Another alias substitution bug, now involving case statements

Another alias substitution bug, now involving case statements

[Harald van Dijk]

Hi,

Checking alias substitution handling in more detail after Martijn 
Dekker's report, I found another case where I believe dash's behaviour 
is incorrect. First, please consider this test:

   alias a="case x in " b=x
   a b) echo hi ;; esac

bash, ksh and pdksh never check whether a case pattern is a valid alias 
name, so they print nothing.

bosh, dash, mksh, yash and zsh do allow the space at the end of a's 
definition to cause b to be considered as an alias name.

Based on the literal text of the current standard, I believe 
bash/ksh/pdksh's behaviour is correct. Based on accepted new wording for 
the standard, new wording that was drafted without considering this 
special case, I believe the bosh/dash/mksh/yash/zsh behaviour is 
correct. I would not at this time consider this a bug in any of the shells.

Now, consider this modified version:

   alias a="case x in " b=x
   a
   b) echo hi ;; esac

Here, the next token after "a" is a newline token, not b. Here, b must 
definitely not be considered as an alias name. bosh, dash, mksh and zsh 
do perform alias substitution anyway, yash does not.

The problem here is in the "eat newlines" behaviour of readtoken(). 
There are two reasons why CHKALIAS might be set. It might be set because 
the parser is in a state where the next token could be the start of a 
simple command, or it might be set because the parser processed a blank 
at the end of a prior alias definition. In the first case, after eating 
a newline, the parser is still in a state where the next token could be 
the start of a simple command, so CHKALIAS should not be dropped. In the 
second case, the blank should only affect a single token, and upon 
eating a newline CHKALIAS should be dropped. readtoken() has no way of 
distinguishing between these two cases with just a single CHKALIAS flag, 
so this will require a bit more complicated work to fix.

Cheers,
Harald van Dijk

Re: Another alias substitution bug, now involving case statements

[Harald van Dijk]

On 25/01/2020 17:29, Harald van Dijk wrote:
> Hi,
> 
> Checking alias substitution handling in more detail after Martijn 
> Dekker's report, I found another case where I believe dash's behaviour 
> is incorrect. First, please consider this test:
> 
>    alias a="case x in " b=x
>    a b) echo hi ;; esac
> 
> bash, ksh and pdksh never check whether a case pattern is a valid alias 
> name, so they print nothing.
> 
> bosh, dash, mksh, yash and zsh do allow the space at the end of a's 
> definition to cause b to be considered as an alias name.
> 
> Based on the literal text of the current standard, I believe 
> bash/ksh/pdksh's behaviour is correct. Based on accepted new wording for 
> the standard, new wording that was drafted without considering this 
> special case, I believe the bosh/dash/mksh/yash/zsh behaviour is 
> correct. I would not at this time consider this a bug in any of the shells.
> 
> Now, consider this modified version:
> 
>    alias a="case x in " b=x
>    a
>    b) echo hi ;; esac
> 
> Here, the next token after "a" is a newline token, not b. Here, b must 
> definitely not be considered as an alias name. bosh, dash, mksh and zsh 
> do perform alias substitution anyway, yash does not.
> 
> The problem here is in the "eat newlines" behaviour of readtoken(). 
> There are two reasons why CHKALIAS might be set. It might be set because 
> the parser is in a state where the next token could be the start of a 
> simple command, or it might be set because the parser processed a blank 
> at the end of a prior alias definition. In the first case, after eating 
> a newline, the parser is still in a state where the next token could be 
> the start of a simple command, so CHKALIAS should not be dropped. In the 
> second case, the blank should only affect a single token, and upon 
> eating a newline CHKALIAS should be dropped. readtoken() has no way of 
> distinguishing between these two cases with just a single CHKALIAS flag, 
> so this will require a bit more complicated work to fix.

Not very complicated after all. One flag in kwd and one flag in checkkwd 
will do the job. kwd tracks whether CHKALIAS was set prior to the call 
to readtoken(), i.e. whether this is potentially the start of a simple 
command. checkkwd tracks whether CHKALIAS was/got set at the last 
xxreadtoken() call.

--- a/src/parser.c
+++ b/src/parser.c
@@ -713,6 +713,7 @@ top:
         if (kwd & CHKNL) {
                 while (t == TNL) {
                         parseheredoc();
+                       checkkwd = 0;
                         t = xxreadtoken();
                 }
         }
@@ -734,7 +735,7 @@ top:
                 }
         }

-       if (checkkwd & CHKALIAS) {
+       if ((checkkwd | kwd) & CHKALIAS) {
                 struct alias *ap;
                 if ((ap = lookupalias(wordtext, 1)) != NULL) {
                         if (*ap->val) {

I have checked that this handles both my cases here and the test cases 
in Martijn Dekker's thread.

> Cheers,
> Harald van Dijk