+2000-10-12 Akim Demaille <akim@epita.fr>
+
+ Diagnose AC_REQUIRE circular dependencies.
+
+ * acgeneral.m4 (_AC_DEFUN_PRO, _AC_DEFUN_EPI): Keep a stack of
+ macro expansions, _AC_EXPANSION_STACK.
+ Use `_AC_EXPANDING(FOO)' to record the fact that `FOO' is being
+ expanded.
+ (_AC_REQUIRE): Diagnose required macros which are already being
+ expanded.
+ Record in _AC_EXPANSION_STACK the AC_REQUIRE calls.
+ (_AC_EXPANSION_STACK_DUMP): New macro.
+
2000-10-12 Akim Demaille <akim@epita.fr>
* libm4.m4 (m4_dumpdefs, _m4_dumpdefs_up, _m4_dumpdefs_down): New
* Autoconf 2.50
+** More tests
+Check that AC_REQUIRE circular dependencies are caught.
+
+** _AC_EXPANSION_STACK_DUMP
+Where ever AC_FATAL is used, we should call _AC_EXPANSION_STACK_DUMP.
+Try to see if we can use __FILE__ and __LINE__ in the stack: this
+would provide much more accurate error messages (but it might be
+costly...).
+
** --target & AC_ARG_PROGRAM
Shouldn't *any* `program' be installed as `$target_alias-program' even
if AC_ARG_PROGRAM is not called? That would be much more predictable.
# needed machinery for `AC_REQUIRE'. A macro must be AC_DEFUN'd if
# either it is AC_REQUIRE'd, or it AC_REQUIRE's.
#
+# Two things deserve attention and are detailed below:
+# 1. Implementation of AC_REQUIRE
+# 2. Keeping tracking of the expansion stack
+#
+# 1. Implementation of AC_REQUIRE
+# ===============================
+#
# Of course AC_DEFUN AC_PROVIDE's the macro, so that a macro which has
# been expanded is not expanded again when AC_REQUIRE'd, but the
# difficult part is the proper expansion of macros when they are
# DUMP: undefined
# BODY: TEST2a; TEST3; TEST2b; TEST1
# diversions: BODY |-
+#
+#
+# 2. Keeping tracking of the expansion stack
+# ==========================================
+#
+# When M4 expansion goes wrong it is often extremely hard to find the
+# path amongst macros that drove to the failure. What is needed case
+# is the stack of macro `calls'. One could imagine that GNU M4 would
+# maintain a stack of macro expansion, unfortunately it doesn't, so we
+# do it by hand. This is of course extremely costly, but the help
+# this stack provides is worth it. Nevertheless to limit the
+# performance penalty this is implemented only for AC_DEFUN'd macros,
+# not for define'd macros.
+#
+# The scheme is simplistic: each time we enter an AC_DEFUN'd macros,
+# we pushdef its name in _AC_EXPANSION_STACK, and when we exit the
+# macro, we popdef _AC_EXPANSION_STACK.
+#
+# In addition, we want to use the expansion stack to detect circular
+# AC_REQUIRE dependencies. This means we need to browse the stack to
+# check whether a macro being expanded is AC_REQUIRE'd. For ease of
+# implementation, and certainly for the benefit of performances, we
+# don't browse the _AC_EXPANSION_STACK, rather each time we expand a
+# macro FOO we define _AC_EXPANDING(FOO). Then AC_REQUIRE(BAR) simply
+# needs to check whether _AC_EXPANDING(BAR) is defined to diagnose a
+# circular dependency.
+#
+# To improve the diagnostic, in addition to keeping track of the stack
+# of macro calls, _AC_EXPANSION_STACK also records the AC_REQUIRE
+# stack. Note that therefore an AC_DEFUN'd macro being required will
+# appear twice in the stack: the first time because it is required,
+# the second because it is expanded. We can avoid this, but it has
+# two small drawbacks: (i) the implementation is slightly more
+# complex, and (ii) it hides the difference between define'd macros
+# (which don't appear in _AC_EXPANSION_STACK) and AC_DEFUN'd macros
+# (which do). The more debugging information, the better.
+
+
+# _AC_EXPANSION_STACK_DUMP
+# ------------------------
+# Dump the expansion stack.
+define([_AC_EXPANSION_STACK_DUMP],
+[ifdef([_AC_EXPANSION_STACK],
+ [m4_errprint([ ]defn([_AC_EXPANSION_STACK]))dnl
+popdef([_AC_EXPANSION_STACK])dnl
+_AC_EXPANSION_STACK_DUMP()],
+ [m4_errprint([ the top level])])])
# _AC_DEFUN_PRO(MACRO-NAME)
# The prologue for Autoconf macros.
define([_AC_DEFUN_PRO],
[AC_PROVIDE([$1])dnl
+pushdef([_AC_EXPANSION_STACK], [$1 is expanded from...])dnl
+pushdef([_AC_EXPANDING($1)])dnl
ifdef([_AC_DIVERT_DUMP],
[AC_DIVERT_PUSH(defn([_AC_DIVERT_DIVERSION]))],
[define([_AC_DIVERT_DUMP], defn([_AC_DIVERT_DIVERSION]))dnl
ifelse(_AC_DIVERT_DUMP, _AC_DIVERT_DIVERSION,
[undivert(_AC_DIVERT([PREPARE]))dnl
undefine([_AC_DIVERT_DUMP])])dnl
+popdef([_AC_EXPANSION_STACK])dnl
+popdef([_AC_EXPANDING($1)])dnl
])
# AC_DEFUN(NAME, EXPANSION)
# -------------------------
-#
# Define a macro which automatically provides itself. Add machinery
# so the macro automatically switches expansion to the diversion
# stack if it is not already using it. In this case, once finished,
# ------------------------------------------
# If NAME-TO-CHECK has never been expanded (actually, if it is not
# AC_PROVIDE'd), expand BODY-TO-EXPAND *before* the current macro
-# expansion. Once expanded, emit it in _AC_DIVERT_DUMP.
+# expansion. Once expanded, emit it in _AC_DIVERT_DUMP. Keep track
+# of the AC_REQUIRE chain in _AC_EXPANSION_STACK.
#
# The normal cases are:
#
# `extension' prevents `AC_LANG_COMPILER' from having actual arguments that
# it passes to `AC_LANG_COMPILER(C)'.
define([_AC_REQUIRE],
-[ifndef([_AC_DIVERT_DUMP],
- [AC_FATAL([$0: cannot be used outside of an AC_DEFUN'd macro])])dnl
+[pushdef([_AC_EXPANSION_STACK],
+ [$1 is required by...])dnl
+ifdef([_AC_EXPANDING($1)],
+ [m4_errprint([AC_REQUIRE: circular dependency of $1])dnl
+_AC_EXPANSION_STACK_DUMP()dnl
+m4exit(1)])dnl
+ifndef([_AC_DIVERT_DUMP],
+ [AC_FATAL([AC_REQUIRE: cannot be used outside of an AC_DEFUN'd macro])])dnl
AC_PROVIDE_IFELSE([$1],
[],
[AC_DIVERT_PUSH(m4_eval(_AC_DIVERT_DIVERSION - 1))dnl
[],
[AC_DIAGNOSE([syntax],
[$1 is AC_REQUIRE'd but is not AC_DEFUN'd])])dnl
+popdef([_AC_EXPANSION_STACK])dnl
])
# AC_PROVIDE(MACRO-NAME)
# ----------------------
+# Ideally we should use `AC_PROVIDE($1)', but unfortunately many third
+# party macros know that we use `AC_PROVIDE_$1' and they depend on it.
define([AC_PROVIDE],
[define([AC_PROVIDE_$1])])
# needed machinery for `AC_REQUIRE'. A macro must be AC_DEFUN'd if
# either it is AC_REQUIRE'd, or it AC_REQUIRE's.
#
+# Two things deserve attention and are detailed below:
+# 1. Implementation of AC_REQUIRE
+# 2. Keeping tracking of the expansion stack
+#
+# 1. Implementation of AC_REQUIRE
+# ===============================
+#
# Of course AC_DEFUN AC_PROVIDE's the macro, so that a macro which has
# been expanded is not expanded again when AC_REQUIRE'd, but the
# difficult part is the proper expansion of macros when they are
# DUMP: undefined
# BODY: TEST2a; TEST3; TEST2b; TEST1
# diversions: BODY |-
+#
+#
+# 2. Keeping tracking of the expansion stack
+# ==========================================
+#
+# When M4 expansion goes wrong it is often extremely hard to find the
+# path amongst macros that drove to the failure. What is needed case
+# is the stack of macro `calls'. One could imagine that GNU M4 would
+# maintain a stack of macro expansion, unfortunately it doesn't, so we
+# do it by hand. This is of course extremely costly, but the help
+# this stack provides is worth it. Nevertheless to limit the
+# performance penalty this is implemented only for AC_DEFUN'd macros,
+# not for define'd macros.
+#
+# The scheme is simplistic: each time we enter an AC_DEFUN'd macros,
+# we pushdef its name in _AC_EXPANSION_STACK, and when we exit the
+# macro, we popdef _AC_EXPANSION_STACK.
+#
+# In addition, we want to use the expansion stack to detect circular
+# AC_REQUIRE dependencies. This means we need to browse the stack to
+# check whether a macro being expanded is AC_REQUIRE'd. For ease of
+# implementation, and certainly for the benefit of performances, we
+# don't browse the _AC_EXPANSION_STACK, rather each time we expand a
+# macro FOO we define _AC_EXPANDING(FOO). Then AC_REQUIRE(BAR) simply
+# needs to check whether _AC_EXPANDING(BAR) is defined to diagnose a
+# circular dependency.
+#
+# To improve the diagnostic, in addition to keeping track of the stack
+# of macro calls, _AC_EXPANSION_STACK also records the AC_REQUIRE
+# stack. Note that therefore an AC_DEFUN'd macro being required will
+# appear twice in the stack: the first time because it is required,
+# the second because it is expanded. We can avoid this, but it has
+# two small drawbacks: (i) the implementation is slightly more
+# complex, and (ii) it hides the difference between define'd macros
+# (which don't appear in _AC_EXPANSION_STACK) and AC_DEFUN'd macros
+# (which do). The more debugging information, the better.
+
+
+# _AC_EXPANSION_STACK_DUMP
+# ------------------------
+# Dump the expansion stack.
+define([_AC_EXPANSION_STACK_DUMP],
+[ifdef([_AC_EXPANSION_STACK],
+ [m4_errprint([ ]defn([_AC_EXPANSION_STACK]))dnl
+popdef([_AC_EXPANSION_STACK])dnl
+_AC_EXPANSION_STACK_DUMP()],
+ [m4_errprint([ the top level])])])
# _AC_DEFUN_PRO(MACRO-NAME)
# The prologue for Autoconf macros.
define([_AC_DEFUN_PRO],
[AC_PROVIDE([$1])dnl
+pushdef([_AC_EXPANSION_STACK], [$1 is expanded from...])dnl
+pushdef([_AC_EXPANDING($1)])dnl
ifdef([_AC_DIVERT_DUMP],
[AC_DIVERT_PUSH(defn([_AC_DIVERT_DIVERSION]))],
[define([_AC_DIVERT_DUMP], defn([_AC_DIVERT_DIVERSION]))dnl
ifelse(_AC_DIVERT_DUMP, _AC_DIVERT_DIVERSION,
[undivert(_AC_DIVERT([PREPARE]))dnl
undefine([_AC_DIVERT_DUMP])])dnl
+popdef([_AC_EXPANSION_STACK])dnl
+popdef([_AC_EXPANDING($1)])dnl
])
# AC_DEFUN(NAME, EXPANSION)
# -------------------------
-#
# Define a macro which automatically provides itself. Add machinery
# so the macro automatically switches expansion to the diversion
# stack if it is not already using it. In this case, once finished,
# ------------------------------------------
# If NAME-TO-CHECK has never been expanded (actually, if it is not
# AC_PROVIDE'd), expand BODY-TO-EXPAND *before* the current macro
-# expansion. Once expanded, emit it in _AC_DIVERT_DUMP.
+# expansion. Once expanded, emit it in _AC_DIVERT_DUMP. Keep track
+# of the AC_REQUIRE chain in _AC_EXPANSION_STACK.
#
# The normal cases are:
#
# `extension' prevents `AC_LANG_COMPILER' from having actual arguments that
# it passes to `AC_LANG_COMPILER(C)'.
define([_AC_REQUIRE],
-[ifndef([_AC_DIVERT_DUMP],
- [AC_FATAL([$0: cannot be used outside of an AC_DEFUN'd macro])])dnl
+[pushdef([_AC_EXPANSION_STACK],
+ [$1 is required by...])dnl
+ifdef([_AC_EXPANDING($1)],
+ [m4_errprint([AC_REQUIRE: circular dependency of $1])dnl
+_AC_EXPANSION_STACK_DUMP()dnl
+m4exit(1)])dnl
+ifndef([_AC_DIVERT_DUMP],
+ [AC_FATAL([AC_REQUIRE: cannot be used outside of an AC_DEFUN'd macro])])dnl
AC_PROVIDE_IFELSE([$1],
[],
[AC_DIVERT_PUSH(m4_eval(_AC_DIVERT_DIVERSION - 1))dnl
[],
[AC_DIAGNOSE([syntax],
[$1 is AC_REQUIRE'd but is not AC_DEFUN'd])])dnl
+popdef([_AC_EXPANSION_STACK])dnl
])
# AC_PROVIDE(MACRO-NAME)
# ----------------------
+# Ideally we should use `AC_PROVIDE($1)', but unfortunately many third
+# party macros know that we use `AC_PROVIDE_$1' and they depend on it.
define([AC_PROVIDE],
[define([AC_PROVIDE_$1])])
projects / thirdparty / autoconf.git / commitdiff
