gen/c: fix double evaluation of rvalue array expression in slice

vlib/v/gen/c/index.v

@@ -62,6 +62,7 @@ fn (mut g Gen) range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 	mut tmp_opt := ''
 	mut cur_line := ''
 	mut gen_or := node.or_expr.kind != .absent || node.is_option
+	mut tmp_left := ''
 
 	if sym.kind == .string {
 		if node.is_gated {
@@ -82,6 +83,15 @@ fn (mut g Gen) range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 		}
 		g.expr(node.left)
 	} else if sym.kind == .array {
+		if !range.has_high {
+			tmp_left = g.new_tmp_var()
+			line := g.go_before_stmt(0)
+			g.out.write_string(util.tabs(g.indent))
+			tmp_type := g.typ(node.left_type)
+			g.write('$tmp_type $tmp_left = ')
+			g.expr(node.left)
+			g.write(';\n$line')
+		}
 		if node.is_gated {
 			g.write('array_slice_ni(')
 		} else {
@@ -90,7 +100,11 @@ fn (mut g Gen) range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 		if node.left_type.is_ptr() {
 			g.write('*')
 		}
-		g.expr(node.left)
+		if range.has_high {
+			g.expr(node.left)
+		} else {
+			g.write(tmp_left)
+		}
 	} else if sym.kind == .array_fixed {
 		// Convert a fixed array to V array when doing `fixed_arr[start..end]`
 		info := sym.info as ast.ArrayFixed
@@ -132,15 +146,16 @@ fn (mut g Gen) range_expr(node ast.IndexExpr, range ast.RangeExpr) {
 	} else if sym.kind == .array_fixed {
 		info := sym.info as ast.ArrayFixed
 		g.write('$info.size')
-	} else if node.left_type.is_ptr() {
-		g.write('(')
-		g.write('*')
-		g.expr(node.left)
-		g.write(')')
-		g.write('.len')
+	} else if sym.kind == .array {
+		if node.left_type.is_ptr() {
+			g.write('${tmp_left}->len')
+		} else {
+			g.write('${tmp_left}.len')
+		}
 	} else {
+		g.write('(')
 		g.expr(node.left)
-		g.write('.len')
+		g.write(').len')
 	}
 	g.write(')')
 

vlib/v/tests/slice_rval_test.v

@@ -0,0 +1,8 @@
+fn test_arr_rval() {
+	a := [1,2]
+	s := (*&a)[..]
+	assert s == a
+	
+	b := unsafe {*&[]int(&a)}[..]
+	assert b == a
+}