Cpp codegen: handling of imported exceptions. Fixes #3571 (#7360)

tests/exception/tcpp_imported_exc.nim

@@ -0,0 +1,134 @@
+discard """
+targets: "cpp"
+output: '''caught as std::exception
+expected
+finally1
+finally2
+finally2
+2
+expected
+finally 1
+finally 2
+expected
+cpp exception caught
+'''
+"""
+
+type 
+  std_exception* {.importcpp: "std::exception", header: "<exception>".} = object
+  std_runtime_error* {.importcpp: "std::runtime_error", header: "<stdexcept>".} = object
+  std_string* {.importcpp: "std::string", header: "<string>".} = object
+
+proc constructStdString(s: cstring): std_string {.importcpp: "std::string(@)", constructor, header: "<string>".}
+
+proc constructRuntimeError(s: stdstring): std_runtime_error {.importcpp: "std::runtime_error(@)", constructor.}
+
+proc what(ex: std_runtime_error): cstring {.importcpp: "((char *)#.what())".}
+
+proc myexception = 
+  raise constructRuntimeError(constructStdString("cpp_exception"))
+
+try:
+  myexception() # raise std::runtime_error
+except std_exception:
+  echo "caught as std::exception"
+  try:
+    raise constructStdString("x")
+  except std_exception:
+    echo "should not happen"
+  except:
+    echo "expected"
+
+doAssert(getCurrentException() == nil)
+
+proc earlyReturn = 
+  try:
+    try:
+        myexception()
+    finally:
+      echo "finally1"
+  except:
+    return
+  finally:
+    echo "finally2"
+  
+earlyReturn()
+doAssert(getCurrentException() == nil)
+
+
+try:
+  block blk1:
+    try:
+      raise newException(ValueError, "mmm")
+    except:
+      break blk1
+except:
+  echo "should not happen"
+finally:
+  echo "finally2"
+
+doAssert(getCurrentException() == nil)
+
+#--------------------------------------
+
+# raise by pointer and also generic type
+
+type
+  std_vector {.importcpp"std::vector", header"<vector>".} [T] = object
+
+proc newVector[T](len: int): ptr std_vector[T] {.importcpp: "new std::vector<'1>(@)".}
+proc deleteVector[T](v: ptr std_vector[T]) {.importcpp: "delete @; @ = NIM_NIL;".}
+proc len[T](v: std_vector[T]): uint {.importcpp: "size".}
+
+var v = newVector[int](2)
+try:
+  try:
+    try:
+      raise v
+    except ptr std_vector[int] as ex:
+      echo len(ex[])
+      raise newException(ValueError, "msg5")
+    except:
+      echo "should not happen"
+  finally:
+    deleteVector(v)
+except:
+  echo "expected"
+
+doAssert(v == nil)
+doAssert(getCurrentException() == nil)
+
+#--------------------------------------
+
+# mix of Nim and imported exceptions
+try:
+  try:
+    try:
+      raise newException(KeyError, "msg1")
+    except KeyError:
+      raise newException(ValueError, "msg2")
+    except:
+      echo "should not happen"
+    finally:
+      echo "finally 1"
+  except:
+    doAssert(getCurrentExceptionMsg() == "msg2")
+    raise constructStdString("std::string")
+  finally:
+    echo "finally 2"
+except:
+  echo "expected"
+  
+  
+doAssert(getCurrentException() == nil)
+
+try:
+    try:
+      myexception()
+    except std_runtime_error as ex:
+      echo "cpp exception caught"
+      raise newException(ValueError, "rewritten " & $ex.what())
+except:
+  doAssert(getCurrentExceptionMsg() == "rewritten cpp_exception")
+
+doAssert(getCurrentException() == nil)