From 5b9c5191ab919f4166a9e0c4486bd57bb2533791 Mon Sep 17 00:00:00 2001
From: Jacob Young <jacobly0@users.noreply.github.com>
Date: Fri, 9 Sep 2022 02:28:56 -0400
Subject: [PATCH] type: print comptime on fn type params

This avoids the following confusing error message:

    error: expected type 'fn(i32, i32) void', found 'fn(i32, i32) void'
---
 src/type.zig                                  |  3 +++
 test/behavior/typename.zig                    |  4 ++--
 .../comptime_param_coersion.zig               | 20 +++++++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 test/cases/compile_errors/comptime_param_coersion.zig

diff --git a/src/type.zig b/src/type.zig
index 0d48c5e46a..ec7e155d4e 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 (fn_info.paramIsComptime(i)) {
+                        try writer.writeAll("comptime ");
+                    }
                     if (std.math.cast(u5, i)) |index| if (@truncate(u1, fn_info.noalias_bits >> index) != 0) {
                         try writer.writeAll("noalias ");
                     };
diff --git a/test/behavior/typename.zig b/test/behavior/typename.zig
index 3bc8c58389..63e36488e0 100644
--- a/test/behavior/typename.zig
+++ b/test/behavior/typename.zig
@@ -122,7 +122,7 @@ test "top level decl" {
     );
     // generic fn
     try expectEqualStrings(
-        "fn(type) type",
+        "fn(comptime type) type",
         @typeName(@TypeOf(TypeFromFn)),
     );
 }
@@ -244,5 +244,5 @@ test "comptime parameters not converted to anytype in function type" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
 
     const T = fn (fn (type) void, void) void;
-    try expectEqualStrings("fn(fn(type) void, void) void", @typeName(T));
+    try expectEqualStrings("fn(comptime fn(comptime type) void, void) void", @typeName(T));
 }
diff --git a/test/cases/compile_errors/comptime_param_coersion.zig b/test/cases/compile_errors/comptime_param_coersion.zig
new file mode 100644
index 0000000000..8441929249
--- /dev/null
+++ b/test/cases/compile_errors/comptime_param_coersion.zig
@@ -0,0 +1,20 @@
+pub export fn entry() void {
+    comptime var x: fn (comptime i32, comptime i32) void = undefined;
+    x = bar;
+}
+pub export fn entry1() void {
+    comptime var x: fn (i32, i32) void = undefined;
+    x = foo;
+}
+
+fn foo(comptime _: i32, comptime _: i32) void {}
+fn bar(comptime _: i32, _: i32) void {}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:9: error: expected type 'fn(comptime i32, comptime i32) void', found 'fn(comptime i32, i32) void'
+// :3:9: note: non-comptime parameter 1 cannot cast into a comptime parameter
+// :7:9: error: expected type 'fn(i32, i32) void', found 'fn(comptime i32, comptime i32) void'
+// :7:9: note: generic function cannot cast into a non-generic function