Re-implement pl/pgsql's expression and assignment parsing.

Invent new RawParseModes that allow the core grammar to handle
pl/pgsql expressions and assignments directly, and thereby get rid
of a lot of hackery in pl/pgsql's parser.  This moves a good deal
of knowledge about pl/pgsql into the core code: notably, we have to
invent a CoercionContext that matches pl/pgsql's (rather dubious)
historical behavior for assignment coercions.  That's getting away
from the original idea of pl/pgsql as an arm's-length extension of
the core, but really we crossed that bridge a long time ago.

The main advantage of doing this is that we can now use the core
parser to generate FieldStore and/or SubscriptingRef nodes to handle
assignments to pl/pgsql variables that are records or arrays.  That
fixes a number of cases that had never been implemented in pl/pgsql
assignment, such as nested records and array slicing, and it allows
pl/pgsql assignment to support the datatype-specific subscripting
behaviors introduced in commit c7aba7c14.

There are cosmetic benefits too: when a syntax error occurs in a
pl/pgsql expression, the error report no longer includes the confusing
"SELECT" keyword that used to get prefixed to the expression text.
Also, there seem to be some small speed gains.

Discussion: https://postgr.es/m/4165684.1607707277@sss.pgh.pa.us

1 files changed, 46 insertions, 8 deletions

diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 6c0593686a..e28d242922 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -51,6 +51,12 @@ static _SPI_connection *_SPI_current = NULL;
 static int	_SPI_stack_depth = 0;	/* allocated size of _SPI_stack */
 static int	_SPI_connected = -1;	/* current stack index */
 
+typedef struct SPICallbackArg
+{
+	const char *query;
+	RawParseMode mode;
+} SPICallbackArg;
+
 static Portal SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
 									   ParamListInfo paramLI, bool read_only);
 
@@ -1479,6 +1485,7 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
 	Snapshot	snapshot;
 	MemoryContext oldcontext;
 	Portal		portal;
+	SPICallbackArg spicallbackarg;
 	ErrorContextCallback spierrcontext;
 
 	/*
@@ -1533,8 +1540,10 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
 	 * Setup error traceback support for ereport(), in case GetCachedPlan
 	 * throws an error.
 	 */
+	spicallbackarg.query = plansource->query_string;
+	spicallbackarg.mode = plan->parse_mode;
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = unconstify(char *, plansource->query_string);
+	spierrcontext.arg = &spicallbackarg;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -1952,6 +1961,7 @@ SPI_plan_get_cached_plan(SPIPlanPtr plan)
 {
 	CachedPlanSource *plansource;
 	CachedPlan *cplan;
+	SPICallbackArg spicallbackarg;
 	ErrorContextCallback spierrcontext;
 
 	Assert(plan->magic == _SPI_PLAN_MAGIC);
@@ -1966,8 +1976,10 @@ SPI_plan_get_cached_plan(SPIPlanPtr plan)
 	plansource = (CachedPlanSource *) linitial(plan->plancache_list);
 
 	/* Setup error traceback support for ereport() */
+	spicallbackarg.query = plansource->query_string;
+	spicallbackarg.mode = plan->parse_mode;
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = unconstify(char *, plansource->query_string);
+	spierrcontext.arg = &spicallbackarg;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -2094,13 +2106,16 @@ _SPI_prepare_plan(const char *src, SPIPlanPtr plan)
 	List	   *raw_parsetree_list;
 	List	   *plancache_list;
 	ListCell   *list_item;
+	SPICallbackArg spicallbackarg;
 	ErrorContextCallback spierrcontext;
 
 	/*
 	 * Setup error traceback support for ereport()
 	 */
+	spicallbackarg.query = src;
+	spicallbackarg.mode = plan->parse_mode;
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = unconstify(char *, src);
+	spierrcontext.arg = &spicallbackarg;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -2199,13 +2214,16 @@ _SPI_prepare_oneshot_plan(const char *src, SPIPlanPtr plan)
 	List	   *raw_parsetree_list;
 	List	   *plancache_list;
 	ListCell   *list_item;
+	SPICallbackArg spicallbackarg;
 	ErrorContextCallback spierrcontext;
 
 	/*
 	 * Setup error traceback support for ereport()
 	 */
+	spicallbackarg.query = src;
+	spicallbackarg.mode = plan->parse_mode;
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = unconstify(char *, src);
+	spierrcontext.arg = &spicallbackarg;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -2263,6 +2281,7 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 	SPITupleTable *my_tuptable = NULL;
 	int			res = 0;
 	bool		pushed_active_snap = false;
+	SPICallbackArg spicallbackarg;
 	ErrorContextCallback spierrcontext;
 	CachedPlan *cplan = NULL;
 	ListCell   *lc1;
@@ -2270,8 +2289,10 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 	/*
 	 * Setup error traceback support for ereport()
 	 */
+	spicallbackarg.query = NULL;	/* we'll fill this below */
+	spicallbackarg.mode = plan->parse_mode;
 	spierrcontext.callback = _SPI_error_callback;
-	spierrcontext.arg = NULL;	/* we'll fill this below */
+	spierrcontext.arg = &spicallbackarg;
 	spierrcontext.previous = error_context_stack;
 	error_context_stack = &spierrcontext;
 
@@ -2318,7 +2339,7 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 		List	   *stmt_list;
 		ListCell   *lc2;
 
-		spierrcontext.arg = unconstify(char *, plansource->query_string);
+		spicallbackarg.query = plansource->query_string;
 
 		/*
 		 * If this is a one-shot plan, we still need to do parse analysis.
@@ -2722,7 +2743,8 @@ _SPI_pquery(QueryDesc *queryDesc, bool fire_triggers, uint64 tcount)
 static void
 _SPI_error_callback(void *arg)
 {
-	const char *query = (const char *) arg;
+	SPICallbackArg *carg = (SPICallbackArg *) arg;
+	const char *query = carg->query;
 	int			syntaxerrposition;
 
 	if (query == NULL)			/* in case arg wasn't set yet */
@@ -2740,7 +2762,23 @@ _SPI_error_callback(void *arg)
 		internalerrquery(query);
 	}
 	else
-		errcontext("SQL statement \"%s\"", query);
+	{
+		/* Use the parse mode to decide how to describe the query */
+		switch (carg->mode)
+		{
+			case RAW_PARSE_PLPGSQL_EXPR:
+				errcontext("SQL expression \"%s\"", query);
+				break;
+			case RAW_PARSE_PLPGSQL_ASSIGN1:
+			case RAW_PARSE_PLPGSQL_ASSIGN2:
+			case RAW_PARSE_PLPGSQL_ASSIGN3:
+				errcontext("PL/pgSQL assignment \"%s\"", query);
+				break;
+			default:
+				errcontext("SQL statement \"%s\"", query);
+				break;
+		}
+	}
 }
 
 /*