Don't require a loaded function to have "compile lints" applied. (#327)

Loading an existing, compiled function should not require that it was
previously compiled with the set of lints PL/Rust now uses for
compilation.  This prohibits newer versions of PL/Rust, which might have
a new lint, from executing functions created with an older version
without that lint.

We do, however, continue to require the lints that are set in both the
`$PLRUST_REQUIRED_LINTS` envar and the `plrust.required_lints`
postgresql.conf GUC.

This is a way for the administrator to flat out **require** that certain
lints be applied to **every** function before it can be loaded/executed.

PL/Rust's default stance, however, is that if it was good before, it's
good now, even if new lints are applied going forward.

Author: eeeebbbbrrrr

plrust/src/gucs.rs

@@ -27,8 +27,7 @@ pub(crate) static PLRUST_ALLOWED_DEPENDENCIES: GucSetting<Option<&'static str>>
 static PLRUST_COMPILATION_TARGETS: GucSetting<Option<&'static str>> = GucSetting::new(None);
 pub(crate) static PLRUST_COMPILE_LINTS: GucSetting<Option<&'static str>> =
     GucSetting::new(Some(DEFAULT_LINTS));
-pub(crate) static PLRUST_REQUIRED_LINTS: GucSetting<Option<&'static str>> =
-    GucSetting::new(Some(DEFAULT_LINTS));
+pub(crate) static PLRUST_REQUIRED_LINTS: GucSetting<Option<&'static str>> = GucSetting::new(None);
 pub(crate) static PLRUST_TRUSTED_PGRX_VERSION: GucSetting<Option<&'static str>> =
     GucSetting::new(Some(env!(
         "PLRUST_TRUSTED_PGRX_VERSION",

plrust/src/user_crate/lint.rs

@@ -127,7 +127,7 @@ pub(crate) fn required_lints() -> LintSet {
     // whatever might be configured in postgresql.conf
     let mut configured = PLRUST_REQUIRED_LINTS
         .get()
-        .unwrap_or_else(|| PLRUST_COMPILE_LINTS.get().unwrap_or_default())
+        .unwrap_or_default()
         .split(',')
         .filter_map(filter_map)
         .collect::<LintSet>();