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

3 files changed, 6 insertions, 6 deletions

diff --git a/src/interfaces/ecpg/test/expected/preproc-strings.c b/src/interfaces/ecpg/test/expected/preproc-strings.c
index e695007b133..1e50cd36c38 100644
--- a/src/interfaces/ecpg/test/expected/preproc-strings.c
+++ b/src/interfaces/ecpg/test/expected/preproc-strings.c
@@ -45,7 +45,7 @@ int main(void)
 #line 13 "strings.pgc"
 
 
-  { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select 'abcdef' , N'abcdef' as foo , E'abc\\bdef' as \"foo\" , U&'d\\0061t\\0061' as U&\"foo\" , U&'d!+000061t!+000061' UESCAPE '!' , $foo$abc$def$foo$", ECPGt_EOIT, 
+  { ECPGdo(__LINE__, 0, 1, NULL, 0, ECPGst_normal, "select 'abc''d\\ef' , N'abc''d\\ef' as foo , E'abc''d\\\\ef' as \"foo\"\"bar\" , U&'d\\0061t\\0061' as U&\"foo\"\"bar\" , U&'d!+000061t!+000061' UESCAPE '!' , $foo$abc$def$foo$", ECPGt_EOIT, 
 	ECPGt_char,&(s1),(long)0,(long)1,(1)*sizeof(char), 
 	ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, 
 	ECPGt_char,&(s2),(long)0,(long)1,(1)*sizeof(char), 
diff --git a/src/interfaces/ecpg/test/expected/preproc-strings.stderr b/src/interfaces/ecpg/test/expected/preproc-strings.stderr
index dbc9e5c0b8d..4c3a8eee5aa 100644
--- a/src/interfaces/ecpg/test/expected/preproc-strings.stderr
+++ b/src/interfaces/ecpg/test/expected/preproc-strings.stderr
@@ -8,7 +8,7 @@
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_process_output on line 13: OK: SET
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_execute on line 15: query: select 'abcdef' , N'abcdef' as foo , E'abc\bdef' as "foo" , U&'d\0061t\0061' as U&"foo" , U&'d!+000061t!+000061' UESCAPE '!' , $foo$abc$def$foo$; with 0 parameter(s) on connection ecpg1_regression
+[NO_PID]: ecpg_execute on line 15: query: select 'abc''d\ef' , N'abc''d\ef' as foo , E'abc''d\\ef' as "foo""bar" , U&'d\0061t\0061' as U&"foo""bar" , U&'d!+000061t!+000061' UESCAPE '!' , $foo$abc$def$foo$; with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_execute on line 15: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
@@ -16,15 +16,15 @@
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_store_result on line 15: allocating memory for 1 tuples
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 15: RESULT: abcdef offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 15: RESULT: abc'd\ef offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_store_result on line 15: allocating memory for 1 tuples
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 15: RESULT: abcdef offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 15: RESULT: abc'd\ef offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_store_result on line 15: allocating memory for 1 tuples
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_get_data on line 15: RESULT: abcdef offset: -1; array: no
+[NO_PID]: ecpg_get_data on line 15: RESULT: abc'd\ef offset: -1; array: no
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_store_result on line 15: allocating memory for 1 tuples
 [NO_PID]: sqlca: code: 0, state: 00000
diff --git a/src/interfaces/ecpg/test/expected/preproc-strings.stdout b/src/interfaces/ecpg/test/expected/preproc-strings.stdout
index 730d72dd64e..1456b152d78 100644
--- a/src/interfaces/ecpg/test/expected/preproc-strings.stdout
+++ b/src/interfaces/ecpg/test/expected/preproc-strings.stdout
@@ -1 +1 @@
-abcdef abcdef abcdef data data abc$def
+abc'd\ef abc'd\ef abc'd\ef data data abc$def