[Docs] Add Doxygen docs generation to the make system

Makefile.am

@@ -292,6 +292,21 @@ CLEANFILES = $(OSX_DMG) $(RAVEN_WIN_INSTALLER)
 
 DISTCHECK_CONFIGURE_FLAGS = --enable-man
 
-clean-local:
+doc/doxygen/.stamp: doc/Doxyfile FORCE
+	$(MKDIR_P) $(@D)
+	$(DOXYGEN) $^
+	$(AM_V_at) touch $@
+
+if HAVE_DOXYGEN
+docs: doc/doxygen/.stamp
+else
+docs:
+	@echo "error: doxygen not found"
+endif
+
+clean-docs:
+	rm -rf doc/doxygen
+
+clean-local: clean-docs
 	rm -rf coverage_percent.txt test_raven.coverage/ total.coverage/ test/tmp/ cache/ $(OSX_APP)
 	rm -rf test/functional/__pycache__

configure.ac

@@ -94,6 +94,12 @@ AC_PATH_TOOL(READELF, readelf)
 AC_PATH_TOOL(CPPFILT, c++filt)
 AC_PATH_TOOL(OBJCOPY, objcopy)
 
+AC_PATH_PROG(DOXYGEN, doxygen)
+if test -z "$DOXYGEN"; then
+   AC_MSG_WARN([Doxygen not found])
+fi
+AM_CONDITIONAL([HAVE_DOXYGEN], [test -n "$DOXYGEN"])
+
 AC_ARG_VAR(PYTHONPATH, Augments the default search path for python module files)
 
 # Enable wallet
@@ -1242,7 +1248,7 @@ AC_SUBST(PROTOBUF_LIBS)
 AC_SUBST(QR_LIBS)
 AC_CONFIG_FILES([Makefile src/Makefile doc/man/Makefile share/setup.nsi share/qt/Info.plist test/config.ini])
 AC_CONFIG_FILES([contrib/devtools/split-debug.sh],[chmod +x contrib/devtools/split-debug.sh])
-AC_CONFIG_FILES([doc/Doxyfile])
+AM_COND_IF([HAVE_DOXYGEN], [AC_CONFIG_FILES([doc/Doxyfile])])
 AC_CONFIG_LINKS([contrib/filter-lcov.py:contrib/filter-lcov.py])
 AC_CONFIG_LINKS([test/functional/test_runner.py:test/functional/test_runner.py])
 AC_CONFIG_LINKS([test/util/raven-util-test.py:test/util/raven-util-test.py])

doc/developer-notes.md

@@ -129,9 +129,21 @@ Not OK (used plenty in the current source, but not picked up):
 //
 ```
 
-A full list of comment syntaxes picked up by doxygen can be found at http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html,
+A full list of comment syntaxes picked up by doxygen can be found at
+http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html,
 but if possible use one of the above styles.
 
+The Ravencoin Doxygen documentation can be generated by running `make docs` from the top-level 
+directory of the repository.
+That creates the documentation in the directory "doc/doxygen" and the it can be accessed by a browser at:
+    doc/doxygen/html/index.html    
+The documentation can by deleted by running `make clean-docs`.
+
+Before running `make docs`, you will need to install dependencies `doxygen` and `dot` (a component 
+of `graphviz`). For example, 
+    on MacOS via Homebrew: `brew install doxygen --with-graphviz`
+    on Debian/Ubuntu: `sudo install doxygen graphviz`
+
 Development tips and tricks
 ---------------------------
 

src/net_processing.h

@@ -67,7 +67,7 @@ class PeerLogicValidation final: public CValidationInterface, public NetEventsIn
     void EvictExtraOutboundPeers(int64_t time_in_seconds);
 
 private:
-    int64_t m_stale_tip_check_time; //! Next time to check for stale tip
+    int64_t m_stale_tip_check_time; //!< Next time to check for stale tip
 };
 
 struct CNodeStateStats {

src/netbase.cpp

@@ -193,10 +193,10 @@ enum SOCKSVersion: uint8_t {
 
 /** Values defined for METHOD in RFC1928 */
 enum SOCKS5Method: uint8_t {
-    NOAUTH = 0x00,        //! No authentication required
-    GSSAPI = 0x01,        //! GSSAPI
-    USER_PASS = 0x02,     //! Username/password
-    NO_ACCEPTABLE = 0xff, //! No acceptable methods
+    NOAUTH = 0x00,        //!< No authentication required
+    GSSAPI = 0x01,        //!< GSSAPI
+    USER_PASS = 0x02,     //!< Username/password
+    NO_ACCEPTABLE = 0xff, //!< No acceptable methods
 };
 
 /** Values defined for CMD in RFC1928 */
@@ -208,15 +208,15 @@ enum SOCKS5Command: uint8_t {
 
 /** Values defined for REP in RFC1928 */
 enum SOCKS5Reply: uint8_t {
-    SUCCEEDED = 0x00,        //! Succeeded
-    GENFAILURE = 0x01,       //! General failure
-    NOTALLOWED = 0x02,       //! Connection not allowed by ruleset
-    NETUNREACHABLE = 0x03,   //! Network unreachable
-    HOSTUNREACHABLE = 0x04,  //! Network unreachable
-    CONNREFUSED = 0x05,      //! Connection refused
-    TTLEXPIRED = 0x06,       //! TTL expired
-    CMDUNSUPPORTED = 0x07,   //! Command not supported
-    ATYPEUNSUPPORTED = 0x08, //! Address type not supported
+    SUCCEEDED = 0x00,        //!< Succeeded
+    GENFAILURE = 0x01,       //!< General failure
+    NOTALLOWED = 0x02,       //!< Connection not allowed by ruleset
+    NETUNREACHABLE = 0x03,   //!< Network unreachable
+    HOSTUNREACHABLE = 0x04,  //!< Network unreachable
+    CONNREFUSED = 0x05,      //!< Connection refused
+    TTLEXPIRED = 0x06,       //!< TTL expired
+    CMDUNSUPPORTED = 0x07,   //!< Command not supported
+    ATYPEUNSUPPORTED = 0x08, //!< Address type not supported
 };
 
 /** Values defined for ATYPE in RFC1928 */

src/policy/fees.h

@@ -96,9 +96,9 @@ std::string StringForFeeReason(FeeReason reason);
 
 /* Used to determine type of fee estimation requested */
 enum class FeeEstimateMode {
-    UNSET,        //! Use default settings based on other criteria
-    ECONOMICAL,   //! Force estimateSmartFee to use non-conservative estimates
-    CONSERVATIVE, //! Force estimateSmartFee to use conservative estimates
+    UNSET,        //!< Use default settings based on other criteria
+    ECONOMICAL,   //!< Force estimateSmartFee to use non-conservative estimates
+    CONSERVATIVE, //!< Force estimateSmartFee to use conservative estimates
 };
 
 bool FeeModeFromString(const std::string& mode_string, FeeEstimateMode& fee_estimate_mode);

src/primitives/transaction.h

@@ -70,7 +70,7 @@ class CTxIn
     COutPoint prevout;
     CScript scriptSig;
     uint32_t nSequence;
-    CScriptWitness scriptWitness; //! Only serialized through CTransaction
+    CScriptWitness scriptWitness; //!< Only serialized through CTransaction
 
     /* Setting nSequence to this value for every input in a transaction
      * disables nLockTime. */

src/txmempool.h

@@ -318,13 +318,13 @@ struct TxMempoolInfo
  * this is passed to the notification signal.
  */
 enum class MemPoolRemovalReason {
-    UNKNOWN = 0, //! Manually removed or unknown reason
-    EXPIRY,      //! Expired from mempool
-    SIZELIMIT,   //! Removed in size limiting
-    REORG,       //! Removed for reorganization
-    BLOCK,       //! Removed for block
-    CONFLICT,    //! Removed for conflict with in-block transaction
-    REPLACED     //! Removed for replacement
+    UNKNOWN = 0, //!< Manually removed or unknown reason
+    EXPIRY,      //!< Expired from mempool
+    SIZELIMIT,   //!< Removed in size limiting
+    REORG,       //!< Removed for reorganization
+    BLOCK,       //!< Removed for block
+    CONFLICT,    //!< Removed for conflict with in-block transaction
+    REPLACED,    //!< Removed for replacement
 };
 
 class SaltedTxidHasher