Support \if ... \elif ... \else ... \endif in psql scripting.

This patch adds nestable conditional blocks to psql.  The control
structure feature per se is complete, but the boolean expressions
understood by \if and \elif are pretty primitive; basically, after
variable substitution and backtick expansion, the result has to be
"true" or "false" or one of the other standard spellings of a boolean
value.  But that's enough for many purposes, since you can always
do the heavy lifting on the server side; and we can extend it later.

Along the way, pay down some of the technical debt that had built up
around psql/command.c:
* Refactor exec_command() into a function per command, instead of
being a 1500-line monstrosity.  This makes the file noticeably longer
because of repetitive function header/trailer overhead, but it seems
much more readable.
* Teach psql_get_variable() and psqlscanslash.l to suppress variable
substitution and backtick expansion on the basis of the conditional
stack state, thereby allowing removal of the OT_NO_EVAL kluge.
* Fix the no-doubt-once-expedient hack of sometimes silently substituting
mainloop.c's previous_buf for query_buf when calling HandleSlashCmds.
(It's a bit remarkable that commands like \r worked at all with that.)
Recall of a previous query is now done explicitly in the slash commands
where that should happen.

Corey Huinker, reviewed by Fabien Coelho, further hacking by me

Discussion: https://postgr.es/m/CADkLM=c94OSRTnat=LX0ivNq4pxDNeoomFfYvBKM5N_xfmLtAA@mail.gmail.com

1 files changed, 144 insertions, 0 deletions

diff --git a/src/test/regress/sql/psql.sql b/src/test/regress/sql/psql.sql
index 8f8e17a87cd..0ae4dd84eab 100644
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -382,6 +382,150 @@ deallocate q;
 \pset expanded off
 \pset border 1
 
+-- tests for \if ... \endif
+
+\if true
+  select 'okay';
+  select 'still okay';
+\else
+  not okay;
+  still not okay
+\endif
+
+-- at this point query buffer should still have last valid line
+\g
+
+-- \if should work okay on part of a query
+select
+  \if true
+    42
+  \else
+    (bogus
+  \endif
+  forty_two;
+
+select \if false \\ (bogus \else \\ 42 \endif \\ forty_two;
+
+-- test a large nested if using a variety of true-equivalents
+\if true
+	\if 1
+		\if yes
+			\if on
+				\echo 'all true'
+			\else
+				\echo 'should not print #1-1'
+			\endif
+		\else
+			\echo 'should not print #1-2'
+		\endif
+	\else
+		\echo 'should not print #1-3'
+	\endif
+\else
+	\echo 'should not print #1-4'
+\endif
+
+-- test a variety of false-equivalents in an if/elif/else structure
+\if false
+	\echo 'should not print #2-1'
+\elif 0
+	\echo 'should not print #2-2'
+\elif no
+	\echo 'should not print #2-3'
+\elif off
+	\echo 'should not print #2-4'
+\else
+	\echo 'all false'
+\endif
+
+-- test simple true-then-else
+\if true
+	\echo 'first thing true'
+\else
+	\echo 'should not print #3-1'
+\endif
+
+-- test simple false-true-else
+\if false
+	\echo 'should not print #4-1'
+\elif true
+	\echo 'second thing true'
+\else
+	\echo 'should not print #5-1'
+\endif
+
+-- invalid boolean expressions are false
+\if invalid boolean expression
+	\echo 'will not print #6-1'
+\else
+	\echo 'will print anyway #6-2'
+\endif
+
+-- test un-matched endif
+\endif
+
+-- test un-matched else
+\else
+
+-- test un-matched elif
+\elif
+
+-- test double-else error
+\if true
+\else
+\else
+\endif
+
+-- test elif out-of-order
+\if false
+\else
+\elif
+\endif
+
+-- test if-endif matching in a false branch
+\if false
+    \if false
+        \echo 'should not print #7-1'
+    \else
+        \echo 'should not print #7-2'
+    \endif
+    \echo 'should not print #7-3'
+\else
+    \echo 'should print #7-4'
+\endif
+
+-- show that vars and backticks are not expanded when ignoring extra args
+\set foo bar
+\echo :foo :'foo' :"foo"
+\pset fieldsep | `nosuchcommand` :foo :'foo' :"foo"
+
+-- show that vars and backticks are not expanded and commands are ignored
+-- when in a false if-branch
+\set try_to_quit '\\q'
+\if false
+	:try_to_quit
+	\echo `nosuchcommand` :foo :'foo' :"foo"
+	\pset fieldsep | `nosuchcommand` :foo :'foo' :"foo"
+	\a \C arg1 \c arg1 arg2 arg3 arg4 \cd arg1 \conninfo
+	\copy arg1 arg2 arg3 arg4 arg5 arg6
+	\copyright \dt arg1 \e arg1 arg2
+	\ef whole_line
+	\ev whole_line
+	\echo arg1 arg2 arg3 arg4 arg5 \echo arg1 \encoding arg1 \errverbose
+	\g arg1 \gx arg1 \gexec \h \html \i arg1 \ir arg1 \l arg1 \lo arg1 arg2
+	\o arg1 \p \password arg1 \prompt arg1 arg2 \pset arg1 arg2 \q
+	\reset \s arg1 \set arg1 arg2 arg3 arg4 arg5 arg6 arg7 \setenv arg1 arg2
+	\sf whole_line
+	\sv whole_line
+	\t arg1 \T arg1 \timing arg1 \unset arg1 \w arg1 \watch arg1 \x arg1
+	-- \else here is eaten as part of OT_FILEPIPE argument
+	\w |/no/such/file \else
+	-- \endif here is eaten as part of whole-line argument
+	\! whole_line \endif
+\else
+	\echo 'should print #8-1'
+\endif
+
 -- SHOW_CONTEXT
 
 \set SHOW_CONTEXT never