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issue COMPILER-DIAGNOSTICS, version 4
- To: firstname.lastname@example.org
- Subject: issue COMPILER-DIAGNOSTICS, version 4
- From: email@example.com (Sandra J Loosemore)
- Date: Tue, 1 Nov 88 10:21:08 MST
Here is a new version of the writeup on this issue which incorporates
suggestions from Pitman and Gray. I am not yet entirely happy with
section 2 of the proposal (see the discussion section) but I wanted to
get some feedback on the general direction this is going in, before
doing more work on it.
References: CLtL p. 438-439
Condition System, Revision #18
Category: CLARIFICATION, ENHANCEMENT
Edit History: V1, 15 Oct 1988, Sandra Loosemore
V2, 19 Oct 1988, Sandra Loosemore (minor fixes)
V3, 25 Oct 1988, Sandra Loosemore (input from Pitman & Gray)
V4, 01 Nov 1988, Sandra Loosemore (fix typos)
It is unclear whether various diagnostics issued by the compiler are
supposed to be true errors and warnings, or merely messages.
In some implementations, COMPILE-FILE handles even serious error
situations (such as syntax errors) by printing a message and then
trying to recover and continue compiling the rest of the file, rather
than by signalling an error. While this user interface style is just
as acceptable as invoking the debugger, it means that a normal return
from COMPILE-FILE does not necessarily imply that the file was
Many compilers issue warnings about programming style issues (such as
binding a variable that is never used but not declared IGNORE).
Sometimes these messages obscure warnings about more serious problems,
and there should be some way to differentiate between the two. For
example, it should be possible to suppress the style warnings.
Also, neither CLtL nor issue RETURN-VALUES-UNSPECIFIED states what the
return value from COMPILE-FILE should be.
(1) Clarify that COMPILE-FILE is allowed to print messages to
*STANDARD-OUTPUT* indicating the normal progress of the compilation.
(See issue COMPILER-VERBOSITY.)
(2) Clarify that both ERROR and WARNING conditions may be signalled within
COMPILE or COMPILE-FILE, including arbitrary errors which may occur
due to compile-time processing of (EVAL-WHEN (COMPILE) ...) forms or
Considering only those conditions signalled -by- the compiler (as
opposed to -within- the compiler),
(a) Conditions of type ERROR may be signalled by the compiler in
situations where the compilation cannot proceed without
(b) Conditions of type WARNING may be signalled by the compiler in
situations where the standard explicitly states that a warning must,
should, or may be signalled; and where the compiler can determine
that a situation that "is an error" would result at runtime.
violation of type declarations
SETQ'ing a constant defined with DEFCONSTANT
calls to built-in Lisp functions with wrong number of arguments
referencing a variable declared IGNORE
(c) All other diagnostics issued by the compiler should be conditions
of type NOTICE. In particular, this category includes all
diagnostics about matters of programming style. Although
conditions of type NOTICE -may- be signalled in these situations,
no implementation is -required- to do so. However, if an
implementation does choose to signal a condition, that condition
will be of type NOTICE.
redefinition of function with different argument list
unreferenced local variables not declared IGNORE
(3) Require COMPILE-FILE to establish an error handler. Add a :HANDLER
keyword argument to COMPILE-FILE, which is a user condition
handler function which is to be used during compilation. If the
user error handler is not supplied or declines to handle a condition,
then the compiler's error handler will be invoked. Require the
compiler's error handler to handle the ABORT restart by aborting
the smallest feasible part of the compilation.
(4) Specify that COMPILE-FILE returns three values. The first value is the
truename of the output file, or NIL if the file could not be created.
The second value is non-NIL if errors were signalled during compilation
(indicating that the output file is almost certainly unusable). The
third value is non-NIL if warnings were signalled during compilation
(indicating that the output file may or may not be usable).
(5) Clarify that COMPILE does not establish a condition handler. Instead,
it uses whatever condition handler has been established in the environment
from which it is called.
Point by point,
(1) This reflects current practice.
(2) Conditions such as syntax errors which are errors in the interpreter
remain errors in the compiler. The division of other conditions
into WARNINGs and NOTICEs allows potentially serious problems to be
distinguished from mere kibbitzing on the part of the compiler.
(3) It is reasonable for the default handling of compiler errors not to
cause the debugger to be invoked. However, any error handler
established by COMPILE-FILE would override handlers established by the
user in the surrounding environment.
Requiring the compiler's error handler to handle the ABORT restart
reflects what several implementations already do (although probably not
using this mechanism). The intent of the wording is to allow an
implementation to abort the entire file compilation if it is not
feasible to abort a smaller part.
(4) This allows users to determine whether or not COMPILE-FILE is able to
actually compile the file successfully. Returning several values is
is more useful than a single success/failure value because there are
several degrees of failure.
(5) This is to reflect the use of COMPILE-FILE as being more "batch"-oriented
and COMPILE as being more interactive. There is less motivation to have
COMPILE try to recover from errors without user interaction.
No implementation behaves exactly as specified in this proposal.
In VaxLisp, COMPILE-FILE handles most compile-time errors without
invoking the debugger. (It gives up on that top-level form and moves on
to the next one.) Instead of signalling errors or warnings, it simply
prints them out as messages.
In Lucid Common Lisp, COMPILE-FILE invokes the debugger when it encounters
serious problems. COMPILE-FILE returns the pathname for the output file.
Symbolics Genera usually tries to keep compiling when it encounters errors;
so does Symbolics Cloe.
On the TI Explorer, the compiler tries to catch most errors and turn
them into warnings (except for errors on opening a file), but the user
can change special variable COMPILER:WARN-ON-ERRORS to NIL if he wants
to enter the debugger on an error signalled during reading, macro
expansion, or compile-time evaluation. The true name of the output
file is returned as the first value. A second value indicates whether
any errors or warnings were reported.
Cost to implementors:
The cost to implementors is not trivial but not particularly high. This
proposal tries to allow implementations considerable freedom in what
kinds of conditions the compiler must detect and how they are handled,
while still allowing users some reasonably portable ways to deal with
Cost to users:
This is a compatible extension. This proposal may cause users to see
some small differences in the user interface to the compiler, but
implementations already vary quite widely in their approaches. Some
users will probably have to make some minor changes to their code.
Users are given a way to detect and handle compilation errors, which
would simplify the implementation of portable code-maintenance
utilities. The behavior of the compiler in error situations is made
more uniform across implementations.
The issue of normal progress messages from the compiler is discussed
in more detail in a separate issue, COMPILER-VERBOSITY.
Pitman says that he would like to require COMPILE-FILE's error handler
never to invoke the debugger. I have left that out of this proposal
because it seems like an unnecessary restriction; if users want to ensure
that kind of behavior it is possible to do so by supplying a user error
handler. (Of course, the converse is also true.)
Sections 2b and 2c need more work. In CLtL, everything has been lumped
together as warnings, but there seems to be general agreement that
some things (like complaints about unused variables) should really be
notices instead. Basically we need to go through and find every place
where CLtL says that the compiler might issue a warning and decide what
category it belongs in, and list it here.
This proposal, as it stands, doesn't propose to add any new conditions
specific to the compiler. We might consider introducing a
COMPILER-CONDITION that can be used in mixins with the other condition
types, so that error handlers can distinguish between errors signalled
by the compiler itself and errors signalled during macroexpansion or
Gray would like to exclude errors resulting from failure to open the
input and output files from the compiler's error handling. The
proposal should probably be specific about this, one way or the other.