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Add @extschema:name@ and no_relocate options to extensions.

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@extschema:name@ extends the existing @extschema@ feature so that
we can also insert the schema name of some required extension,
thus making cross-extension references robust even if they are in
different schemas.

However, this has the same hazard as @extschema@: if the schema
name is embedded literally in an installed object, rather than being
looked up once during extension script execution, then it's no longer
safe to relocate the other extension to another schema.  To deal with
that without restricting things unnecessarily, add a "no_relocate"
option to extension control files.  This allows an extension to
specify that it cannot handle relocation of some of its required
extensions, even if in themselves those extensions are relocatable.
We detect "no_relocate" requests of dependent extensions during
ALTER EXTENSION SET SCHEMA.

Regina Obe, reviewed by Sandro Santilli and myself

Discussion: https://postgr.es/m/003001d8f4ae$402282c0$c0678840$@pcorp.us
This commit is contained in:
Tom Lane
2023-03-20 18:37:11 -04:00
parent 30e9f2608a
commit 72a5b1fc88
12 changed files with 272 additions and 8 deletions
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45
doc/src/sgml/extend.sgml
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@ -739,6 +739,21 @@ RETURNS anycompatible AS ...
</listitem>
</varlistentry>
<varlistentry id="extend-extensions-files-no-relocate">
<term><varname>no_relocate</varname> (<type>string</type>)</term>
<listitem>
<para>
A list of names of extensions that this extension depends on that
should be barred from changing their schemas via <command>ALTER
EXTENSION ... SET SCHEMA</command>.
This is needed if this extension's script references the name
of a required extension's schema (using
the <literal>@extschema:<replaceable>name</replaceable>@</literal>
syntax) in a way that cannot track renames.
</para>
</listitem>
</varlistentry>
<varlistentry id="extend-extensions-files-superuser">
<term><varname>superuser</varname> (<type>boolean</type>)</term>
<listitem>
@ -902,8 +917,9 @@ RETURNS anycompatible AS ...
For such an extension, set <literal>relocatable = false</literal> in its
control file, and use <literal>@extschema@</literal> to refer to the target
schema in the script file. All occurrences of this string will be
replaced by the actual target schema's name before the script is
executed. The user can set the target schema using the
replaced by the actual target schema's name (double-quoted if
necessary) before the script is executed. The user can set the
target schema using the
<literal>SCHEMA</literal> option of <command>CREATE EXTENSION</command>.
</para>
</listitem>
@ -916,7 +932,7 @@ RETURNS anycompatible AS ...
will prevent use of the <literal>SCHEMA</literal> option of <command>CREATE
EXTENSION</command>, unless it specifies the same schema named in the control
file. This choice is typically necessary if the extension contains
internal assumptions about schema names that can't be replaced by
internal assumptions about its schema name that can't be replaced by
uses of <literal>@extschema@</literal>. The <literal>@extschema@</literal>
substitution mechanism is available in this case too, although it is
of limited use since the schema name is determined by the control file.
@ -969,6 +985,29 @@ SET LOCAL search_path TO @extschema@, pg_temp;
setting of <varname>search_path</varname> during creation of dependent
extensions.
</para>
<para>
If an extension references objects belonging to another extension,
it is recommended to schema-qualify those references. To do that,
write <literal>@extschema:<replaceable>name</replaceable>@</literal>
in the extension's script file, where <replaceable>name</replaceable>
is the name of the other extension (which must be listed in this
extension's <literal>requires</literal> list). This string will be
replaced by the name (double-quoted if necessary) of that extension's
target schema.
Although this notation avoids the need to make hard-wired assumptions
about schema names in the extension's script file, its use may embed
the other extension's schema name into the installed objects of this
extension. (Typically, that happens
when <literal>@extschema:<replaceable>name</replaceable>@</literal> is
used inside a string literal, such as a function body or
a <varname>search_path</varname> setting. In other cases, the object
reference is reduced to an OID during parsing and does not require
subsequent lookups.) If the other extension's schema name is so
embedded, you should prevent the other extension from being relocated
after yours is installed, by adding the name of the other extension to
this one's <literal>no_relocate</literal> list.
</para>
</sect2>
<sect2 id="extend-extensions-config-tables">