c++: expand support for c++ float literals (#2123)

* c++: support f, F as float suffixes

Fixes #577

* fix the regex nesting and add visual spec

* add support for hex floats and exps

---------

Co-authored-by: jneen <[email protected]>

Author: jneen

lib/rouge/lexers/cpp.rb

@@ -62,9 +62,10 @@ def self.reserved
         rule %r/(class|struct)\b/, Keyword, :classname
         rule %r/template\b/, Keyword, :template
         rule %r/#{dq}(\.#{dq})?(?:y|d|h|(?:min)|s|(?:ms)|(?:us)|(?:ns)|i|(?:if)|(?:il))\b/, Num::Other
-        rule %r((#{dq}[.]#{dq}?|[.]#{dq})(e[+-]?#{dq}[lu]*)?)i, Num::Float
-        rule %r(#{dq}e[+-]?#{dq}[lu]*)i, Num::Float
-        rule %r/0x\h('?\h)*[lu]*/i, Num::Hex
+        rule %r((#{dq}[.]#{dq}?|[.]#{dq})([ep][+-]?#{dq})?[luf]*)i, Num::Float
+        rule %r(#{dq}[ep][+-]?#{dq}[luf]*)i, Num::Float
+        rule %r/0x\h('?\h)*([ep][+-]?#{dq})?[lu]*/i, Num::Hex
+        rule %r/0x\h('?\h)*[.]\h+([ep][+-]?#{dq})[luf]*/i, Num::Hex
         rule %r/0b[01]+('[01]+)*/, Num::Bin
         rule %r/0[0-7]('?[0-7])*[lu]*/i, Num::Oct
         rule %r/#{dq}[lu]*/i, Num::Integer

spec/visual/samples/cpp

@@ -277,3 +277,44 @@ export struct Shape {
   int m_x;
   int m_y;
 }
+
+float test(8.874L);
+float test(8.874l);
+float test(8.874F);
+float test(8.874f);
+float test(8.874U);
+float test(8.874u);
+
+// via https://en.cppreference.com/w/cpp/language/floating_literal
+int main()
+{
+    std::cout
+        << "Literal" "\t" "Printed value" << std::left
+        << OUT( 58.            ) // double
+        << OUT( 4e2            ) // double
+        << OUT( 123.456e-67    ) // double
+        << OUT( 123.456e-67f   ) // float, truncated to zero
+        << OUT( .1E4f          ) // float
+        << OUT( 0x10.1p0       ) // double
+        << OUT( 0x1p5          ) // double
+        << OUT( 0x1e5          ) // integer literal, not floating-point
+        << OUT( 3.14'15'92     ) // double, single quotes ignored (C++14)
+        << OUT( 1.18e-4932l    ) // long double
+        << std::setprecision(39)
+        << OUT( 3.4028234e38f  ) // float
+        << OUT( 3.4028234e38   ) // double
+        << OUT( 3.4028234e38l  ) // long double
+        << '\n';
+
+    static_assert(3.4028234e38f == std::numeric_limits<float>::max());
+
+    static_assert(3.4028234e38f ==  // ends with 4
+                  3.4028235e38f);   // ends with 5
+
+    static_assert(3.4028234e38 !=   // ends with 4
+                  3.4028235e38);    // ends with 5
+
+    // Both floating-point constants below are 3.4028234e38
+    static_assert(3.4028234e38f !=  // a float (then promoted to double)
+                  3.4028234e38);    // a double
+}