psql: improve tab-complete's handling of variant SQL names.

This patch improves tab completion's ability to deal with
valid variant spellings of SQL identifiers.  Notably:

* Unquoted upper-case identifiers are now downcased as the backend
would do, allowing them to be completed correctly.

* Tab completion can now match identifiers that are quoted even
though they don't need to be; for example "f<TAB> now completes
to "foo" if that's the only available name.  Previously, only
names that require quotes would be offered.

* Schema-qualified identifiers are now supported where SQL syntax
allows it; many lesser-used completion rules neglected this.

* Completion operations that refer back to some previously-typed
name (for example, to complete names of columns belonging to a
previously-mentioned table) now allow variant spellings of the
previous name too.

In addition, performance of tab completion queries has been
improved for databases containing many objects, although
you'd only be likely to notice with a heavily-loaded server.

Authors of future tab-completion patches should note that this
commit changes many details about how tab completion queries
must be written:

* Tab completion queries now deal in raw object names; do not
use quote_ident().

* The name-matching restriction in a query must now be written
as "outputcol LIKE '%s'", not "substring(outputcol,1,%d)='%s'".

* The SchemaQuery mechanism has been extended so that it can
handle queries that refer back to a previous name.  Most completion
queries that do that should be converted to SchemaQuery form.
Only consider using a literal query if the previous name can
never be schema-qualified.  Don't use a literal query if the
name-to-be-completed can validly be schema-qualified, either.

* Use set_completion_reference() to specify which word is the previous
name to consider, for either a SchemaQuery or a literal query.

* If you want to offer some keywords in addition to a query result
(for example, offer COLUMN in addition to column names after
"ALTER TABLE t RENAME"), do not use the old hack of tacking the
keywords on with UNION.  Instead use the new QUERY_PLUS macros
to write such keywords separately from the query proper.  The
"addon" macro arguments that used to be used for this purpose
are gone.

* If your query returns something that's not a SQL identifier
(such as an attribute number or enum label), use the new
QUERY_VERBATIM macros to prevent the result from incorrectly
getting double-quoted.  You may still need to use quote_literal
in such a query, too.

Tom Lane and Haiying Tang

Discussion: https://postgr.es/m/a63cbd45e3884cf9b3961c2a6a95dcb7@G08CNEXMBPEKD05.g08.fujitsu.local

src/bin/psql/t/010_tab_completion.pl

@@ -40,10 +40,11 @@ $node->start;
 
 # set up a few database objects
 $node->safe_psql('postgres',
-	    "CREATE TABLE tab1 (f1 int, f2 text);\n"
+	    "CREATE TABLE tab1 (f1 int primary key, f2 text);\n"
 	  . "CREATE TABLE mytab123 (f1 int, f2 text);\n"
 	  . "CREATE TABLE mytab246 (f1 int, f2 text);\n"
-	  . "CREATE TYPE enum1 AS ENUM ('foo', 'bar', 'baz');\n");
+	  . "CREATE TABLE \"mixedName\" (f1 int, f2 text);\n"
+	  . "CREATE TYPE enum1 AS ENUM ('foo', 'bar', 'baz', 'BLACK');\n");
 
 # Developers would not appreciate this test adding a bunch of junk to
 # their ~/.psql_history, so be sure to redirect history into a temp file.
@@ -176,6 +177,38 @@ check_completion("2\t", qr/246 /,
 
 clear_query();
 
+# check handling of quoted names
+check_completion(
+	"select * from \"my\t",
+	qr/select \* from "my\a?tab/,
+	"complete \"my<tab> to \"mytab when there are multiple choices");
+
+check_completion(
+	"\t\t",
+	qr/"mytab123" +"mytab246"/,
+	"offer multiple quoted table choices");
+
+check_completion("2\t", qr/246" /,
+	"finish completion of one of multiple quoted table choices");
+
+clear_query();
+
+# check handling of mixed-case names
+check_completion(
+	"select * from \"mi\t",
+	qr/"mixedName"/,
+	"complete a mixed-case name");
+
+clear_query();
+
+# check case folding
+check_completion(
+	"select * from TAB\t",
+	qr/tab1 /,
+	"automatically fold case");
+
+clear_query();
+
 # check case-sensitive keyword replacement
 # note: various versions of readline/libedit handle backspacing
 # differently, so just check that the replacement comes out correctly
@@ -183,6 +216,48 @@ check_completion("\\DRD\t", qr/drds /, "complete \\DRD<tab> to \\drds");
 
 clear_query();
 
+# check completion of a schema-qualified name
+check_completion(
+	"select * from pub\t",
+	qr/public\./,
+	"complete schema when relevant");
+
+check_completion(
+	"tab\t",
+	qr/tab1 /,
+	"complete schema-qualified name");
+
+clear_query();
+
+check_completion(
+	"select * from PUBLIC.t\t",
+	qr/public\.tab1 /,
+	"automatically fold case in schema-qualified name");
+
+clear_query();
+
+# check interpretation of referenced names
+check_completion(
+	"alter table tab1 drop constraint \t",
+	qr/tab1_pkey /,
+	"complete index name for referenced table");
+
+clear_query();
+
+check_completion(
+	"alter table TAB1 drop constraint \t",
+	qr/tab1_pkey /,
+	"complete index name for referenced table, with downcasing");
+
+clear_query();
+
+check_completion(
+	"alter table public.\"tab1\" drop constraint \t",
+	qr/tab1_pkey /,
+	"complete index name for referenced table, with schema and quoting");
+
+clear_query();
+
 # check filename completion
 check_completion(
 	"\\lo_import tmp_check/some\t",
@@ -234,6 +309,23 @@ check_completion(
 
 clear_line();
 
+# enum labels are case sensitive, so this should complete BLACK immediately
+check_completion(
+	"ALTER TYPE enum1 RENAME VALUE 'B\t",
+	qr|BLACK|,
+	"enum labels are case sensitive");
+
+clear_line();
+
+# check completion of a keyword offered in addition to object names
+# (that code path currently doesn't preserve case of what's typed)
+check_completion(
+	"comment on constraint foo on dom\t",
+	qr|DOMAIN|,
+	"offer keyword in addition to query result");
+
+clear_query();
+
 # send psql an explicit \q to shut it down, else pty won't close properly
 $timer->start(5);
 $in .= "\\q\n";