build: Fix M4sh/Autoconf coding style

Indent the code in a way that makes it easier to follow. Use AS_IF
instead of shell constructs. Quote all autoconf macro arguments.

Add a new section to coding-style.txt describing M4sh/Autoconf.

1 files changed, 54 insertions, 0 deletions

diff --git a/doc/coding-style.txt b/doc/coding-style.txt
index 06bf3b792..0e07806e4 100644
--- a/doc/coding-style.txt
+++ b/doc/coding-style.txt
@@ -14,6 +14,60 @@ Every new feature, option or behavior change needs to be documented with
 the version introducing the change.
 
 
+Dpkg M4sh/Autoconf coding style 1016-09-05
+===============================
+
+General
+~~~~~~~
+
+All dpkg specific macros need to be prefixed with «DPKG_». Complex checks
+should be defined as new macros under m4/dpkg-<name>.m4, and those used
+in configure.ac which should look pretty simple.
+
+Quoting and indentation
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Code and arguments that wrap into the next line are indented by two spaces.
+
+In principle all macro argument should always be quoted. Which gives brings
+one of the biggest readability issues with M4sh/Autoconf code, the amount of
+consecutive quotes and parenthesis pairs, which can make it very hard to
+notice if they are unbalanced. To avoid this we use a style that tries to
+avoid more than two consecutive blocks of «])».
+
+We can either use a style resembling very simple function calls, when the
+arguments are as well very simple, such as:
+
+  AC_DEFINE_UNQUOTED([SOME_VARIABLE],
+    [SOME_CONCOCTED_WAY_TO_GET_A_VALUE],
+    [Some descriptive text here])
+
+  AS_CASE([condition],
+    [case-a], [do-a],
+    [case-b], [do-b])
+
+Or one resembling curly-braced C-style blocks, such as this:
+
+  AS_IF([condition], [
+    DO_SOMETHING([here])
+  ], [
+    DO_OTHERWISE([there])
+  ])
+
+Except for AC_ARG_WITH, AC_ARG_ENABLE and AM_CONDITIONAL which need their
+second argument quoted tightly surrounding the code, like this:
+
+  AC_ARG_ENABLE([feature],
+    [AS_HELP_STRING([--disable-feature], [Disable feature])],
+    [], [enable_feature="yes"])
+
+  AM_CONDITIONAL([HAVE_SOME_FEATURE],
+    [test "x$ac_cv_have_some_feature" = "xyes" && \
+     test "x$ac_cv_have_some_feature" = "xyes"])
+
+or the output will get messed up.
+
+
 Dpkg C/C++ coding style 2016-01-29
 =======================