m4: Improved fatal_error
17.8 Solution for 'fatal_error'
===============================
The 'fatal_error' macro (⇒M4exit) is not robust to versions of
GNU M4 earlier than 1.4.8, where invoking '__file__' (⇒Location)
inside 'm4wrap' would result in an empty string, and '__line__' resulted
in '0' even though all files start at line 1. Furthermore, versions
earlier than 1.4.6 did not support the '__program__' macro. If you want
'fatal_error' to work across the entire 1.4.x release series, a better
implementation would be:
define(`fatal_error',
`errprint(ifdef(`__program__', `__program__', ``m4'')'dnl
`:ifelse(__line__, `0', `',
`__file__:__line__:')` fatal error: $*
')m4exit(`1')')
=>
m4wrap(`divnum(`demo of internal message')
fatal_error(`inside wrapped text')')
=>
^D
error->m4:stdin:6: Warning: excess arguments to builtin `divnum' ignored
=>0
error->m4:stdin:6: fatal error: inside wrapped text
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