patch 9.0.2057: Vim9: no strict type checks for funcrefs varargsv9.0.2057

Problem:  Vim9: no strict type checks for funcrefs varargs
Solution: Perform strict type checking when declaring funcrefs
          with vararg declaration, add tests

closes: #13397

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ernie Rael <errael@raelity.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/runtime/doc/vim9.txt b/runtime/doc/vim9.txt
index 6cabb870d8..58d9ed6142 100644
--- a/runtime/doc/vim9.txt
+++ b/runtime/doc/vim9.txt
@@ -1468,7 +1468,7 @@ return value) results in error *E1031*  *E1186* .
 There is no array type, use list<{type}> instead.  For a list constant an
 efficient implementation is used that avoids allocating a lot of small pieces
 of memory.
-							*E1005* *E1007*
+				    *vim9-func-declaration* *E1005* *E1007*
 A partial and function can be declared in more or less specific ways:
 func				any kind of function reference, no type
 				checking for arguments or return value
@@ -1669,6 +1669,26 @@ Same for |extend()|, use |extendnew()| instead, and for |flatten()|, use
 |flattennew()| instead.  Since |flatten()| is intended to always change the
 type, it can not be used in Vim9 script.
 
+Assigning to a funcref with specified arguments (see |vim9-func-declaration|)
+does strict type checking of the arguments. For variable number of arguments
+the type must match: >
+	var FuncRef: func(string, number, bool): number
+	FuncRef = (v1: string, v2: number, v3: bool) => 777	# OK
+	FuncRef = (v1: string, v2: number, v3: number) => 777	# Error!
+	# variable number of arguments must have same type
+	var FuncVA: func(...list<string>): number
+	FuncVA = (...v: list<number>): number => v  # Error!
+	FuncVA = (...v: list<any>): number => v	    # OK, `any` runtime check
+	FuncVA = (v1: string, v: string2): number => 333     # Error!
+	FuncVA = (v: list<string>): number => 3	    # Error!
+
+If the destinataion funcref has no specified arguments, then there is no
+argument type checking: >
+	var FuncUnknownArgs: func: number
+	FuncUnknownArgs = (v): number => v			# OK
+	FuncUnknownArgs = (v1: string, v2: string): number => 3	# OK
+<	FuncUnknownArgs = (...v1: list<string>): number => 333	# OK
+
 			 *E1211* *E1217* *E1218* *E1219* *E1220* *E1221*
 			 *E1222* *E1223* *E1224* *E1225* *E1226* *E1227*
 			 *E1228* *E1238* *E1250* *E1251* *E1252* *E1256*