From 00563a130dfcac911e0ffbe871ea2b9ff9239172 Mon Sep 17 00:00:00 2001
From: Nick Treleaven <ntrel002@gmail.com>
Date: Fri, 18 Mar 2022 09:43:15 +0000
Subject: [PATCH] cgen: fix double evaluation of rvalue array expression in
 slice (#13737)

---
 vlib/v/gen/c/cgen.v            |  5 +++--
 vlib/v/gen/c/index.v           | 32 ++++++++++++++++++++++++--------
 vlib/v/tests/slice_rval_test.v |  8 ++++++++
 3 files changed, 35 insertions(+), 10 deletions(-)
 create mode 100644 vlib/v/tests/slice_rval_test.v

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index d576ede838..0c6b879a10 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -4795,7 +4795,7 @@ fn (mut g Gen) go_before_ternary() string {
 }
 
 fn (mut g Gen) insert_before_stmt(s string) {
-	cur_line := g.go_before_stmt(0)
+	cur_line := g.go_before_stmt(g.inside_ternary)
 	g.writeln(s)
 	g.write(cur_line)
 }
@@ -5643,7 +5643,8 @@ static inline __shared__$interface_name ${shared_fn_name}(__shared__$cctype* x)
 						if fargs.len > 1 {
 							methods_wrapper.write_string(', ')
 						}
-						methods_wrapper.writeln('${fargs[1..].join(', ')});')
+						args := fargs[1..].join(', ')
+						methods_wrapper.writeln('$args);')
 					} else {
 						if parameter_name.starts_with('__shared__') {
 							methods_wrapper.writeln('${method_call}(${fargs.join(', ')}->val);')
diff --git a/vlib/v/gen/c/index.v b/vlib/v/gen/c/index.v
index 08a041d9d5..8ff1dd7633 100644
--- a/vlib/v/gen/c/index.v
+++ b/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()
+			tmp_type := g.typ(node.left_type)
+			g.insert_before_stmt('${util.tabs(g.indent)}$tmp_type $tmp_left;')
+			// (tmp = expr, array_slice(...))
+			g.write('($tmp_left = ')
+			g.expr(node.left)
+			g.write(', ')
+		}
 		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 +146,17 @@ 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->')
+		} else {
+			g.write('${tmp_left}.')
+		}
+		g.write('len)')
 	} else {
+		g.write('(')
 		g.expr(node.left)
-		g.write('.len')
+		g.write(').len')
 	}
 	g.write(')')
 
diff --git a/vlib/v/tests/slice_rval_test.v b/vlib/v/tests/slice_rval_test.v
new file mode 100644
index 0000000000..2078f5b353
--- /dev/null
+++ b/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
+}