parser: support `x = a[k] ?` propagation for arrays and maps (#8199)

vlib/v/parser/parser.v

@@ -1394,33 +1394,45 @@ fn (mut p Parser) index_expr(left ast.Expr) ast.IndexExpr {
 	// [expr]
 	pos := start_pos.extend(p.tok.position())
 	p.check(.rsbr)
-	// a[i] or { ... }
-	if p.tok.kind == .key_orelse && !p.or_is_handled {
-		was_inside_or_expr := p.inside_or_expr
-		mut or_pos := p.tok.position()
-		p.next()
-		p.open_scope()
-		or_stmts := p.parse_block_no_scope(false)
-		or_pos = or_pos.extend(p.prev_tok.position())
-		p.close_scope()
-		p.inside_or_expr = was_inside_or_expr
-		return ast.IndexExpr{
-			left: left
-			index: expr
-			pos: pos
-			or_expr: ast.OrExpr{
-				kind: .block
-				stmts: or_stmts
-				pos: or_pos
+	mut or_kind := ast.OrKind.absent
+	mut or_stmts := []ast.Stmt{}
+	mut or_pos := token.Position{}
+	if !p.or_is_handled {
+		// a[i] or { ... }
+		if p.tok.kind == .key_orelse {
+			was_inside_or_expr := p.inside_or_expr
+			or_pos = p.tok.position()
+			p.next()
+			p.open_scope()
+			or_stmts = p.parse_block_no_scope(false)
+			or_pos = or_pos.extend(p.prev_tok.position())
+			p.close_scope()
+			p.inside_or_expr = was_inside_or_expr
+			return ast.IndexExpr{
+				left: left
+				index: expr
+				pos: pos
+				or_expr: ast.OrExpr{
+					kind: .block
+					stmts: or_stmts
+					pos: or_pos
+				}
 			}
 		}
+		// `a[i] ?`
+		if p.tok.kind == .question {
+			p.next()
+			or_kind = .propagate
+		}
 	}
 	return ast.IndexExpr{
 		left: left
 		index: expr
 		pos: pos
 		or_expr: ast.OrExpr{
-			kind: .absent
+			kind: or_kind
+			stmts: or_stmts
+			pos: or_pos
 		}
 	}
 }

vlib/v/parser/tests/or_default_missing.out

@@ -0,0 +1,14 @@
+vlib/v/parser/tests/or_default_missing.vv:4:3: error: `or` block must provide a default value of type `int`, or return/exit/continue/break/panic
+    2 |     m := [3, 4, 5]
+    3 |     el := m[4] or {
+    4 |         println('error')
+      |         ~~~~~~~~~~~~~~~~
+    5 |     }
+    6 |     println(el)
+vlib/v/parser/tests/or_default_missing.vv:16:16: error: last statement in the `or {}` block should be an expression of type `int` or exit parent scope
+   14 |     }
+   15 |     mut testvar := 0
+   16 |     el := m['pp'] or {
+      |                   ~~~~
+   17 |         testvar = 12
+   18 |     }

vlib/v/parser/tests/or_default_missing.vv

@@ -0,0 +1,20 @@
+fn test_array_or() {
+	m := [3, 4, 5]
+	el := m[4] or {
+		println('error')
+	}
+	println(el)
+}
+
+fn test_map_or() {
+	m := {
+		'as': 3
+		'qw': 4
+		'kl': 5
+	}
+	mut testvar := 0
+	el := m['pp'] or {
+		testvar = 12
+	}
+	println('$el $testvar')
+}

vlib/v/tests/array_map_or_test.v

@@ -33,3 +33,57 @@ fn test_map_or() {
 	assert el == 7
 	assert good == 5
 }
+
+
+fn get_map_el(key string) ?int {
+	m := {'as': 3, 'qw': 4, 'kl': 5}
+	r := m[key] ?
+	return r
+}
+
+fn get_arr_el(i int) ?int {
+	m := [3, 4, 5]
+	r := m[i] ?
+	return r
+}
+
+fn test_propagation() {
+	mut testvar1 := 12
+	mut testvar2 := 78
+	e := get_map_el('vv') or {
+		testvar1 = -34
+		7
+	}
+	f := get_map_el('as') or {
+		testvar1 = 67
+		23
+	}
+	g := get_arr_el(3) or {
+		testvar2 = 99
+		12
+	}
+	h := get_arr_el(0) or {
+		testvar2 = 177
+		int(-67)
+	}
+	assert testvar1 == -34
+	assert testvar2 == 99
+	assert e == 7
+	assert f == 3
+	assert g == 12
+	assert h == 3
+}
+
+fn get_arr_el_nested(i int) ?int {
+	ind := [2, 1, 0, 5]
+	m := [3, 4, 5]
+	r := m[ind[i]] ?
+	return r
+}
+
+fn test_nested_array_propagation() {
+	g := get_arr_el_nested(3) or {
+		12
+	}
+	assert g == 12
+}