* src/eval.c (parse_expr): Allow for missing primary between ? and :.
* doc/m4.texi (eval): Document this.
---
I have finished forward-porting everything from branch-1.4 into
branch-1.6. In the process, I also added this patch.
branch-1.6 already added the a?b:c operator long ago, but this patch
improves it to support a?:c like gcc.
doc/m4.texi | 7 +++++--
src/eval.c | 16 +++++++++++++++-
2 files changed, 20 insertions(+), 3 deletions(-)
diff --git a/doc/m4.texi b/doc/m4.texi
index 84f84f96..10314d42 100644
--- a/doc/m4.texi
+++ b/doc/m4.texi
@@ -6978,8 +6978,9 @@ Eval
As a GNU extension, the operator @samp{**} performs integral
exponentiation. The operator is right-associative, and if evaluated,
the exponent must be non-negative, and at least one of the arguments
-must be non-zero, or a warning is issued. Also, the C operator
-@samp{?:} is supported.
+must be non-zero, or a warning is issued. Also, the ternary C operator
+@samp{?:} is supported, including the GNU extension of reusing the
+non-zero value of the left side if the middle term is empty.
@example
eval(`2 ** 3 ** 2')
@@ -7009,6 +7010,8 @@ Eval
eval(`1/0 ? 2 : 3')
@error{}m4:stdin:12: warning: eval: divide by zero: '1/0 ? 2 : 3'
@result{}
+eval(`2 ?: 3')
+@result{}2
@end example
Within @var{expression}, (but not @var{radix} or @var{width}), numbers
diff --git a/src/eval.c b/src/eval.c
index 67b5ce85..bd10e250 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -393,7 +393,21 @@ parse_expr (int32_t *v1, eval_error er, unsigned min_prec)
et = eval_lex (&v2);
while (et / 10 >= min_prec)
{
- if ((er2 = primary (&v2)) >= SYNTAX_ERROR)
+ if (et == QUESTION)
+ {
+ et2 = eval_lex (&v2);
+ eval_undo ();
+ if (et2 == COLON)
+ {
+ v2 = *v1;
+ er2 = er;
+ }
+ else
+ er2 = primary (&v2);
+ }
+ else
+ er2 = primary (&v2);
+ if (er2 >= SYNTAX_ERROR)
return er2;
et2 = eval_lex (&v3);
/* Handle binary operators of higher precedence or right-associativity */
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--
2.49.0
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