clang-format: handle formatting on constexpr if

[thegameg]

Summary

c++1z adds the following constructions to the language:

if constexpr (cond)
  statement1;
else if constexpr (cond)
  statement2;
else if constexpr (cond)
  statement3;
else
  statement4;

so clang-format needs to accept the constexpr keyword after the if
keyword.

• lib/Format/TokenAnnotator.cpp: Handle Style.SpaceBeforeParens.
• lib/Format/UnwrappedLineParser.cpp: Skip the token when parsing

ifThenElse.

• unittests/Format/FormatTest.cpp: Tests.

[outcoldman]

The actual problem is with that clang-format does not know anything about c++17 features, because it does not set it in lang options. Not sure if that will fix constexpr problem as well, but I could solve some other problems with

tools/clang                                                                                                                        ✓  13:45:12 
╰─ svn diff
Index: lib/Format/Format.cpp
===================================================================
--- lib/Format/Format.cpp	(revision 297506)
+++ lib/Format/Format.cpp	(working copy)
@@ -1893,6 +1893,7 @@
   LangOpts.CPlusPlus = 1;
   LangOpts.CPlusPlus11 = Style.Standard == FormatStyle::LS_Cpp03 ? 0 : 1;
   LangOpts.CPlusPlus14 = Style.Standard == FormatStyle::LS_Cpp03 ? 0 : 1;
+  LangOpts.CPlusPlus1z = Style.Standard == FormatStyle::LS_Cpp03 ? 0 : 1;
   LangOpts.LineComment = 1;
   bool AlternativeOperators = Style.IsCpp();
   LangOpts.CXXOperatorNames = AlternativeOperators ? 1 : 0;

[• gnzlbg]

any progress on this?

[outcoldman]

In D26953#716504, @gnzlbg wrote:

any progress on this?

It is getting tracked in mailing list http://lists.llvm.org/pipermail/cfe-dev/2017-April/053397.html

[thakis]

This looks good to me, thanks. Sorry about the slow turnaround. Do you have commit access? If not, I can land it for you – but it also looks like you've contributed several patches by now, so you could also ask for commit access if you don't have it yet.

[thegameg]

In D26953#751021, @thakis wrote:

This looks good to me, thanks. Sorry about the slow turnaround. Do you have commit access? If not, I can land it for you – but it also looks like you've contributed several patches by now, so you could also ask for commit access if you don't have it yet.

Thank you for the review. As @gnzlbg pointed out here (PR28867), I tested with AllowShortIfStatementsOnASingleLine and it does not seem to work as intended. I didn't have time to fix that yet, so I'll probably delay this for now. If anyone has time, feel free to fix + land this instead of me.

[jtbandes]

Hm, I probably should've searched first — but I just re-implemented this in D34330. Actually, I think my implementation solves the AllowShortIfStatementsOnASingleLine issue you were mentioning here 🎉

[djasper]

Submitted the other implementation of this as r305666.

[thegameg]

In D26953#783497, @jtbandes wrote:

Hm, I probably should've searched first — but I just re-implemented this in D34330. Actually, I think my implementation solves the AllowShortIfStatementsOnASingleLine issue you were mentioning here 🎉

No problem! Great!

lib/Format/TokenAnnotator.cpp

       return true;
     return Line.Type == LT_ObjCDecl || Left.is(tok::semi) ||
            (Style.SpaceBeforeParens != FormatStyle::SBPO_Never &&
-            (Left.isOneOf(tok::kw_if, tok::pp_elif, tok::kw_for, tok::kw_while,
-                          tok::kw_switch, tok::kw_case, TT_ForEachMacro,
-                          TT_ObjCForIn) ||
+            (Left.isOneOf(tok::kw_if, tok::kw_constexpr, tok::pp_elif,
+                          tok::kw_for, tok::kw_while, tok::kw_switch,
+                          tok::kw_case, TT_ForEachMacro, TT_ObjCForIn) ||
              (Left.isOneOf(tok::kw_try, Keywords.kw___except, tok::kw_catch,
                            tok::kw_new, tok::kw_delete) &&
               (!Left.Previous || Left.Previous->isNot(tok::period))))) ||

lib/Format/UnwrappedLineParser.cpp

 void UnwrappedLineParser::parseIfThenElse() {
   assert(FormatTok->Tok.is(tok::kw_if) && "'if' expected");
   nextToken();
+  if (FormatTok->Tok.is(tok::kw_constexpr))
+    nextToken();
   if (FormatTok->Tok.is(tok::l_paren))
     parseParens();
   bool NeedsUnwrappedLine = false;

unittests/Format/FormatTest.cpp

                    "/* comment 3 */         \\\n",
                    getLLVMStyleWithColumns(40)));
 }
+
+TEST_F(FormatTest, ConstexprIf) {
+  EXPECT_EQ("if constexpr (3 > 4)",
+            format("if constexpr(3 > 4)",
+                   getLLVMStyle()));
+  EXPECT_EQ("if constexpr (3 > 4)",
+            format("if \n"
+                   "  constexpr(3 > 4)",
+                   getLLVMStyle()));
+}
+
 } // end namespace
 } // end namespace format
 } // end namespace clang