParen;
+
+  // Check for `[...]`.
+  return Left->Previous && Left->Previous->is(tok::r_square) &&
+         Left->Previous->MatchingParen &&
+         Left->Previous->MatchingParen->is(TT_LambdaLSquare);
+}
+
 /// A parser that gathers additional information about tokens.
 ///
 /// The \c TokenAnnotator tries to match parenthesis and square brakets and
@@ -191,9 +206,7 @@ private:
                Left->Previous->is(TT_JsTypeColon)) {
       // let x: (SomeType);
       Contexts.back().IsExpression = false;
-    } else if (Left->Previous && Left->Previous->is(tok::r_square) &&
-               Left->Previous->MatchingParen &&
-               Left->Previous->MatchingParen->is(TT_LambdaLSquare)) {
+    } else if (isLambdaParameterList(Left)) {
       // This is a parameter list of a lambda expression.
       Contexts.back().IsExpression = false;
     } else if (Line.InPPDirective &&
diff --git a/lib/Format/UnwrappedLineParser.cpp b/lib/Format/UnwrappedLineParser.cpp
index e552a055b0..8fd0e9433b 100644
--- a/lib/Format/UnwrappedLineParser.cpp
+++ b/lib/Format/UnwrappedLineParser.cpp
@@ -1440,8 +1440,11 @@ bool UnwrappedLineParser::tryToParseLambda() {
     case tok::identifier:
     case tok::numeric_constant:
     case tok::coloncolon:
+    case tok::kw_class:
     case tok::kw_mutable:
     case tok::kw_noexcept:
+    case tok::kw_template:
+    case tok::kw_typename:
       nextToken();
       break;
     // Specialization of a template with an integer parameter can contain
@@ -1455,6 +1458,9 @@ bool UnwrappedLineParser::tryToParseLambda() {
     // followed by an `a->b` expression, such as:
     // ([obj func:arg] + a->b)
     // Otherwise the code below would parse as a lambda.
+    //
+    // FIXME: This heuristic is incorrect for C++20 generic lambdas with
+    // explicit template lists: []<bool b = true && false>(U &&u){}
     case tok::plus:
     case tok::minus:
     case tok::exclaim:
diff --git a/unittests/Format/FormatTest.cpp b/unittests/Format/FormatTest.cpp
index f1a1160fa1..b1fcd39a49 100644
--- a/unittests/Format/FormatTest.cpp
+++ b/unittests/Format/FormatTest.cpp
@@ -12923,6 +12923,10 @@ TEST_F(FormatTest, FormatsLambdas) {
                "  return 1; //\n"
                "};");
 
+  // Lambdas with explicit template argument lists.
+  verifyFormat(
+      "auto L = []<template <typename> class T, class U>(T<U> &&a) {};\n");
+
   // Multiple lambdas in the same parentheses change indentation rules. These
   // lambdas are forced to start on new lines.
   verifyFormat("SomeFunction(\n"
@@ -12940,8 +12944,8 @@ TEST_F(FormatTest, FormatsLambdas) {
                "    },\n"
                "    1);\n");
 
-  // A multi-line lambda passed as arg1 forces arg0 to be pushed out, just like the arg0
-  // case above.
+  // A multi-line lambda passed as arg1 forces arg0 to be pushed out, just like
+  // the arg0 case above.
   auto Style = getGoogleStyle();
   Style.BinPackArguments = false;
   verifyFormat("SomeFunction(\n"