From 57cc00df222d3a8921f37c180a93d485b4bf2976 Mon Sep 17 00:00:00 2001
From: shove <shove@163.com>
Date: Thu, 28 Dec 2023 18:47:45 +0800
Subject: [PATCH] cgen: fix generating callexpr to string is actually called
 twice (fix #20282) (#20288)

---
 vlib/v/gen/c/str.v                            | 30 +++++++++++++++++--
 ...xpr_to_string_with_call_and_return_ref.out |  4 +++
 ...expr_to_string_with_call_and_return_ref.vv | 18 +++++++++++
 3 files changed, 49 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.out
 create mode 100644 vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.vv

diff --git a/vlib/v/gen/c/str.v b/vlib/v/gen/c/str.v
index a8a2f92a6..82376de02 100644
--- a/vlib/v/gen/c/str.v
+++ b/vlib/v/gen/c/str.v
@@ -111,12 +111,28 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 		is_dump_expr := expr is ast.DumpExpr
 		is_var_mut := expr.is_auto_deref_var()
 		str_fn_name := g.get_str_fn(exp_typ)
+		temp_var_needed := expr is ast.CallExpr && expr.return_type.is_ptr()
+		mut tmp_var := ''
+		if temp_var_needed {
+			tmp_var = g.new_tmp_var()
+			ret_typ := g.typ(exp_typ)
+			line := g.go_before_last_stmt().trim_space()
+			g.empty_line = true
+			g.write('${ret_typ} ${tmp_var} = ')
+			g.expr(expr)
+			g.writeln(';')
+			g.write(line)
+		}
 		if is_ptr && !is_var_mut {
 			ref_str := '&'.repeat(typ.nr_muls())
 			g.write('str_intp(1, _MOV((StrIntpData[]){{_SLIT("${ref_str}"), ${si_s_code} ,{.d_s = isnil(')
 			if typ.has_flag(.option) {
 				g.write('*(${g.base_type(exp_typ)}*)&')
-				g.expr(expr)
+				if temp_var_needed {
+					g.write(tmp_var)
+				} else {
+					g.expr(expr)
+				}
 				g.write('.data')
 				g.write(') ? _SLIT("Option(&nil)") : ')
 			} else {
@@ -125,7 +141,11 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 				defer {
 					g.inside_interface_deref = inside_interface_deref_old
 				}
-				g.expr(expr)
+				if temp_var_needed {
+					g.write(tmp_var)
+				} else {
+					g.expr(expr)
+				}
 				g.write(') ? _SLIT("nil") : ')
 			}
 		}
@@ -155,7 +175,11 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 		if unwrap_option {
 			g.expr(expr)
 		} else {
-			g.expr_with_cast(expr, typ, typ)
+			if temp_var_needed {
+				g.write(tmp_var)
+			} else {
+				g.expr_with_cast(expr, typ, typ)
+			}
 		}
 
 		if is_shared {
diff --git a/vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.out b/vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.out
new file mode 100644
index 000000000..f01a73fdd
--- /dev/null
+++ b/vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.out
@@ -0,0 +1,4 @@
+It should be printed only once
+&Abc{
+    s: ''
+}
diff --git a/vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.vv b/vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.vv
new file mode 100644
index 000000000..20c6fbbcf
--- /dev/null
+++ b/vlib/v/gen/c/testdata/gen_expr_to_string_with_call_and_return_ref.vv
@@ -0,0 +1,18 @@
+// for issue 20282
+// Phenomenon of issue:
+// When the expression is CallExpr and the return type is a pointer, cgen generates 2 actual call actions:
+// V code: println(call_test())
+// C code:
+// println(str_intp(1, _MOV((StrIntpData[]){{_SLIT("&"), 0xfe10 ,{.d_s = isnil(call_test()) ? _SLIT("nil") : string_str(*call_test())}}})));
+struct Abc {
+	s string
+}
+
+fn str_gen_with_call_and_return_ref() &Abc {
+	println('It should be printed only once')
+	return &Abc{}
+}
+
+fn main() {
+	println(str_gen_with_call_and_return_ref())
+}
-- 
2.39.5