logging: add LogError, LogWarning, LogInfo, LogDebug, LogTrace

These provide simple and clear ways to write the most common logging
operations:

    LogInfo("msg");
    LogDebug(BCLog::LogFlags::NET, "msg");

    LogError("msg");
    LogWarning("msg");
    LogTrace(BCLog::LogFlags::NET, "msg");

For cases where the level cannot be hardcoded, LogPrintLevel(category,
level, ...) remains available.

doc/developer-notes.md

@@ -723,6 +723,44 @@ General Bitcoin Core
   - *Explanation*: If the test suite is to be updated for a change, this has to
     be done first.
 
+Logging
+-------
+
+The macros `LogInfo`, `LogDebug`, `LogTrace`, `LogWarning` and `LogError` are available for
+logging messages. They should be used as follows:
+
+- `LogDebug(BCLog::CATEGORY, fmt, params...)` is what you want
+  most of the time, and it should be used for log messages that are
+  useful for debugging and can reasonably be enabled on a production
+  system (that has sufficient free storage space). They will be logged
+  if bitcoind is started with `-debug=category` or `-debug=1`.
+
+- `LogInfo(fmt, params...)` should only be used rarely, eg for startup
+  messages or for infrequent and important events such as a new block
+  tip being found or a new outbound connection being made. These log
+  messages are unconditional so care must be taken that they can't be
+  used by an attacker to fill up storage.
+
+- `LogError(fmt, params...)` should be used in place of `LogInfo` for
+  severe problems that require the node (or a subsystem) to shut down
+  entirely (eg, insufficient storage space).
+
+- `LogWarning(fmt, params...)` should be used in place of `LogInfo` for
+  severe problems that the node admin should address, but are not
+  severe enough to warrant shutting down the node (eg, system time
+  appears to be wrong, unknown soft fork appears to have activated).
+
+- `LogTrace(BCLog::CATEGORY, fmt, params...) should be used in place of
+  `LogDebug` for log messages that would be unusable on a production
+  system, eg due to being too noisy in normal use, or too resource
+  intensive to process. These will be logged if the startup
+  options `-debug=category -loglevel=category:trace` or `-debug=1
+  -loglevel=trace` are selected.
+
+Note that the format strings and parameters of `LogDebug` and `LogTrace`
+are only evaluated if the logging category is enabled, so you must be
+careful to avoid side-effects in those expressions.
+
 Wallet
 -------
 
@@ -891,7 +929,7 @@ Strings and formatting
     `wcstoll`, `wcstombs`, `wcstoul`, `wcstoull`, `wcstoumax`, `wcswidth`,
     `wcsxfrm`, `wctob`, `wctomb`, `wctrans`, `wctype`, `wcwidth`, `wprintf`
 
-- For `strprintf`, `LogPrint`, `LogPrintf` formatting characters don't need size specifiers.
+- For `strprintf`, `LogInfo`, `LogDebug`, etc formatting characters don't need size specifiers.
 
   - *Rationale*: Bitcoin Core uses tinyformat, which is type safe. Leave them out to avoid confusion.
 
@@ -903,7 +941,7 @@ Strings and formatting
 
     - *Rationale*: Although this is guaranteed to be safe starting with C++11, `.data()` communicates the intent better.
 
-  - Do not use it when passing strings to `tfm::format`, `strprintf`, `LogPrint[f]`.
+  - Do not use it when passing strings to `tfm::format`, `strprintf`, `LogInfo`, `LogDebug`, etc.
 
     - *Rationale*: This is redundant. Tinyformat handles strings.
 

src/logging.h

@@ -237,9 +237,12 @@ static inline void LogPrintf_(const std::string& logging_function, const std::st
 #define LogPrintLevel_(category, level, ...) LogPrintf_(__func__, __FILE__, __LINE__, category, level, __VA_ARGS__)
 
 // Log unconditionally.
-#define LogPrintf(...) LogPrintLevel_(BCLog::LogFlags::NONE, BCLog::Level::Info, __VA_ARGS__)
+#define LogInfo(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Info, __VA_ARGS__)
+#define LogWarning(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Warning, __VA_ARGS__)
+#define LogError(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Error, __VA_ARGS__)
 
-// Log unconditionally, prefixing the output with the passed category name.
+// Deprecated unconditional logging.
+#define LogPrintf(...) LogInfo(__VA_ARGS__)
 #define LogPrintfCategory(category, ...) LogPrintLevel_(category, BCLog::Level::Info, __VA_ARGS__)
 
 // Use a macro instead of a function for conditional logging to prevent
@@ -254,7 +257,11 @@ static inline void LogPrintf_(const std::string& logging_function, const std::st
     } while (0)
 
 // Log conditionally, prefixing the output with the passed category name.
-#define LogPrint(category, ...)  LogPrintLevel(category, BCLog::Level::Debug, __VA_ARGS__)
+#define LogDebug(category, ...) LogPrintLevel(category, BCLog::Level::Debug, __VA_ARGS__)
+#define LogTrace(category, ...) LogPrintLevel(category, BCLog::Level::Trace, __VA_ARGS__)
+
+// Deprecated conditional logging
+#define LogPrint(category, ...)  LogDebug(category, __VA_ARGS__)
 
 template <typename... Args>
 bool error(const char* fmt, const Args&... args)

src/test/logging_tests.cpp

@@ -105,10 +105,11 @@ BOOST_FIXTURE_TEST_CASE(logging_LogPrintf_, LogSetup)
     BOOST_CHECK_EQUAL_COLLECTIONS(log_lines.begin(), log_lines.end(), expected.begin(), expected.end());
 }
 
-BOOST_FIXTURE_TEST_CASE(logging_LogPrintMacros, LogSetup)
+BOOST_FIXTURE_TEST_CASE(logging_LogPrintMacrosDeprecated, LogSetup)
 {
     LogPrintf("foo5: %s\n", "bar5");
     LogPrint(BCLog::NET, "foo6: %s\n", "bar6");
+    LogPrintLevel(BCLog::NET, BCLog::Level::Trace, "foo4: %s\n", "bar4"); // not logged
     LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "foo7: %s\n", "bar7");
     LogPrintLevel(BCLog::NET, BCLog::Level::Info, "foo8: %s\n", "bar8");
     LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "foo9: %s\n", "bar9");
@@ -131,6 +132,27 @@ BOOST_FIXTURE_TEST_CASE(logging_LogPrintMacros, LogSetup)
     BOOST_CHECK_EQUAL_COLLECTIONS(log_lines.begin(), log_lines.end(), expected.begin(), expected.end());
 }
 
+BOOST_FIXTURE_TEST_CASE(logging_LogPrintMacros, LogSetup)
+{
+    LogTrace(BCLog::NET, "foo6: %s\n", "bar6"); // not logged
+    LogDebug(BCLog::NET, "foo7: %s\n", "bar7");
+    LogInfo("foo8: %s\n", "bar8");
+    LogWarning("foo9: %s\n", "bar9");
+    LogError("foo10: %s\n", "bar10");
+    std::ifstream file{tmp_log_path};
+    std::vector<std::string> log_lines;
+    for (std::string log; std::getline(file, log);) {
+        log_lines.push_back(log);
+    }
+    std::vector<std::string> expected = {
+        "[net] foo7: bar7",
+        "foo8: bar8",
+        "[warning] foo9: bar9",
+        "[error] foo10: bar10",
+    };
+    BOOST_CHECK_EQUAL_COLLECTIONS(log_lines.begin(), log_lines.end(), expected.begin(), expected.end());
+}
+
 BOOST_FIXTURE_TEST_CASE(logging_LogPrintMacros_CategoryName, LogSetup)
 {
     LogInstance().EnableCategory(BCLog::LogFlags::ALL);

test/lint/lint-format-strings.py

@@ -20,6 +20,11 @@
     'fprintf,1',
     'tfm::format,1',  # Assuming tfm::::format(std::ostream&, ...
     'LogConnectFailure,1',
+    'LogError,0',
+    'LogWarning,0',
+    'LogInfo,0',
+    'LogDebug,1',
+    'LogTrace,1',
     'LogPrint,1',
     'LogPrintf,0',
     'LogPrintfCategory,1',