Add smartcase to the regex engine.

doc/pages/regex.asciidoc

@@ -167,6 +167,7 @@ them:
 * `(?I)` starts case-sensitive matching (default).
 * `(?s)` allows `.` to match newlines (default).
 * `(?S)` prevents `.` from matching newlines.
+* `(?c)` enable smartcase, starts case-insensitive matching unless an uppercase character is present in the pattern.
 
 == Quoting
 

src/regex_impl.cc

@@ -153,6 +153,7 @@ struct RegexParser
         None              = 0,
         IgnoreCase        = 1 << 0,
         DotMatchesNewLine = 1 << 1,
+        SmartCase         = 1 << 2,
     };
     friend constexpr bool with_bit_ops(Meta::Type<Flags>) { return true; }
 
@@ -212,6 +213,7 @@ struct RegexParser
                     case 'I': m_flags &= ~Flags::IgnoreCase; break;
                     case 's': m_flags |= Flags::DotMatchesNewLine; break;
                     case 'S': m_flags &= ~Flags::DotMatchesNewLine; break;
+                    case 'c': m_flags |= Flags::SmartCase | Flags::IgnoreCase; break;
                     case ')':
                         m_pos = Iterator{it, m_regex};
                         return true;
@@ -328,6 +330,14 @@ struct RegexParser
                 if (contains(StringView{"^$.*+?[]{}"}, cp) or (cp >= 0xF0000 and cp <= 0xFFFFF))
                     parse_error(format("unexpected '{}'", cp));
                 ++m_pos;
+                if (is_upper(cp) && (m_flags & Flags::SmartCase)) {
+                    m_flags &= ~Flags::IgnoreCase;
+                    for (ParsedRegex::Node &node : m_parsed_regex.nodes)
+                        node.ignore_case = false;
+                    for (CharacterClass &char_class : m_parsed_regex.character_classes)
+                        char_class.ignore_case = false;
+
+                }
                 return add_node(ParsedRegex::Literal, cp);
         }
     }

test/normal/search-character-class/cmd

@@ -0,0 +1 @@
+/(?c)[a-z]ooBar<ret>

test/normal/search-character-class/in

@@ -0,0 +1 @@
+%(f)oobar FooBar fooBar

test/normal/search-character-class/kak_quoted_selections

@@ -0,0 +1 @@
+'fooBar'

test/normal/search-smartcase/cmd

@@ -0,0 +1 @@
+/fooBar<ret>

test/normal/search-smartcase/in

@@ -0,0 +1 @@
+%(f)oobar FooBar fooBar

test/normal/search-smartcase/kak_quoted_selections

@@ -0,0 +1 @@
+'fooBar'