From 7a51e0befe12c9d17e39f736027a205b1f19bdc6 Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Fri, 2 Sep 2022 14:59:06 +0300
Subject: [PATCH] Sema: fix noalias coercion error message

Closes #11769
---
 src/Sema.zig                                  |  9 ++++++---
 src/type.zig                                  |  3 +++
 .../compile_errors/noalias_param_coersion.zig | 20 +++++++++++++++++++
 3 files changed, 29 insertions(+), 3 deletions(-)
 create mode 100644 test/cases/compile_errors/noalias_param_coersion.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index c089794fa9..a49aec871b 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -23426,8 +23426,11 @@ const InMemoryCoercionResult = union(enum) {
                 var index: u6 = 0;
                 var actual_noalias = false;
                 while (true) : (index += 1) {
-                    if (param.actual << index != param.wanted << index) {
-                        actual_noalias = (param.actual << index) == (1 << 31);
+                    const actual = @truncate(u1, param.actual >> index);
+                    const wanted = @truncate(u1, param.wanted >> index);
+                    if (actual != wanted) {
+                        actual_noalias = actual == 1;
+                        break;
                     }
                 }
                 if (!actual_noalias) {
@@ -23921,7 +23924,7 @@ fn coerceInMemoryAllowedFns(
 
     if (dest_info.noalias_bits != src_info.noalias_bits) {
         return InMemoryCoercionResult{ .fn_param_noalias = .{
-            .actual = dest_info.noalias_bits,
+            .actual = src_info.noalias_bits,
             .wanted = dest_info.noalias_bits,
         } };
     }
diff --git a/src/type.zig b/src/type.zig
index 339485c137..59e9b163d9 100644
--- a/src/type.zig
+++ b/src/type.zig
@@ -2042,6 +2042,9 @@ pub const Type = extern union {
                 try writer.writeAll("fn(");
                 for (fn_info.param_types) |param_ty, i| {
                     if (i != 0) try writer.writeAll(", ");
+                    if (std.math.cast(u5, i)) |index| if (@truncate(u1, fn_info.noalias_bits >> index) != 0) {
+                        try writer.writeAll("noalias ");
+                    };
                     if (param_ty.tag() == .generic_poison) {
                         try writer.writeAll("anytype");
                     } else {
diff --git a/test/cases/compile_errors/noalias_param_coersion.zig b/test/cases/compile_errors/noalias_param_coersion.zig
new file mode 100644
index 0000000000..e6dfae0370
--- /dev/null
+++ b/test/cases/compile_errors/noalias_param_coersion.zig
@@ -0,0 +1,20 @@
+pub export fn entry() void {
+    comptime var x: fn (noalias *i32, noalias *i32) void = undefined;
+    x = bar;
+}
+pub export fn entry1() void {
+    comptime var x: fn (*i32, *i32) void = undefined;
+    x = foo;
+}
+
+fn foo(noalias _: *i32, noalias _: *i32) void {}
+fn bar(noalias _: *i32, _: *i32) void {}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:9: error: expected type 'fn(noalias *i32, noalias *i32) void', found 'fn(noalias *i32, *i32) void'
+// :3:9: note: regular parameter 1 cannot cast into a noalias parameter
+// :7:9: error: expected type 'fn(*i32, *i32) void', found 'fn(noalias *i32, noalias *i32) void'
+// :7:9: note: noalias parameter 0 cannot cast into a regular parameter