Add stringification support to std::exception and deriving classes

This support is based on overriden `std::exception::what` method, so
if an exception does not do so meaningfully, the message is still
pointless.

This is only used as a fallback, both `StringMaker` specialization and
`operator<<` overload have priority..

include/internal/catch_tostring.h

@@ -62,7 +62,9 @@ namespace Catch {
         std::string convertUnknownEnumToString( E e );
 
         template<typename T>
-        typename std::enable_if<!std::is_enum<T>::value, std::string>::type convertUnstreamable( T const& value ) {
+        typename std::enable_if<
+            !std::is_enum<T>::value && !std::is_base_of<std::exception, T>::value,
+        std::string>::type convertUnstreamable( T const& value ) {
 #if !defined(CATCH_CONFIG_FALLBACK_STRINGIFIER)
             (void)value;
             return Detail::unprintableString;
@@ -71,11 +73,20 @@ namespace Catch {
 #endif
         }
         template<typename T>
-        typename std::enable_if<std::is_enum<T>::value, std::string>::type convertUnstreamable( T const& value ) {
+        typename std::enable_if<
-            return convertUnknownEnumToString( value );
+            !std::is_enum<T>::value && std::is_base_of<std::exception, T>::value,
+         std::string>::type convertUnstreamable(T const& ex) {
+            return ex.what();
         }
 
 
+        template<typename T>
+        typename std::enable_if<
+            std::is_enum<T>::value
+        , std::string>::type convertUnstreamable( T const& value ) {
+            return convertUnknownEnumToString( value );
+        }
+
 #if defined(_MANAGED)
         //! Convert a CLR string to a utf8 std::string
         template<typename T>

projects/SelfTest/Baselines/compact.sw.approved.txt

@@ -211,14 +211,21 @@ Matchers.tests.cpp:<line number>: passed: testStringForMatching(), Equals("this
 Matchers.tests.cpp:<line number>: passed: testStringForMatching(), Equals("this string contains 'ABC' as a substring", Catch::CaseSensitive::No) for: "this string contains 'abc' as a substring" equals: "this string contains 'abc' as a substring" (case insensitive)
 Matchers.tests.cpp:<line number>: failed: testStringForMatching(), Equals("this string contains 'ABC' as a substring") for: "this string contains 'abc' as a substring" equals: "this string contains 'ABC' as a substring"
 Matchers.tests.cpp:<line number>: failed: testStringForMatching(), Equals("something else", Catch::CaseSensitive::No) for: "this string contains 'abc' as a substring" equals: "something else" (case insensitive)
+ToStringGeneral.tests.cpp:<line number>: passed: ::Catch::Detail::stringify(WhatException{}) == "This exception has overriden what() method" for: "This exception has overriden what() method"
+==
+"This exception has overriden what() method"
+ToStringGeneral.tests.cpp:<line number>: passed: ::Catch::Detail::stringify(OperatorException{}) == "OperatorException" for: "OperatorException" == "OperatorException"
+ToStringGeneral.tests.cpp:<line number>: passed: ::Catch::Detail::stringify(StringMakerException{}) == "StringMakerException" for: "StringMakerException"
+==
+"StringMakerException"
 Matchers.tests.cpp:<line number>: failed: expected exception, got none; expression was: doesNotThrow(), SpecialException, ExceptionMatcher{1}
 Matchers.tests.cpp:<line number>: failed: expected exception, got none; expression was: doesNotThrow(), SpecialException, ExceptionMatcher{1}
 Matchers.tests.cpp:<line number>: failed: unexpected exception with message: 'Unknown exception'; expression was: throwsAsInt(1), SpecialException, ExceptionMatcher{1}
 Matchers.tests.cpp:<line number>: failed: unexpected exception with message: 'Unknown exception'; expression was: throwsAsInt(1), SpecialException, ExceptionMatcher{1}
-Matchers.tests.cpp:<line number>: failed: throws(3), SpecialException, ExceptionMatcher{1} for: {?} special exception has value of 1
+Matchers.tests.cpp:<line number>: failed: throws(3), SpecialException, ExceptionMatcher{1} for: std::exception special exception has value of 1
-Matchers.tests.cpp:<line number>: failed: throws(4), SpecialException, ExceptionMatcher{1} for: {?} special exception has value of 1
+Matchers.tests.cpp:<line number>: failed: throws(4), SpecialException, ExceptionMatcher{1} for: std::exception special exception has value of 1
-Matchers.tests.cpp:<line number>: passed: throws(1), SpecialException, ExceptionMatcher{1} for: {?} special exception has value of 1
+Matchers.tests.cpp:<line number>: passed: throws(1), SpecialException, ExceptionMatcher{1} for: std::exception special exception has value of 1
-Matchers.tests.cpp:<line number>: passed: throws(2), SpecialException, ExceptionMatcher{2} for: {?} special exception has value of 2
+Matchers.tests.cpp:<line number>: passed: throws(2), SpecialException, ExceptionMatcher{2} for: std::exception special exception has value of 2
 Exception.tests.cpp:<line number>: passed: thisThrows(), "expected exception" for: "expected exception" equals: "expected exception"
 Exception.tests.cpp:<line number>: passed: thisThrows(), Equals( "expecteD Exception", Catch::CaseSensitive::No ) for: "expected exception" equals: "expected exception" (case insensitive)
 Exception.tests.cpp:<line number>: passed: thisThrows(), StartsWith( "expected" ) for: "expected exception" starts with: "expected"

projects/SelfTest/Baselines/console.std.approved.txt

@@ -335,12 +335,12 @@ Matchers.tests.cpp:<line number>
 Matchers.tests.cpp:<line number>: FAILED:
   CHECK_THROWS_MATCHES( throws(3), SpecialException, ExceptionMatcher{1} )
 with expansion:
-  {?} special exception has value of 1
+  std::exception special exception has value of 1
 
 Matchers.tests.cpp:<line number>: FAILED:
   REQUIRE_THROWS_MATCHES( throws(4), SpecialException, ExceptionMatcher{1} )
 with expansion:
-  {?} special exception has value of 1
+  std::exception special exception has value of 1
 
 -------------------------------------------------------------------------------
 Expected exceptions that don't throw or unexpected exceptions fail the test
@@ -1084,6 +1084,6 @@ due to unexpected exception with message:
   Why would you throw a std::string?
 
 ===============================================================================
-test cases:  206 | 153 passed |  49 failed |  4 failed as expected
+test cases:  207 | 154 passed |  49 failed |  4 failed as expected
-assertions: 1061 | 933 passed | 107 failed | 21 failed as expected
+assertions: 1064 | 936 passed | 107 failed | 21 failed as expected
 

projects/SelfTest/Baselines/console.sw.approved.txt

@@ -1680,6 +1680,34 @@ with expansion:
   "this string contains 'abc' as a substring" equals: "something else" (case
   insensitive)
 
+-------------------------------------------------------------------------------
+Exception as a value (e.g. in REQUIRE_THROWS_MATCHES) can be stringified
+-------------------------------------------------------------------------------
+ToStringGeneral.tests.cpp:<line number>
+...............................................................................
+
+ToStringGeneral.tests.cpp:<line number>:
+PASSED:
+  REQUIRE( ::Catch::Detail::stringify(WhatException{}) == "This exception has overriden what() method" )
+with expansion:
+  "This exception has overriden what() method"
+  ==
+  "This exception has overriden what() method"
+
+ToStringGeneral.tests.cpp:<line number>:
+PASSED:
+  REQUIRE( ::Catch::Detail::stringify(OperatorException{}) == "OperatorException" )
+with expansion:
+  "OperatorException" == "OperatorException"
+
+ToStringGeneral.tests.cpp:<line number>:
+PASSED:
+  REQUIRE( ::Catch::Detail::stringify(StringMakerException{}) == "StringMakerException" )
+with expansion:
+  "StringMakerException"
+  ==
+  "StringMakerException"
+
 -------------------------------------------------------------------------------
 Exception matchers that fail
   No exception
@@ -1722,12 +1750,12 @@ Matchers.tests.cpp:<line number>
 Matchers.tests.cpp:<line number>: FAILED:
   CHECK_THROWS_MATCHES( throws(3), SpecialException, ExceptionMatcher{1} )
 with expansion:
-  {?} special exception has value of 1
+  std::exception special exception has value of 1
 
 Matchers.tests.cpp:<line number>: FAILED:
   REQUIRE_THROWS_MATCHES( throws(4), SpecialException, ExceptionMatcher{1} )
 with expansion:
-  {?} special exception has value of 1
+  std::exception special exception has value of 1
 
 -------------------------------------------------------------------------------
 Exception matchers that succeed
@@ -1739,13 +1767,13 @@ Matchers.tests.cpp:<line number>:
 PASSED:
   CHECK_THROWS_MATCHES( throws(1), SpecialException, ExceptionMatcher{1} )
 with expansion:
-  {?} special exception has value of 1
+  std::exception special exception has value of 1
 
 Matchers.tests.cpp:<line number>:
 PASSED:
   REQUIRE_THROWS_MATCHES( throws(2), SpecialException, ExceptionMatcher{2} )
 with expansion:
-  {?} special exception has value of 2
+  std::exception special exception has value of 2
 
 -------------------------------------------------------------------------------
 Exception messages can be tested for
@@ -8950,6 +8978,6 @@ Misc.tests.cpp:<line number>:
 PASSED:
 
 ===============================================================================
-test cases:  206 | 140 passed |  62 failed |  4 failed as expected
+test cases:  207 | 141 passed |  62 failed |  4 failed as expected
-assertions: 1075 | 933 passed | 121 failed | 21 failed as expected
+assertions: 1078 | 936 passed | 121 failed | 21 failed as expected
 

projects/SelfTest/Baselines/junit.sw.approved.txt

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuitesloose text artifact
 >
-  <testsuite name="<exe-name>" errors="17" failures="105" tests="1076" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="105" tests="1079" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <testcase classname="<exe-name>.global" name="# A test name that starts with a #" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="#1005: Comparing pointer to int and long (NULL can be either on various systems)" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="#1027" time="{duration}"/>
@@ -218,6 +218,7 @@ Matchers.tests.cpp:<line number>
 Matchers.tests.cpp:<line number>
       </failure>
     </testcase>
+    <testcase classname="<exe-name>.global" name="Exception as a value (e.g. in REQUIRE_THROWS_MATCHES) can be stringified" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Exception matchers that fail/No exception" time="{duration}">
       <failure message="doesNotThrow(), SpecialException, ExceptionMatcher{1}" type="CHECK_THROWS_MATCHES">
 Matchers.tests.cpp:<line number>
@@ -237,10 +238,10 @@ Matchers.tests.cpp:<line number>
       </error>
     </testcase>
     <testcase classname="<exe-name>.global" name="Exception matchers that fail/Contents are wrong" time="{duration}">
-      <failure message="{?} special exception has value of 1" type="CHECK_THROWS_MATCHES">
+      <failure message="std::exception special exception has value of 1" type="CHECK_THROWS_MATCHES">
 Matchers.tests.cpp:<line number>
       </failure>
-      <failure message="{?} special exception has value of 1" type="REQUIRE_THROWS_MATCHES">
+      <failure message="std::exception special exception has value of 1" type="REQUIRE_THROWS_MATCHES">
 Matchers.tests.cpp:<line number>
       </failure>
     </testcase>

projects/SelfTest/Baselines/xml.sw.approved.txt

@@ -1901,6 +1901,37 @@
       </Expression>
       <OverallResult success="false"/>
     </TestCase>
+    <TestCase name="Exception as a value (e.g. in REQUIRE_THROWS_MATCHES) can be stringified" tags="[exception][toString]" filename="projects/<exe-name>/UsageTests/ToStringGeneral.tests.cpp" >
+      <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/UsageTests/ToStringGeneral.tests.cpp" >
+        <Original>
+          ::Catch::Detail::stringify(WhatException{}) == "This exception has overriden what() method"
+        </Original>
+        <Expanded>
+          "This exception has overriden what() method"
+==
+"This exception has overriden what() method"
+        </Expanded>
+      </Expression>
+      <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/UsageTests/ToStringGeneral.tests.cpp" >
+        <Original>
+          ::Catch::Detail::stringify(OperatorException{}) == "OperatorException"
+        </Original>
+        <Expanded>
+          "OperatorException" == "OperatorException"
+        </Expanded>
+      </Expression>
+      <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/UsageTests/ToStringGeneral.tests.cpp" >
+        <Original>
+          ::Catch::Detail::stringify(StringMakerException{}) == "StringMakerException"
+        </Original>
+        <Expanded>
+          "StringMakerException"
+==
+"StringMakerException"
+        </Expanded>
+      </Expression>
+      <OverallResult success="true"/>
+    </TestCase>
     <TestCase name="Exception matchers that fail" tags="[!throws][.][.failing][exceptions][matchers]" filename="projects/<exe-name>/UsageTests/Matchers.tests.cpp" >
       <Section name="No exception" filename="projects/<exe-name>/UsageTests/Matchers.tests.cpp" >
         <Expression success="false" type="CHECK_THROWS_MATCHES" filename="projects/<exe-name>/UsageTests/Matchers.tests.cpp" >
@@ -1952,7 +1983,7 @@
             throws(3), SpecialException, ExceptionMatcher{1}
           </Original>
           <Expanded>
-            {?} special exception has value of 1
+            std::exception special exception has value of 1
           </Expanded>
         </Expression>
         <Expression success="false" type="REQUIRE_THROWS_MATCHES" filename="projects/<exe-name>/UsageTests/Matchers.tests.cpp" >
@@ -1960,7 +1991,7 @@
             throws(4), SpecialException, ExceptionMatcher{1}
           </Original>
           <Expanded>
-            {?} special exception has value of 1
+            std::exception special exception has value of 1
           </Expanded>
         </Expression>
         <OverallResults successes="0" failures="2" expectedFailures="0"/>
@@ -1973,7 +2004,7 @@
           throws(1), SpecialException, ExceptionMatcher{1}
         </Original>
         <Expanded>
-          {?} special exception has value of 1
+          std::exception special exception has value of 1
         </Expanded>
       </Expression>
       <Expression success="true" type="REQUIRE_THROWS_MATCHES" filename="projects/<exe-name>/UsageTests/Matchers.tests.cpp" >
@@ -1981,7 +2012,7 @@
           throws(2), SpecialException, ExceptionMatcher{2}
         </Original>
         <Expanded>
-          {?} special exception has value of 2
+          std::exception special exception has value of 2
         </Expanded>
       </Expression>
       <OverallResult success="true"/>
@@ -9892,7 +9923,7 @@ loose text artifact
       </Section>
       <OverallResult success="true"/>
     </TestCase>
-    <OverallResults successes="933" failures="122" expectedFailures="21"/>
+    <OverallResults successes="936" failures="122" expectedFailures="21"/>
   </Group>
-  <OverallResults successes="933" failures="121" expectedFailures="21"/>
+  <OverallResults successes="936" failures="121" expectedFailures="21"/>
 </Catch>

projects/SelfTest/UsageTests/ToStringGeneral.tests.cpp

@@ -115,3 +115,46 @@ TEST_CASE("Static arrays are convertible to string", "[toString]") {
         REQUIRE(Catch::Detail::stringify(arr) == R"({ { "1:1", "1:2", "1:3" }, { "2:1", "2:2" } })");
     }
 }
+
+struct WhatException : std::exception {
+    char const* what() const noexcept override {
+        return "This exception has overriden what() method";
+    }
+    ~WhatException() override;
+};
+
+struct OperatorException : std::exception {
+    ~OperatorException() override;
+};
+
+std::ostream& operator<<(std::ostream& out, OperatorException const&) {
+    out << "OperatorException";
+    return out;
+}
+
+struct StringMakerException : std::exception {
+    ~StringMakerException() override;
+};
+
+namespace Catch {
+template <>
+struct StringMaker<StringMakerException> {
+    static std::string convert(StringMakerException const&) {
+        return "StringMakerException";
+    }
+};
+}
+
+// Avoid -Wweak-tables
+WhatException::~WhatException() = default;
+OperatorException::~OperatorException() = default;
+StringMakerException::~StringMakerException() = default;
+
+
+
+
+TEST_CASE("Exception as a value (e.g. in REQUIRE_THROWS_MATCHES) can be stringified", "[toString][exception]") {
+    REQUIRE(::Catch::Detail::stringify(WhatException{}) == "This exception has overriden what() method");
+    REQUIRE(::Catch::Detail::stringify(OperatorException{}) == "OperatorException");
+    REQUIRE(::Catch::Detail::stringify(StringMakerException{}) == "StringMakerException");
+}