[clang-format] Add options to AllowShortIfStatementsOnASingleLine to apply to "else if" and "else".

This fixes the bug http://llvm.org/pr50019.

Reviewed By: MyDeveloperDay

Differential Revision: https://reviews.llvm.org/D100727

Author: mkurdej

clang/docs/ReleaseNotes.rst

@@ -1,4 +1,4 @@
-========================================
+q========================================
 Clang 13.0.0 (In-Progress) Release Notes
 ========================================
 
@@ -239,6 +239,10 @@ clang-format
 - Option ``SpacesInAngles`` has been improved, it now accepts ``Leave`` value
   that allows to keep spaces where they are already present.
 
+- Option ``AllowShortIfStatementsOnASingleLine`` has been improved, it now
+  accepts ``AllIfsAndElse`` value that allows to put "else if" and "else" short
+  statements on a single line. (Fixes https://llvm.org/PR50019.)
+
 libclang
 --------
 

clang/include/clang/Format/Format.h

@@ -620,37 +620,74 @@ struct FormatStyle {
   /// single line.
   ShortFunctionStyle AllowShortFunctionsOnASingleLine;
 
-  /// Different styles for handling short if lines
+  /// Different styles for handling short if statements.
   enum ShortIfStyle : unsigned char {
     /// Never put short ifs on the same line.
     /// \code
     ///   if (a)
-    ///     return ;
+    ///     return;
+    ///
+    ///   if (b)
+    ///     return;
+    ///   else
+    ///     return;
+    ///
+    ///   if (c)
+    ///     return;
     ///   else {
     ///     return;
     ///   }
     /// \endcode
     SIS_Never,
-    /// Without else put short ifs on the same line only if
-    /// the else is not a compound statement.
+    /// Put short ifs on the same line only if there is no else statement.
     /// \code
     ///   if (a) return;
+    ///
+    ///   if (b)
+    ///     return;
     ///   else
     ///     return;
+    ///
+    ///   if (c)
+    ///     return;
+    ///   else {
+    ///     return;
+    ///   }
     /// \endcode
     SIS_WithoutElse,
-    /// Always put short ifs on the same line if
-    /// the else is not a compound statement or not.
+    /// Put short ifs, but not else ifs nor else statements, on the same line.
     /// \code
     ///   if (a) return;
+    ///
+    ///   if (b) return;
+    ///   else if (b)
+    ///     return;
+    ///   else
+    ///     return;
+    ///
+    ///   if (c) return;
+    ///   else {
+    ///     return;
+    ///   }
+    /// \endcode
+    SIS_OnlyFirstIf,
+    /// Always put short ifs, else ifs and else statements on the same
+    /// line.
+    /// \code
+    ///   if (a) return;
+    ///
+    ///   if (b) return;
+    ///   else return;
+    ///
+    ///   if (c) return;
     ///   else {
     ///     return;
     ///   }
     /// \endcode
-    SIS_Always,
+    SIS_AllIfsAndElse,
   };
 
-  /// If ``true``, ``if (a) return;`` can be put on a single line.
+  /// Dependent on the value, ``if (a) return;`` can be put on a single line.
   ShortIfStyle AllowShortIfStatementsOnASingleLine;
 
   /// Different styles for merging short lambdas containing at most one

clang/lib/Format/Format.cpp

@@ -146,10 +146,12 @@ template <> struct ScalarEnumerationTraits<FormatStyle::AlignConsecutiveStyle> {
 template <> struct ScalarEnumerationTraits<FormatStyle::ShortIfStyle> {
   static void enumeration(IO &IO, FormatStyle::ShortIfStyle &Value) {
     IO.enumCase(Value, "Never", FormatStyle::SIS_Never);
-    IO.enumCase(Value, "Always", FormatStyle::SIS_Always);
     IO.enumCase(Value, "WithoutElse", FormatStyle::SIS_WithoutElse);
+    IO.enumCase(Value, "OnlyFirstIf", FormatStyle::SIS_OnlyFirstIf);
+    IO.enumCase(Value, "AllIfsAndElse", FormatStyle::SIS_AllIfsAndElse);
 
     // For backward compatibility.
+    IO.enumCase(Value, "Always", FormatStyle::SIS_OnlyFirstIf);
     IO.enumCase(Value, "false", FormatStyle::SIS_Never);
     IO.enumCase(Value, "true", FormatStyle::SIS_WithoutElse);
   }

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -421,7 +421,16 @@ class LineJoiner {
       }
       return MergedLines;
     }
-    if (TheLine->First->is(tok::kw_if)) {
+    auto IsElseLine = [&First = TheLine->First]() -> bool {
+      if (First->is(tok::kw_else))
+        return true;
+
+      return First->is(tok::r_brace) && First->Next &&
+             First->Next->is(tok::kw_else);
+    };
+    if (TheLine->First->is(tok::kw_if) ||
+        (IsElseLine() && (Style.AllowShortIfStatementsOnASingleLine ==
+                          FormatStyle::SIS_AllIfsAndElse))) {
       return Style.AllowShortIfStatementsOnASingleLine
                  ? tryMergeSimpleControlStatement(I, E, Limit)
                  : 0;
@@ -471,7 +480,8 @@ class LineJoiner {
       return 0;
     Limit = limitConsideringMacros(I + 1, E, Limit);
     AnnotatedLine &Line = **I;
-    if (!Line.First->is(tok::kw_do) && Line.Last->isNot(tok::r_paren))
+    if (!Line.First->is(tok::kw_do) && !Line.First->is(tok::kw_else) &&
+        !Line.Last->is(tok::kw_else) && Line.Last->isNot(tok::r_paren))
       return 0;
     // Only merge do while if do is the only statement on the line.
     if (Line.First->is(tok::kw_do) && !Line.Last->is(tok::kw_do))
@@ -482,7 +492,8 @@ class LineJoiner {
                              TT_LineComment))
       return 0;
     // Only inline simple if's (no nested if or else), unless specified
-    if (Style.AllowShortIfStatementsOnASingleLine != FormatStyle::SIS_Always) {
+    if (Style.AllowShortIfStatementsOnASingleLine ==
+        FormatStyle::SIS_WithoutElse) {
       if (I + 2 != E && Line.startsWith(tok::kw_if) &&
           I[2]->First->is(tok::kw_else))
         return 0;