Make logging more readable by removing noisy prefixes on filenames.

c++/src/kj/debug-test.c++

@@ -182,6 +182,8 @@ public:
 #endif
 
 std::string fileLine(std::string file, int line) {
+  file = trimSourceFilename(file.c_str()).cStr();
+
   file += ':';
   char buffer[32];
   sprintf(buffer, "%d", line);
@@ -266,7 +268,7 @@ TEST(Debug, Exception) {
   int line = __LINE__; Exception exception = KJ_EXCEPTION(DISCONNECTED, "foo", i);
 
   EXPECT_EQ(Exception::Type::DISCONNECTED, exception.getType());
-  EXPECT_STREQ(__FILE__, exception.getFile());
+  EXPECT_TRUE(kj::StringPtr(__FILE__).endsWith(exception.getFile()));
   EXPECT_EQ(line, exception.getLine());
   EXPECT_EQ("foo; i = 123", exception.getDescription());
 }

c++/src/kj/debug.c++

@@ -268,7 +268,7 @@ static String makeDescriptionImpl(DescriptionStyle style, const char* code, int
 
 void Debug::logInternal(const char* file, int line, LogSeverity severity, const char* macroArgs,
                         ArrayPtr<String> argValues) {
-  getExceptionCallback().logMessage(severity, file, line, 0,
+  getExceptionCallback().logMessage(severity, trimSourceFilename(file).cStr(), line, 0,
       makeDescriptionImpl(LOG, nullptr, 0, macroArgs, argValues));
 }
 

c++/src/kj/exception-test.c++

@@ -27,6 +27,10 @@ namespace kj {
 namespace _ {  // private
 namespace {
 
+TEST(Exception, TrimSourceFilename) {
+  EXPECT_EQ(trimSourceFilename(__FILE__), "kj/exception-test.c++");
+}
+
 TEST(Exception, RunCatchingExceptions) {
   bool recovered = false;
   Maybe<Exception> e = kj::runCatchingExceptions([&]() {

c++/src/kj/exception.c++

@@ -207,6 +207,28 @@ void printStackTraceOnCrash() {
 #endif
 }
 
+kj::StringPtr trimSourceFilename(kj::StringPtr filename) {
+  // Removes noisy prefixes from source code file name.
+
+  static constexpr const char* PREFIXES[] = {
+    "../",
+    "/ekam-provider/canonical/",
+    "/ekam-provider/c++header/",
+    "src/",
+    "tmp/"
+  };
+
+retry:
+  for (const char* prefix: PREFIXES) {
+    if (filename.startsWith(prefix)) {
+      filename = filename.slice(strlen(prefix));
+      goto retry;
+    }
+  }
+
+  return filename;
+}
+
 StringPtr KJ_STRINGIFY(Exception::Type type) {
   static const char* TYPE_STRINGS[] = {
     "failed",
@@ -253,12 +275,12 @@ String KJ_STRINGIFY(const Exception& e) {
 }
 
 Exception::Exception(Type type, const char* file, int line, String description) noexcept
-    : file(file), line(line), type(type), description(mv(description)) {
+    : file(trimSourceFilename(file).cStr()), line(line), type(type), description(mv(description)) {
   traceCount = kj::getStackTrace(trace).size();
 }
 
 Exception::Exception(Type type, String file, int line, String description) noexcept
-    : ownFile(kj::mv(file)), file(ownFile.cStr()), line(line), type(type),
+    : ownFile(kj::mv(file)), file(trimSourceFilename(ownFile).cStr()), line(line), type(type),
       description(mv(description)) {
   traceCount = kj::getStackTrace(trace).size();
 }

c++/src/kj/exception.h

@@ -307,6 +307,10 @@ void printStackTraceOnCrash();
 // a stack trace. You should call this as early as possible on program startup. Programs using
 // KJ_MAIN get this automatically.
 
+kj::StringPtr trimSourceFilename(kj::StringPtr filename);
+// Given a source code file name, trim off noisy prefixes like "src/" or
+// "/ekam-provider/canonical/".
+
 }  // namespace kj
 
 #endif  // KJ_EXCEPTION_H_