Improve error classes

 - Make 'msg' an attribute on our common error hierarchies
 - Report the error summary in the CLI even in non-verbose mode.

pyhanko/cli.py

@@ -101,20 +101,21 @@ def pyhanko_exception_manager():
         exception = e
         msg = (
             "Failed to read PDF file in strict mode; rerun with "
-            "--no-strict-syntax to try again"
+            "--no-strict-syntax to try again.\n"
+            f"Error message: {e.msg}"
         )
     except misc.PdfReadError as e:
         exception = e
-        msg = "Failed to read PDF file."
+        msg = f"Failed to read PDF file: {e.msg}"
     except misc.PdfWriteError as e:
         exception = e
-        msg = "Failed to write PDF file."
+        msg = f"Failed to write PDF file: {e.msg}"
     except SigningError as e:
         exception = e
-        msg = "Error raised while producing signed file."
+        msg = f"Error raised while producing signed file: {e.msg}"
     except LayoutError as e:
         exception = e
-        msg = "Error raised while producing signature layout."
+        msg = f"Error raised while producing signature layout: {e.msg}"
     except Exception as e:
         exception = e
         msg = "Generic processing error."

pyhanko/pdf_utils/layout.py

@@ -19,12 +19,16 @@
 
 class LayoutError(ValueError):
     """Indicates an error in a layout computation."""
-    pass
+
+    def __init__(self, msg: str, *args):
+        self.msg = msg
+        super().__init__(msg, *args)
 
 
 class BoxSpecificationError(LayoutError):
     """Raised when a box constraint is over/underspecified."""
-    pass
+    def __init__(self, msg: Optional[str] = None):
+        super().__init__(msg=msg or "box constraint is over/underspecified")
 
 
 class BoxConstraints:

pyhanko/pdf_utils/misc.py

@@ -187,7 +187,10 @@ def __str__(self):
 
 
 class PdfError(Exception):
-    pass
+
+    def __init__(self, msg: str, *args):
+        self.msg = msg
+        super().__init__(msg, *args)
 
 
 class PdfReadError(PdfError):
@@ -199,7 +202,8 @@ class PdfStrictReadError(PdfReadError):
 
 
 class IndirectObjectExpected(PdfReadError):
-    pass
+    def __init__(self, msg: Optional[str] = None):
+        super().__init__(msg=msg or "indirect object expected")
 
 
 class PdfWriteError(PdfError):

pyhanko/sign/general.py

@@ -297,7 +297,9 @@ class SigningError(ValueError):
     """
     Error encountered while signing a file.
     """
-    pass
+    def __init__(self, msg: str, *args):
+        self.msg = msg
+        super().__init__(msg, *args)
 
 
 class UnacceptableSignerError(SigningError):