Async recursion with comptime arguments causes compiler assertion failure

[fengb]

I'm not sure how to explain it but here's a minimal repro:

pub fn format(comptime fmt: []const u8, args: var) void {
    suspend; // commenting this out works
    inline for (fmt) |c| {
        switch (c) {
            'c' => formatType(args[0], "c"),
            else => formatType(args[0], ""),
        }
    }
}

pub fn formatType(value: var, comptime fmt: []const u8) void {
    if (fmt.len > 0 and fmt[0] == 'c') {
        // return formatType(value, ""); // replacing the bottom line with this works
        return format("}", .{value});
    }
}

test "kablamo" {
    // const value = 'a'; // replacing the bottom line with this works
    const value: u8 = 'a';
    _ = async format("c", .{value});
}

Assertion failed at ~/projects/zig/src/analyze.cpp:9037 in resolve_llvm_types. This is a bug in the Zig compiler.
Unable to dump stack trace: debug info stripped
Aborted

[fengb]

Might be related to #4063

[andrewrk]

Slightly more simplified:

pub fn format(comptime fmt: u8, args: var) void {
    suspend; // commenting this out works
    switch (fmt) {
        'c' => formatType(args[0], 'c'),
        else => formatType(args[0], '_'),
    }
}

pub fn formatType(value: var, comptime fmt: u8) void {
    if (fmt == 'c') {
        return format('}', .{value});
    }
}

test "kablamo" {
    // const value = 'a'; // replacing the bottom line with this works
    const value: u8 = 'a';
    _ = async format('c', .{value});
}

Here's a new (earlier) assert that trips:

--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -6386,6 +6386,8 @@ static Error resolve_async_frame(CodeGen *g, ZigType *frame_type) {
         }
         instruction->field_index = fields.length;
 
+        src_assert(child_type->id != ZigTypeIdPointer || child_type->data.pointer.inferred_struct_field == nullptr,
+                instruction->base.source_node);
         fields.append({name, child_type, instruction->align});
     }

when analyzing /home/andy/dev/zig/build/test.zig:11:30: assertion failed. This is a bug in the Zig compiler.

Appears that the spill of args to the @Frame of formatType was given a type that isn't supposed to be able to escape struct type inference.

[andrewrk]

Further simplification:

fn asyncArgs(args: var) void {
    suspend;
}

fn foo(value: u8) void {
    return asyncArgs(.{value});
}

test "kablamo" {
    _ = async foo('a');
}

[fengb]

Fixed by #4110