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\begin_document
\begin_header
\textclass literate-article
\begin_preamble
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\language english
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\end_header

\begin_body

\begin_layout Title

LyX listerrors:
\newline
rewritten in Python
\end_layout

\begin_layout Author

Kayvan A.
 Sylvan
\newline

\begin_inset LatexCommand \url{mailto:kayvan@sylvan.com}

\end_inset


\end_layout

\begin_layout Date

3/15/2002
\end_layout

\begin_layout Abstract

The listerrors program used to be compiled as a C program and installed
 as 
\emph on
BINDIR/listerrors
\emph default
 along with LyX in order to perform some simple re-formatting of noweb and
 GCC error messages.
 This document describes and implements the Python version of the same program.
\end_layout

\begin_layout Standard


\begin_inset LatexCommand \tableofcontents{}

\end_inset


\end_layout

\begin_layout Section

Introduction
\end_layout

\begin_layout Standard

The motivation for this program was Bugzilla bug 190
\begin_inset Foot
status collapsed

\begin_layout Standard

Visit 
\begin_inset LatexCommand \url{http://bugzilla.lyx.org/show_bug.cgi?id=190}

\end_inset

 for the details.
\end_layout

\end_inset

 dealing with the 
\begin_inset Quotes eld
\end_inset

listerrors
\begin_inset Quotes erd
\end_inset

 executable.
\end_layout

\begin_layout Standard

What is 
\begin_inset Quotes eld
\end_inset

listerrors
\begin_inset Quotes erd
\end_inset

? Usually, LyX has great support for parsing of error messages.
 For each error in the log file, LyX pops up an error box at that location
 in the LyX window.
 The error scanning routines expect these errors to be in a certain format
 (similar to LaTeX errors).
 When dealing with Literate Programs, you have 
\begin_inset Quotes eld
\end_inset

noweb
\begin_inset Foot
status collapsed

\begin_layout Standard

See 
\begin_inset LatexCommand \url{http://www.eecs.harvard.edu/~nr/noweb}

\end_inset

 for more information about noweb.
\end_layout

\end_inset


\begin_inset Quotes erd
\end_inset

 as well as gcc error messages (and potentially others).
 The listerrors program attempts to standardize these error messages to
 a format that LyX can parse and react to.
\end_layout

\begin_layout Standard

In a nutshell, the problems with the old implementation of listerrors that
 bug 190 refers to were::
\end_layout

\begin_layout Enumerate

It was a C program and it was installed in the user path in the same directory
 as LyX.
 Having such a generically named binary in, for example, 
\emph on
/usr/bin
\emph default
, was potentially confusing.
\end_layout

\begin_layout Enumerate

It required that noweb be installed on the compiling machine (the source
 was extracted by noweb from 
\emph on
SRCDIR/examples/Literate.lyx
\emph default
, compiled and installed by 
\begin_inset Quotes eld
\end_inset

make install
\begin_inset Quotes erd
\end_inset

).
\end_layout

\begin_layout Standard

The new version deals with these problems in the following fashion:
\end_layout

\begin_layout Enumerate

Both the example file (this document) and the program are to be added to
 the LyX CVS repository.
\end_layout

\begin_layout Enumerate

The program itself will be installed in 
\emph on
SHAREDIR/lyx/scripts
\emph default
, along with other LyX-specific helper scripts.
\end_layout

\begin_layout Standard

In the design and implementation of this new 
\begin_inset Quotes eld
\end_inset

listerrors
\begin_inset Quotes erd
\end_inset

, the Python
\begin_inset Foot
status collapsed

\begin_layout Standard

See the Python home page (
\begin_inset LatexCommand \url{http://www.python.org}

\end_inset

) for more information.
\end_layout

\end_inset

 language was chosen since it is fully multi-platform and provides a very
 uniform and easy to read syntax.
 This re-write also simplifies the code for 
\begin_inset Quotes eld
\end_inset

listerrors
\begin_inset Quotes erd
\end_inset

 greatly.
 Python is installed by default on all modern Linux systems and is freely
 available for all other platforms.
\end_layout

\begin_layout Scrap

<<listerrors>>=
\newline
#!/usr/bin/python
\newline
"""reformat noweb and compiler errors for LyX.
\newline

\newline
Expects to read from stdin and output to stdout.
\newline
"""
\newline

\newline
__author__ = "Kayvan A.
 Sylvan <kayvan@sylvan.com>"
\newline
__date__ = "$Date: 2005/07/18 09:42:26 $"
\newline
__version__ = "$Revision: 1.5 $"
\newline
__credits__ = """Edmar Wienskoski Jr.
 <edmar-w-jr@technologist.com>
\newline
    original Literate support for LyX.
\newline
Bernard Michael Hurley <berhardh@westherts.ac.uk>
\newline
    modifications to original listerrors."""
\newline
__copyright__ = "Copyright 2002 - Kayvan Sylvan."
\newline

\newline
import sys, string
\newline

\newline
<<Function Bodies>>
\newline

\newline
if __name__ == "__main__":
\newline
  main()
\newline
@
\end_layout

\begin_layout Section

LaTeX style error message
\end_layout

\begin_layout Standard

The following function mimics the TeX error message format.
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
def write_error(msg, tool = "noweb", line_number = 1):
\newline
  """Write out the given message in TeX error style.
\newline

\newline
  called like: write_error(msg, tool, line_number)."""
\newline
  print "! Build Error: ==> %s ==>
\backslash
n" % (tool),
\newline
  print " ...
\backslash
n
\backslash
nl.%d ...
\backslash
n" % (line_number),
\newline
  if type(msg) == type("str"): # simple string
\newline
    print msg
\newline
  else: # some kind of list (sequence or tuple)
\newline
    for m in msg:
\newline
        if m != "": print m,
\newline
    print
\newline

\newline
@ %def write_error
\end_layout

\begin_layout Section

Filtering errors
\end_layout

\begin_layout Standard

The only complication in our filtering code is that some parsers might need
 to push back lines that are read in to be read again later.
 We solve this problem by implementing a 
\begin_inset Quotes eld
\end_inset

getline
\begin_inset Quotes erd
\end_inset

 and 
\begin_inset Quotes eld
\end_inset

pushline
\begin_inset Quotes erd
\end_inset

 set of functions:
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
__lines = [] # lines pushed back
\newline

\newline
def getline(file = sys.stdin):
\newline
  """read a line from internal stack or from file.
\newline

\newline
  optional file argument defaults to sys.stdin."""
\newline
  global __lines
\newline
  lines = __lines
\newline
  if lines:
\newline
    line = lines.pop()
\newline
  else:
\newline
    line = file.readline()
\newline
  return line
\newline

\newline
@ %def getline
\end_layout

\begin_layout Standard

And now for the corresponding pushline function:
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
def pushline(line):
\newline
  "push a line onto the pushback stack."
\newline
  global __lines
\newline
  lines = __lines
\newline
  lines.append(line)
\newline

\newline
@ %def pushline
\end_layout

\begin_layout Standard

The main() entry point function is extremely simple.
 Note that this version of 
\begin_inset Quotes eld
\end_inset

listerrors
\begin_inset Quotes erd
\end_inset

 takes no options and simply filters, attempting simply to match against
 the known error message patterns.
 The listerrors C program handled a single-character command-line argument
 that the current code no longer needs.
 
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
def main():
\newline
  """Entry point for listerrors.
 Takes no options.
\newline

\newline
  Reads stdin and writes to stdout.
 Filter errors"""
\newline

\newline
  while 1:
\newline
    line = getline()
\newline
    if line == "": break
\newline
    <<Check line against patterns and take action>>
\newline
@ %def main
\end_layout

\begin_layout Standard

For each line read in, we need to find out if it matches any of our tools
 (noweb, gcc, etc.) and act accordingly.
\end_layout

\begin_layout Scrap

<<Check line against patterns and take action>>=
\newline
try_patterns_dispatch = [ noweb_try, gcc_try, xlc_try ]
\newline
for predicate in try_patterns_dispatch:
\newline
  if predicate(line): break
\newline
@
\end_layout

\begin_layout Section

Different Error Formats
\end_layout

\begin_layout Standard

The following sections handle the various error message formats that we
 recognize in this program.
 
\end_layout

\begin_layout Subsection

noweb errors
\end_layout

\begin_layout Standard

Noweb errors are output on a single line, so examining just the current
 line is enough.
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
def noweb_try(line):
\newline
  """see if line is a noweb error.
\newline

\newline
  Returns 1 on success, 0 otherwise.
 Outputs on stdout."""
\newline
  retval = 0
\newline
  <<Look for the unescaped angle-brackets in documentation>>
\newline
  <<Look for anything with double angle brackets>>
\newline
  <<Last ditch effort scan for specific strings>>
\newline
  return retval
\newline

\newline
@ %def noweb_try
\end_layout

\begin_layout Standard

First, we look for the 
\begin_inset Quotes eld
\end_inset

unescaped < < in documentation chunk
\begin_inset Quotes erd
\end_inset

 message.
 This is the only message with an associated line number from noweb.
\end_layout

\begin_layout Scrap

<<Look for the unescaped angle-brackets in documentation>>=
\newline
if string.find(line, ": unescaped << in documentation chunk") != -1:
\newline
  line_parts = string.split(line, ':')
\newline
  num_str = line_parts[1]
\newline
  num_len = len(num_str)
\newline
  i = 0
\newline
  while i < num_len and (num_str[i] in string.digits): i = i + 1
\newline
  if i == num_len:
\newline
    write_error(":" + line_parts[2], "noweb", int(num_str))
\newline
    retval = 1
\newline
@
\end_layout

\begin_layout Standard

Some noweb messages are simply about undefined scraps.
 These can be seen by looking for matching double-angle-brackets.
\end_layout

\begin_layout Scrap

<<Look for anything with double angle brackets>>=
\newline
if (not retval):
\newline
  left = string.find(line, "<<")
\newline
  if (left != -1) and ((left + 2) < len(line)) and 
\backslash

\newline
     (string.find(line[left+2:], ">>") != -1):
\newline
    write_error(line, "noweb");
\newline
    retval = 1;
\newline
@
\end_layout

\begin_layout Standard

Finally, here is an additional list of explicit strings to check for.
\end_layout

\begin_layout Scrap

<<Last ditch effort scan for specific strings>>=
\newline
if (not retval):
\newline
  msgs_to_try = ("couldn't open file",
\newline
    "couldn't open temporary file",
\newline
    "error writing temporary file",
\newline
    "ill-formed option",
\newline
    "unknown option",
\newline
    "Bad format sequence",
\newline
    "Can't open output file",
\newline
    "Can't open temporary file",
\newline
    "Capacity exceeded:",
\newline
    "Ignoring unknown option -",
\newline
    "This can't happen:",
\newline
    "non-numeric line number in")
\newline
  for msg in msgs_to_try:
\newline
    if string.find(line, msg) != -1:
\newline
      write_error(line, "noweb")
\newline
      retval = 1
\newline
      break
\newline
@
\end_layout

\begin_layout Subsection

gcc errors
\end_layout

\begin_layout Standard

The gcc errors can be multi-line, with the following format:
\end_layout

\begin_layout LyX-Code

foo.c: In function `main': 
\newline
foo.c:3: `bar' undeclared (first use in this function) 
\newline
foo.c:3: (Each undeclared identifier is reported only once 
\newline
foo.c:3: for each function it appears in.) 
\newline
foo.c:3: parse error before `x'
\end_layout

\begin_layout Standard

In order to parse this, the gcc error handler has to look ahead and return
 any and all lines that do not match the expected pattern.
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
def gcc_try(line):
\newline
  """See if line is a gcc error.
 Read ahead to handle all the lines.
\newline

\newline
  Returns 1 on success, 0 otherwise.
 Outputs on stdout."""
\newline
  retval = 0
\newline
  <<Handle the gcc error message>>
\newline
  return retval
\newline

\newline
@ %def gcc_try
\end_layout

\begin_layout Standard

The error message starts with a gcc header (as above) without an associated
 line number.
\end_layout

\begin_layout Scrap

<<Handle the gcc error message>>= 
\newline
first_space = string.find(line, ' ')
\newline
if first_space > 1: # The smallest would be "X: "
\newline
  if line[first_space - 1] == ':':
\newline
    header_to_see = line[:first_space - 1]
\newline
    next_line = getline()
\newline
    if next_line and next_line[:first_space - 1] == header_to_see:
\newline
      num_end = first_space
\newline
      while next_line[num_end] in string.digits: num_end = num_end + 1
\newline
      if num_end > first_space: # good!
\newline
        <<Accumulate gcc error lines and print it>>
\newline
      else: # oops! Not a gcc error.
\newline
        pushline(next_line)
\newline
    elif next_line:
\newline
      pushline(next_line) # return this line to input stream
\newline
@
\end_layout

\begin_layout Standard

At the point in the code that we know that we are in the middle of an error
 message, we do the following:
\end_layout

\begin_layout Scrap

<<Accumulate gcc error lines and print it>>=
\newline
num_str = next_line[first_space:num_end]
\newline
msgs = [line[first_space:]]
\newline
msgs.append(next_line[num_end + 1:])
\newline
header_to_see = next_line[:num_end]
\newline
next_line = getline()
\newline
while next_line and next_line[:num_end] == header_to_see:
\newline
  msgs.append(next_line[num_end + 1:])
\newline
  next_line = getline()
\newline
if next_line: pushline(next_line)
\newline
write_error(msgs, "gcc", int(num_str))
\newline
retval = 1
\newline
@
\end_layout

\begin_layout Subsection

xlc errors
\end_layout

\begin_layout Standard

A xlc error message is easy to identify.
 Every error message starts with a quoted string with no spaces, a comma,
 a space, the word 
\begin_inset Quotes eld
\end_inset

line
\begin_inset Quotes erd
\end_inset

, a space, and some variable text.
 The following routine tests if a given buffer line matches this criteria
 (this code would probably be simpler if I used the 
\begin_inset Quotes eld
\end_inset

re
\begin_inset Quotes erd
\end_inset

 regexp module, but we don't really need the full regular expression engine
 here).
 
\end_layout

\begin_layout Scrap

<<Function Bodies>>=
\newline
def xlc_try(line):
\newline
  """see if line is an xlc error.
\newline

\newline
  Returns 1 on success, 0 otherwise.
 Outputs on stdout."""
\newline
  retval = 0
\newline
  if line[0] == '"': # This is the first character of all xlc errors
\newline
    next_quote = string.find(line, '"', 1)
\newline
    first_space = string.find(line, ' ')
\newline
    if (next_quote != -1) and (first_space > next_quote): # no space inisde
 quotes
\newline
      if line[first_space - 1:first_space + 6] == ", line ":
\newline
        num_start = num_end = first_space + 6
\newline
        while line[num_end] in string.digits: num_end = num_end + 1
\newline
        if num_end > num_start:
\newline
          write_error(line, "xlc", int(line[num_start : num_end]))
\newline
          retval = 1
\newline
  return retval
\newline
  
\newline
@ %def xlc_try
\end_layout

\begin_layout Section

Extracting the code
\end_layout

\begin_layout Standard

This project can be tangled from LyX if you set your 
\begin_inset Quotes eld
\end_inset

Program
\begin_inset Quotes erd
\end_inset

 convertor to call a generic script that always extracts a scrap named 
\family typewriter
build-script
\family default
 and executes it.
 Here is an example of such a generic script:
\end_layout

\begin_layout LyX-Code

#!/bin/sh
\newline
notangle -Rbuild-script $1 | env NOWEB_SOURCE=$1 sh
\end_layout

\begin_layout Standard

This section defines our build-script, which extracts the code.
\end_layout

\begin_layout Scrap

<<build-script>>=
\newline
#!/bin/sh
\newline
if [ -z "$NOWEB_SOURCE" ]; then NOWEB_SOURCE=listerrors.nw; fi
\newline
notangle -Rlisterrors ${NOWEB_SOURCE} > listerrors
\newline
chmod +x listerrors
\newline
@
\end_layout

\begin_layout Section

Indices
\end_layout

\begin_layout Standard

This section provides cross-references into the rest of the program.
\end_layout

\begin_layout Subsection

Macros
\end_layout

\begin_layout Standard


\begin_inset ERT
status collapsed

\begin_layout Standard

\backslash
nowebchunks
\end_layout

\end_inset


\end_layout

\begin_layout Subsection

Identifiers
\end_layout

\begin_layout Standard


\begin_inset ERT
status collapsed

\begin_layout Standard

\backslash
nowebindex
\end_layout

\end_inset


\end_layout

\end_body
\end_document
