Add logs for std.zig.Ast.parse() failure

[tiawl]

Hi,

As stated by this pull request title, it just provides some logs when std.zig.Ast.parse() failed to avoid some potential headaches.

Here a demo of the output:

cons std = @import ("std");
const fmt = std.fmt;
const allocPrint = fmt.allocPrint

fn main () void
{
  var i: u32 = 0;
  i++;
  const j: v32 = undefined,
  _ = j;
}

ERROR: zig.Ast.Error{ .tag = zig.Ast.Error.Tag.expected_comma_after_field, .is_note = false, .token_is_prev = false, .token = 1, .extra = zig.Ast.Error.Error__union_6445@7ffe2d1231c0 }
TOKEN: zig.tokenizer.Token{ .tag = zig.tokenizer.Token.Tag.identifier, .loc = zig.tokenizer.Token.Loc{ .start = 0, .end = 4 } }

cons std = @import ("std");
^^^^
ERROR: zig.Ast.Error{ .tag = zig.Ast.Error.Tag.expected_semi_after_decl, .is_note = false, .token_is_prev = true, .token = 20, .extra = zig.Ast.Error.Error__union_6445@7ffe2d1231c0 }
TOKEN: zig.tokenizer.Token{ .tag = zig.tokenizer.Token.Tag.period, .loc = zig.tokenizer.Token.Loc{ .start = 71, .end = 72 } }

const allocPrint = fmt.allocPrint
                      ^
ERROR: zig.Ast.Error{ .tag = zig.Ast.Error.Tag.expected_expr, .is_note = false, .token_is_prev = false, .token = 36, .extra = zig.Ast.Error.Error__union_6445@7ffe2d1231c0 }
TOKEN: zig.tokenizer.Token{ .tag = zig.tokenizer.Token.Tag.plus_plus, .loc = zig.tokenizer.Token.Loc{ .start = 123, .end = 125 } }

  i++;
   ^^
ERROR: zig.Ast.Error{ .tag = zig.Ast.Error.Tag.expected_statement, .is_note = false, .token_is_prev = false, .token = 43, .extra = zig.Ast.Error.Error__union_6445@7ffe2d1231c0 }
TOKEN: zig.tokenizer.Token{ .tag = zig.tokenizer.Token.Tag.identifier, .loc = zig.tokenizer.Token.Loc{ .start = 144, .end = 153 } }

  const j: v32 = undefined,
                 ^^^^^^^^^
thread 13107 panic: reached unreachable code
/home/user/.local/bin/lib/std/debug.zig:343:14: 0x2f0bf2 in assert (build)
    if (!ok) unreachable; // assertion failure
             ^
/home/user/Workspace/vulkan-zig/generator/vulkan/build_integration.zig:190:25: 0x389b83 in make (build)
        std.debug.assert(tree.errors.len == 0); // If this triggers, vulkan-zig produced invalid code.
                        ^

It is maybe not totally accurate but it gives a not so bad idea where is the potential mistakes in the generated content.

Hope it could help.

[Snektron]

Thanks, that should be useful during development. I wonder, what prompted you to add this?

[tiawl]

I am working on a very similar tool so I am currently reading, copying and pasting some huge parts of your code. I was very frustrated that this necessary assertion did not output more logging data about generated code (specially when it contains thousands of lines). Because I copied and I spent time to understand this part of your code, add useful code in mine should accordingly be useful for your code too. Now you know the all story.

Reading the code I submitted, some parts could be improved:

• replace var tokens = try std.ArrayList (std.zig.Ast.Error).initCapacity (b.allocator, tree.errors.len); with var tokens: [] std.zig.Ast.Error = @constCast (tree.errors); will avoid unnecessary heap usage,
• refactor this:

repeat = 1;
spaces = "";
while (repeat < current_token.loc.start - start)
{
  spaces = try std.fmt.allocPrint (b.allocator, "{s} ", .{ spaces, });
  repeat += 1;
}

  into a fn runtime_repeat (allocator: std.mem.Allocator, char: u8, repeat: usize) ![] const u8 will shorten the code and improve the readability.

Do I make another pull request to submit this changes ?