Make psql reject attempts to set special variables to invalid values.

Previously, if the user set a special variable such as ECHO to an
unrecognized value, psql would bleat but store the new value anyway, and
then fall back to a default setting for the behavior controlled by the
variable.  This was agreed to be a not particularly good idea.  With
this patch, invalid values result in an error message and no change in
state.

(But this applies only to variables that affect psql's behavior; purely
informational variables such as ENCODING can still be set to random
values.)

To do this, modify the API for psql's assign-hook functions so that they
can return an OK/not OK result, and give them the responsibility for
printing error messages when they reject a value.  Adjust the APIs for
ParseVariableBool and ParseVariableNum to support the new behavior
conveniently.

In passing, document the variable VERSION, which had somehow escaped that.
And improve the quite-inadequate commenting in psql/variables.c.

Daniel Vérité, reviewed by Rahila Syed, some further tweaking by me

Discussion: https://postgr.es/m/7356e741-fa59-4146-a8eb-cf95fd6b21fb@mm

2 files changed, 18 insertions, 1 deletions

diff --git a/src/test/regress/expected/psql.out b/src/test/regress/expected/psql.out
index 464436ab3b..420825aa56 100644
--- a/src/test/regress/expected/psql.out
+++ b/src/test/regress/expected/psql.out
@@ -2,6 +2,15 @@
 -- Tests for psql features that aren't closely connected to any
 -- specific server features
 --
+-- \set
+-- fail: invalid name
+\set invalid/name foo
+invalid variable name: "invalid/name"
+-- fail: invalid value for special variable
+\set AUTOCOMMIT foo
+unrecognized value "foo" for "AUTOCOMMIT": boolean expected
+\set FETCH_COUNT foo
+invalid value "foo" for "FETCH_COUNT": integer expected
 -- \gset
 select 10 as test01, 20 as test02, 'Hello' as test03 \gset pref01_
 \echo :pref01_test01 :pref01_test02 :pref01_test03
@@ -9,7 +18,7 @@ select 10 as test01, 20 as test02, 'Hello' as test03 \gset pref01_
 -- should fail: bad variable name
 select 10 as "bad name"
 \gset
-could not set variable "bad name"
+invalid variable name: "bad name"
 -- multiple backslash commands in one line
 select 1 as x, 2 as y \gset pref01_ \\ \echo :pref01_x
 1
diff --git a/src/test/regress/sql/psql.sql b/src/test/regress/sql/psql.sql
index 900aa7ee1e..79624b9193 100644
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -3,6 +3,14 @@
 -- specific server features
 --
 
+-- \set
+
+-- fail: invalid name
+\set invalid/name foo
+-- fail: invalid value for special variable
+\set AUTOCOMMIT foo
+\set FETCH_COUNT foo
+
 -- \gset
 
 select 10 as test01, 20 as test02, 'Hello' as test03 \gset pref01_