From 334b66b311ea071d8ad4dec955f823e6caa7ff5d Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Sun, 17 Jan 2021 20:48:07 +0530
Subject: [PATCH] checker/cgen: add checks and fix cgen for [typedef] for C
 structs (#8169)

---
 vlib/math/big/big.v                                |  1 -
 vlib/v/checker/checker.v                           |  5 +++++
 vlib/v/checker/tests/typedef_attr_v_struct_err.out |  6 ++++++
 vlib/v/checker/tests/typedef_attr_v_struct_err.vv  |  7 +++++++
 vlib/v/gen/cgen.v                                  | 10 +++++++++-
 5 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 vlib/v/checker/tests/typedef_attr_v_struct_err.out
 create mode 100644 vlib/v/checker/tests/typedef_attr_v_struct_err.vv

diff --git a/vlib/math/big/big.v b/vlib/math/big/big.v
index 055dc14c28..24745223c4 100644
--- a/vlib/math/big/big.v
+++ b/vlib/math/big/big.v
@@ -4,7 +4,6 @@ module big
 #flag -I @VROOT/thirdparty/bignum
 #flag @VROOT/thirdparty/bignum/bn.o
 #include "bn.h"
-[typedef]
 struct C.bn {
 mut:
 	array [32]u32
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 52e8fc3b90..8e980b0290 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -387,6 +387,11 @@ pub fn (mut c Checker) struct_decl(mut decl ast.StructDecl) {
 				c.error('`$embed_sym.name` is not a struct', embed.pos)
 			}
 		}
+		for attr in decl.attrs {
+			if attr.name == 'typedef' && decl.language != .c {
+				c.error('`typedef` attribute can only be used with C structs', decl.pos)
+			}
+		}
 		for i, field in decl.fields {
 			if decl.language == .v {
 				c.check_valid_snake_case(field.name, 'field name', field.pos)
diff --git a/vlib/v/checker/tests/typedef_attr_v_struct_err.out b/vlib/v/checker/tests/typedef_attr_v_struct_err.out
new file mode 100644
index 0000000000..0253fba138
--- /dev/null
+++ b/vlib/v/checker/tests/typedef_attr_v_struct_err.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/typedef_attr_v_struct_err.vv:2:1: error: `typedef` attribute can only be used with C structs
+    1 | [typedef]
+    2 | struct Point{}
+      | ~~~~~~~~~~~~
+    3 | 
+    4 | fn main() {
diff --git a/vlib/v/checker/tests/typedef_attr_v_struct_err.vv b/vlib/v/checker/tests/typedef_attr_v_struct_err.vv
new file mode 100644
index 0000000000..421b635aaf
--- /dev/null
+++ b/vlib/v/checker/tests/typedef_attr_v_struct_err.vv
@@ -0,0 +1,7 @@
+[typedef]
+struct Point{}
+
+fn main() {
+    p := Point{}
+    println(p)
+}
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index f88e32c259..300c5c9e6f 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -660,7 +660,15 @@ typedef struct {
 			.alias {
 				parent := unsafe { &g.table.types[typ.parent_idx] }
 				is_c_parent := parent.name.len > 2 && parent.name[0] == `C` && parent.name[1] == `.`
-				parent_styp := if is_c_parent { 'struct ' + parent.cname[3..] } else { parent.cname }
+				mut is_typedef := false
+				if parent.info is table.Struct {
+					is_typedef = parent.info.is_typedef
+				}
+				parent_styp := if is_c_parent {
+					if !is_typedef { 'struct ' + parent.cname[3..] } else { parent.cname[3..] }
+				} else {
+					parent.cname
+				}
 				g.type_definitions.writeln('typedef $parent_styp $typ.cname;')
 			}
 			.array {