refactor: new direction for error reporting

src/error_tests.zig

@@ -0,0 +1,37 @@
+const std = @import("std");
+const Compilation = @import("compile.zig").Compilation;
+
+test "compiler: global variable shadowing" {
+    try testEqual(
+        \\VAR a = 0
+        \\VAR b = 2
+        \\VAR a = 1
+    ,
+        \\<STDIN>:3:1: error: redefined identifier
+        \\3    | VAR a = 1
+        \\     | ^
+        \\
+        ,
+    );
+}
+
+fn testEqual(source_bytes: [:0]const u8, expected_error: []const u8) !void {
+    const gpa = std.testing.allocator;
+    var allocating = std.io.Writer.Allocating.init(gpa);
+    defer allocating.deinit();
+    const io_w = &allocating.writer;
+
+    var c = try Compilation.compile(gpa, .{
+        .source_bytes = source_bytes,
+        .filename = "<STDIN>",
+        .dump_writer = null,
+        .dump_use_color = false,
+        .dump_ast = false,
+        .dump_ir = false,
+    });
+    defer c.deinit();
+
+    try std.testing.expect(c.errors.len > 0);
+    for (c.errors) |err| try c.renderError(io_w, err);
+    return std.testing.expectEqualSlices(u8, expected_error, allocating.written());
+}