[PATCH] parseheredoc: fix alias expansion: save and restore checkkwd

[Martijn Dekker <martijn@inlv.org>]

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Op 25-01-20 om 02:38 schreef Harald van Dijk:
> On 25/01/2020 01:13, Harald van Dijk wrote:
>> On 24/01/2020 23:48, Martijn Dekker wrote:
>>> There is a regression involving alias expansion, a here-document, and 
>>> a command substitution. The following worked fine until dash 0.5.8; 
>>> it throws a syntax error as of dash 0.5.9.
>>>
>>> alias BEGIN='{' END='}'
>>> BEGIN
>>> cat <<eof
>>> $(echo hi)
>>> eof
>>> END
>>
>> Nice find.
>>
>> When the newline after cat <<eof is seen, checkkwd is changed to 
>> indicate that the shell is in a state where aliases can be expanded. 
>> Then, parseheredoc() is called, which in turn calls readtoken1() to 
>> parse the here-document. readtoken() re-sets checkkwd once it is done, 
>> but readtoken1() does not, so normally this preserves the "can expand 
>> aliases" state. However, nested command substitutions do reset 
>> checkkwd, so things break.
>>
>> Until 0.5.8, parseheredoc() was called first, and only after that did 
>> checkkwd get changed.
>>
>> Either parseheredoc() needs to save and restore checkkwd, or the code 
>> calling parseheredoc() needs to ensure that it sets checkkwd as 
>> appropriate afterwards.

Saving and restoring checkkwd in parseheredoc() seems the simplest and 
the most future-proof, so here's a patch to do that.

> There is another place that parseheredoc() can be called from where 
> checkkwd was not being corrected afterwards:
> 
>    alias BEGIN='{' END='}'
>    : <<EOF &&
>    $(echo hi)
>    EOF
>    BEGIN
>    echo ok
>    END
> 
> This has been failing for longer.

The patch fixes this as well.

-- 
modernish -- harness the shell
https://github.com/modernish/modernish

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diff --git a/src/parser.c b/src/parser.c
index b318b08..8840262 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -661,6 +661,7 @@ parsefname(void)
 STATIC void
 parseheredoc(void)
 {
+	int savecheckkwd = checkkwd;
 	struct heredoc *here;
 	union node *n;
 
@@ -683,6 +684,8 @@ parseheredoc(void)
 		here->here->nhere.doc = n;
 		here = here->next;
 	}
+
+	checkkwd = savecheckkwd;
 }
 
 STATIC int