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

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

1 files changed, 14 insertions, 3 deletions

diff --git a/doc/src/sgml/ecpg.sgml b/doc/src/sgml/ecpg.sgml
index 6e3ca788f6e..419574e9ea6 100644
--- a/doc/src/sgml/ecpg.sgml
+++ b/doc/src/sgml/ecpg.sgml
@@ -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>