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Avoid premature de-doubling of quote marks in ECPG strings.

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If you write the literal 'abc''def' in an EXEC SQL command, that will
come out the other end as 'abc'def', triggering a syntax error in the
backend.  Likewise, "abc""def" is reduced to "abc"def" which is wrong
syntax for a quoted identifier.

The cause is that the lexer thinks it should emit just one quote
mark, whereas what it really should do is keep the string as-is.

Add some docs and test cases, too.

Although this seems clearly a bug, I fear users wouldn't appreciate
changing it in minor releases.  Some may well be working around it
by applying an extra doubling of affected quotes, as for example
sql/dyntest.pgc has been doing.

Per investigation of a report from 1250kv, although this isn't
exactly what he/she was on about.

Discussion: https://postgr.es/m/673825.1603223178@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2020-10-22 17:34:32 -04:00
parent 8bb0c9770e
commit 3dfb1942d9
7 changed files with 28 additions and 20 deletions
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17
doc/src/sgml/ecpg.sgml
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@ -31,7 +31,7 @@
specially marked sections. To build the program, the source code (<filename>*.pgc</filename>)
is first passed through the embedded SQL preprocessor, which converts it
to an ordinary C program (<filename>*.c</filename>), and afterwards it can be processed by a C
compiler. (For details about the compiling and linking see <xref linkend="ecpg-process"/>).
compiler. (For details about the compiling and linking see <xref linkend="ecpg-process"/>.)
Converted ECPG applications call functions in the libpq library
through the embedded SQL library (ecpglib), and communicate with
the PostgreSQL server using the normal frontend-backend protocol.
@ -63,11 +63,22 @@ EXEC SQL ...;
</programlisting>
These statements syntactically take the place of a C statement.
Depending on the particular statement, they can appear at the
global level or within a function. Embedded
global level or within a function.
</para>
<para>
Embedded
<acronym>SQL</acronym> statements follow the case-sensitivity rules of
normal <acronym>SQL</acronym> code, and not those of C. Also they allow nested
C-style comments that are part of the SQL standard. The C part of the
C-style comments as per the SQL standard. The C part of the
program, however, follows the C standard of not accepting nested comments.
Embedded <acronym>SQL</acronym> statements likewise use SQL rules, not
C rules, for parsing quoted strings and identifiers.
(See <xref linkend="sql-syntax-strings"/> and
<xref linkend="sql-syntax-identifiers"/> respectively. Note that
ECPG assumes that <varname>standard_conforming_strings</varname>
is <literal>on</literal>.)
Of course, the C part of the program follows C quoting rules.
</para>
<para>