[perl #80368] Fix implicit assignop in qq"a\U="

The bug report explains it all:
> $ perl -e 'print "a\U="'
> Can't modify constant item in concatenation (.) or string at -e line 1, near "print "a\U=""
> Execution of -e aborted due to compilation errors.
>
> The "a\U=" string constant ought to generate ops corresponding roughly to
> "a".uc("=") (which would then be constant-folded).  However, the "=" is
> being interpreted by the tokeniser as part of the concatenation operator,
> producing ops corresponding to "a".=uc("") (which generates the error).
>
> This happens because the implicit concatenation operator is generated
> in toke.c via the Aop() macro, which allows an addition-type operator
> to be mutated into an assignment operator if it is immediately followed
> by an "=".  It should instead be generated via one of the other macros,
> or possibly a new macro, that doesn't allow for mutation to an assignment
> operator.

This commit does the latter.

> There are multiple sites in toke.c making the same mistake.

The other two instances are harmless, but the next commit will change
them for a different reason (avoiding unnecessary PL_expect assign-
ments with a view to eventually removing PL_lex_expect).

1 files changed, 3 insertions, 1 deletions

diff --git a/toke.c b/toke.c
index 68cf152d48..a7ba403108 100644
--- a/toke.c
+++ b/toke.c
@@ -196,6 +196,7 @@ static const char* const lex_state_names[] = {
  * PWop         : power operator
  * PMop         : pattern-matching operator
  * Aop          : addition-level operator
+ * AopNOASSIGN  : addition-level operator that is never part of .=
  * Mop          : multiplication-level operator
  * Eop          : equality-testing operator
  * Rop          : relational operator <= != gt
@@ -232,6 +233,7 @@ static const char* const lex_state_names[] = {
 #define PWop(f)  return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)POWOP)))
 #define PMop(f)  return(pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)MATCHOP))
 #define Aop(f)   return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)ADDOP)))
+#define AopNOASSIGN(f) return (pl_yylval.ival=f, PL_bufptr=s, REPORT((int)ADDOP))
 #define Mop(f)   return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)MULOP)))
 #define Eop(f)   return (pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)EQOP))
 #define Rop(f)   return (pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)RELOP))
@@ -4390,7 +4392,7 @@ Perl_yylex(pTHX)
 		if (PL_lex_casemods == 1 && PL_lex_inpat)
 		    OPERATOR(',');
 		else
-		    Aop(OP_CONCAT);
+		    AopNOASSIGN(OP_CONCAT);
 	    }
 	    else
 		return yylex();