// Tests for imports.zig — flat-import name-resolution data retention (fix-0102a).

const std = @import("std");
const ast = @import("ast.zig");
const parser = @import("parser.zig");
const imports = @import("imports.zig");
const errors = @import("errors.zig");

var g_test_threaded: ?std.Io.Threaded = null;
fn testIo() std.Io {
    if (g_test_threaded == null) {
        g_test_threaded = std.Io.Threaded.init(std.heap.page_allocator, .{});
    }
    return g_test_threaded.?.io();
}

// ── buildImportFacts unit tests (Phase A: import-side raw facts) ──

const Facts = struct {
    decls: imports.ModuleDecls,
    ns_edges: imports.NamespaceEdges,
    diags: errors.DiagnosticList,
};

/// Parse `main_path`, resolve its imports, then build the raw import facts —
/// the exact path `core.zig` drives. `alloc` must be an arena that outlives the
/// returned views (they point into AST + cache memory it owns).
fn buildFacts(alloc: std.mem.Allocator, io: std.Io, absdir: []const u8, main_path: []const u8) !Facts {
    const main_bytes = try std.Io.Dir.readFileAlloc(.cwd(), io, main_path, alloc, .limited(1 << 20));
    const main_source = try alloc.dupeZ(u8, main_bytes);
    var p = parser.Parser.init(alloc, main_source);
    const root = p.parse() catch return error.ParseFailed;

    var diags = errors.DiagnosticList.init(alloc, main_source, main_path);
    var chain = std.StringHashMap(void).init(alloc);
    var cache = imports.ModuleCache.init(alloc);
    var import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
    var flat_import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
    const stdlib_paths = [_][]const u8{};

    const mod = try imports.resolveImports(
        alloc,
        io,
        root,
        absdir,
        main_path,
        &chain,
        &cache,
        null,
        &diags,
        &stdlib_paths,
        &import_graph,
        &flat_import_graph,
        .{},
    );

    const facts = try imports.buildImportFacts(alloc, main_path, mod, &cache);
    return .{ .decls = facts.decls, .ns_edges = facts.ns_edges, .diags = diags };
}

fn expectTag(ref: imports.RawDeclRef, expected: std.meta.Tag(imports.RawDeclRef)) !void {
    try std.testing.expectEqual(expected, std.meta.activeTag(ref));
}

fn hasErr(diags: *const errors.DiagnosticList, needle: []const u8) bool {
    for (diags.items.items) |d| {
        if (d.level == .err and std.mem.indexOf(u8, d.message, needle) != null) return true;
    }
    return false;
}

// Two flat-imported modules each author `greet`; a third is namespaced. The
// step retains BOTH `greet` authors under their own paths in `module_fns` and
// records the namespaced import in `import_graph` but NOT in `flat_import_graph`
// — WITHOUT touching the merged scope: `mod.decls` stays byte-for-byte
// first-wins (one `greet`, a.sx's), exactly as on `wt-fix-0102-base`.
test "imports: module_fns retains same-name cross-module fns; flat_import_graph excludes namespaced edge" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "a.sx", .data = "greet :: () -> s64 { 1 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "b.sx", .data = "greet :: () -> s64 { 2 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "nsmod.sx", .data = "helper :: () -> s64 { 3 }\n" });
    const main_src =
        \\#import "a.sx";
        \\#import "b.sx";
        \\ns :: #import "nsmod.sx";
        \\main :: () -> s32 { 0 }
        \\
    ;
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = main_src });

    var dirbuf: [4096]u8 = undefined;
    const dirlen = try tmp.dir.realPath(io, &dirbuf);
    const absdir = dirbuf[0..dirlen];

    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});
    const a_path = try std.fmt.allocPrint(alloc, "{s}/a.sx", .{absdir});
    const b_path = try std.fmt.allocPrint(alloc, "{s}/b.sx", .{absdir});
    const ns_path = try std.fmt.allocPrint(alloc, "{s}/nsmod.sx", .{absdir});

    const main_bytes = try std.Io.Dir.readFileAlloc(.cwd(), io, main_path, alloc, .limited(1 << 20));
    const main_source = try alloc.dupeZ(u8, main_bytes);
    var p = parser.Parser.init(alloc, main_source);
    const root = p.parse() catch return error.ParseFailed;

    var chain = std.StringHashMap(void).init(alloc);
    var cache = imports.ModuleCache.init(alloc);
    var import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
    var flat_import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
    const stdlib_paths = [_][]const u8{};

    const mod = try imports.resolveImports(
        alloc,
        io,
        root,
        absdir,
        main_path,
        &chain,
        &cache,
        null,
        null,
        &stdlib_paths,
        &import_graph,
        &flat_import_graph,
        .{},
    );

    var module_fns = imports.ModuleFns.init(alloc);
    try imports.buildModuleFns(alloc, main_path, mod, &cache, &module_fns);

    // The MERGED scope the first-wins resolver consumes is unchanged: mergeFlat
    // still drops the second `greet`, so `mod.decls` carries exactly ONE — and
    // it is a.sx's author (the first flat import), not b.sx's.
    var greet_count: usize = 0;
    var merged_greet: ?*const ast.FnDecl = null;
    for (mod.decls) |decl| {
        const name = decl.data.declName() orelse continue;
        if (!std.mem.eql(u8, name, "greet")) continue;
        greet_count += 1;
        if (decl.data == .fn_decl) merged_greet = &decl.data.fn_decl;
    }
    try std.testing.expectEqual(@as(usize, 1), greet_count);

    // module_fns retains BOTH authors of `greet`, keyed by their own paths —
    // the dropped author is recorded here (side index), not in the merged scope.
    const a_fns = module_fns.get(a_path) orelse return error.MissingAFns;
    const b_fns = module_fns.get(b_path) orelse return error.MissingBFns;
    const a_greet = a_fns.get("greet") orelse return error.MissingAGreet;
    const b_greet = b_fns.get("greet") orelse return error.MissingBGreet;
    // Distinct authoring decls — not the same node deduped down to one.
    try std.testing.expect(a_greet != b_greet);
    // First-wins: the surviving merged-scope `greet` is a.sx's author.
    try std.testing.expect(merged_greet == a_greet);

    // flat_import_graph carries the two bare `#import` edges, NOT the
    // namespaced `ns :: #import` edge.
    const flat = flat_import_graph.get(main_path) orelse return error.MissingFlatEdges;
    try std.testing.expect(flat.contains(a_path));
    try std.testing.expect(flat.contains(b_path));
    try std.testing.expect(!flat.contains(ns_path));

    // The full import_graph DOES record the namespaced edge (the contrast that
    // makes the flat-graph exclusion meaningful).
    const full = import_graph.get(main_path) orelse return error.MissingFullEdges;
    try std.testing.expect(full.contains(a_path));
    try std.testing.expect(full.contains(b_path));
    try std.testing.expect(full.contains(ns_path));
}

// Mixed collision: a.sx authors `Widget` as a STRUCT (non-fn), b.sx authors it
// as a FUNCTION. fix-0102a must NOT let the function-author retention shift the
// merged scope — first-wins keeps a.sx's struct and drops b.sx's function,
// exactly as on `wt-fix-0102-base`. (The fn author may still be indexed in
// module_fns; resolution is what must be untouched.)
test "imports: mixed non-fn/fn same-name collision stays first-wins in merged scope" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "a.sx", .data = "Widget :: struct { x: s64 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "b.sx", .data = "Widget :: () -> s64 { 7 }\n" });
    const main_src =
        \\#import "a.sx";
        \\#import "b.sx";
        \\main :: () -> s32 { 0 }
        \\
    ;
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = main_src });

    var dirbuf: [4096]u8 = undefined;
    const dirlen = try tmp.dir.realPath(io, &dirbuf);
    const absdir = dirbuf[0..dirlen];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});

    const main_bytes = try std.Io.Dir.readFileAlloc(.cwd(), io, main_path, alloc, .limited(1 << 20));
    const main_source = try alloc.dupeZ(u8, main_bytes);
    var p = parser.Parser.init(alloc, main_source);
    const root = p.parse() catch return error.ParseFailed;

    var chain = std.StringHashMap(void).init(alloc);
    var cache = imports.ModuleCache.init(alloc);
    var import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
    var flat_import_graph = std.StringHashMap(std.StringHashMap(void)).init(alloc);
    const stdlib_paths = [_][]const u8{};

    const mod = try imports.resolveImports(
        alloc,
        io,
        root,
        absdir,
        main_path,
        &chain,
        &cache,
        null,
        null,
        &stdlib_paths,
        &import_graph,
        &flat_import_graph,
        .{},
    );

    // Exactly ONE `Widget` survives the merged scope, and it is a.sx's STRUCT —
    // the function author did not displace or duplicate it.
    var widget_count: usize = 0;
    var merged_is_struct = false;
    for (mod.decls) |decl| {
        const name = decl.data.declName() orelse continue;
        if (!std.mem.eql(u8, name, "Widget")) continue;
        widget_count += 1;
        merged_is_struct = decl.data == .struct_decl;
    }
    try std.testing.expectEqual(@as(usize, 1), widget_count);
    try std.testing.expect(merged_is_struct);
}

// Flat imports: each module's authored decls land in ITS OWN scalar index keyed
// by path. Two modules authoring the same `fn`, the same `struct`, and a
// value-vs-type same spelling are ALL retained per-source — no cross-module
// first-wins at the index level. A `const_decl` is stored raw (`.const_decl`),
// not pre-classified into value/fn.
test "buildImportFacts: flat imports keep same-name fn/struct + value-vs-type per source; const stays raw" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    // a.sx: dup() fn, Box struct, Shape as a VALUE const.
    try tmp.dir.writeFile(io, .{ .sub_path = "a.sx", .data = "dup :: () -> s64 { 1 }\nBox :: struct { x: s64 }\nShape :: 7;\n" });
    // b.sx: dup() fn, Box struct, Shape as a TYPE (same spelling as a.sx's value).
    try tmp.dir.writeFile(io, .{ .sub_path = "b.sx", .data = "dup :: () -> s64 { 2 }\nBox :: struct { y: s64 }\nShape :: struct { z: s64 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "#import \"a.sx\";\n#import \"b.sx\";\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});
    const a_path = try std.fmt.allocPrint(alloc, "{s}/a.sx", .{absdir});
    const b_path = try std.fmt.allocPrint(alloc, "{s}/b.sx", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    const a_idx = facts.decls.get(a_path) orelse return error.MissingAIndex;
    const b_idx = facts.decls.get(b_path) orelse return error.MissingBIndex;
    const m_idx = facts.decls.get(main_path) orelse return error.MissingMainIndex;

    // The index records its own source path.
    try std.testing.expectEqualStrings(a_path, a_idx.source);

    // main authors `main` as a fn.
    try expectTag(m_idx.names.get("main") orelse return error.MissingMain, .fn_decl);

    // Same-name fn retained per source — two DISTINCT FnDecls.
    const a_dup = a_idx.names.get("dup") orelse return error.MissingADup;
    const b_dup = b_idx.names.get("dup") orelse return error.MissingBDup;
    try expectTag(a_dup, .fn_decl);
    try expectTag(b_dup, .fn_decl);
    try std.testing.expect(a_dup.fn_decl != b_dup.fn_decl);

    // Same-name struct retained per source — two DISTINCT StructDecls.
    const a_box = a_idx.names.get("Box") orelse return error.MissingABox;
    const b_box = b_idx.names.get("Box") orelse return error.MissingBBox;
    try expectTag(a_box, .struct_decl);
    try expectTag(b_box, .struct_decl);
    try std.testing.expect(a_box.struct_decl != b_box.struct_decl);

    // Value-vs-type same spelling across modules: a.sx's `Shape` is a raw const
    // (NOT pre-classified), b.sx's `Shape` is a struct. Both coexist by source.
    try expectTag(a_idx.names.get("Shape") orelse return error.MissingAShape, .const_decl);
    try expectTag(b_idx.names.get("Shape") orelse return error.MissingBShape, .struct_decl);

    // No spurious diagnostics — these are distinct files, not same-module dups.
    try std.testing.expect(!hasErr(&facts.diags, "duplicate top-level"));
}

// Directory import: the combined module (keyed by the directory path) carries
// the UNION of every file's authored decls in its scalar index.
test "buildImportFacts: directory import unions member-file decls under the dir path" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.createDirPath(io, "lib");
    try tmp.dir.writeFile(io, .{ .sub_path = "lib/one.sx", .data = "from_one :: () -> s64 { 1 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "lib/two.sx", .data = "Two :: struct { v: s64 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "#import \"lib\";\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});
    const lib_path = try std.fmt.allocPrint(alloc, "{s}/lib", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    const lib_idx = facts.decls.get(lib_path) orelse return error.MissingLibIndex;
    try expectTag(lib_idx.names.get("from_one") orelse return error.MissingFromOne, .fn_decl);
    try expectTag(lib_idx.names.get("Two") orelse return error.MissingTwo, .struct_decl);
}

// Namespaced file import (`g :: #import "point.sx"`): recorded as a namespace
// edge whose `target_module_path` is the aliased file (the fact lost today),
// AND as a `.namespace_decl` in the importer's scalar index.
test "buildImportFacts: namespaced file import captures target_module_path" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "point.sx", .data = "Point :: struct { x: s64 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "g :: #import \"point.sx\";\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});
    const point_path = try std.fmt.allocPrint(alloc, "{s}/point.sx", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    const main_edges = facts.ns_edges.get(main_path) orelse return error.MissingMainEdges;
    const g = main_edges.get("g") orelse return error.MissingGEdge;
    try std.testing.expectEqualStrings("g", g.alias);
    try std.testing.expectEqualStrings(main_path, g.importer_source);
    try std.testing.expectEqualStrings(point_path, g.target_module_path);
    try std.testing.expect(g.own_decls.len >= 1);
    try std.testing.expect(!g.is_pub);

    // The alias is also a `.namespace_decl` in the importer's scalar index.
    const m_idx = facts.decls.get(main_path) orelse return error.MissingMainIndex;
    try expectTag(m_idx.names.get("g") orelse return error.MissingGRef, .namespace_decl);
}

// Namespaced directory import: same edge capture, target is the directory path.
test "buildImportFacts: namespaced directory import captures dir path as target" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.createDirPath(io, "pkg");
    try tmp.dir.writeFile(io, .{ .sub_path = "pkg/m.sx", .data = "helper :: () -> s64 { 9 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "pkg :: #import \"pkg\";\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});
    const pkg_path = try std.fmt.allocPrint(alloc, "{s}/pkg", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    const main_edges = facts.ns_edges.get(main_path) orelse return error.MissingMainEdges;
    const pkg = main_edges.get("pkg") orelse return error.MissingPkgEdge;
    try std.testing.expectEqualStrings(pkg_path, pkg.target_module_path);
}

// C-import namespace (`c :: #import c { #include ... }`): recorded as a namespace
// edge. With no separate sx module, the target is the importing file itself.
test "buildImportFacts: c-import namespace recorded as an edge" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "ch.h", .data = "int cm_add(int a, int b);\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "cmod :: #import c {\n    #include \"ch.h\";\n};\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    const main_edges = facts.ns_edges.get(main_path) orelse return error.MissingMainEdges;
    const cmod = main_edges.get("cmod") orelse return error.MissingCmodEdge;
    try std.testing.expectEqualStrings("cmod", cmod.alias);
    try std.testing.expectEqualStrings(main_path, cmod.target_module_path);

    const m_idx = facts.decls.get(main_path) orelse return error.MissingMainIndex;
    try expectTag(m_idx.names.get("cmod") orelse return error.MissingCmodRef, .namespace_decl);
}

// Duplicate-name invariant (R5 #2): a same-module authored duplicate top-level
// name is DIAGNOSED, not silently dropped. The parser/decl-checker does not
// catch this today (verified: `sx run` of a same-file double decl exits 0 with
// no diagnostic), so `resolveImports` surfaces it where `addOwnDecl` refuses the
// second author. This test FAILS on the pre-diagnostic code and PASSES after.
test "buildImportFacts: same-module duplicate top-level name is diagnosed" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "foo :: () -> s64 { 1 }\nfoo :: () -> s64 { 2 }\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    try std.testing.expect(hasErr(&facts.diags, "duplicate top-level declaration 'foo'"));
    // The surviving author is still in the scalar index (first-wins, not lost).
    const m_idx = facts.decls.get(main_path) orelse return error.MissingMainIndex;
    try expectTag(m_idx.names.get("foo") orelse return error.MissingFoo, .fn_decl);
}

// F1: the duplicate-name invariant must also cover NAMESPACE ALIASES. A
// `dup :: #import "…"` alias colliding with a same-module authored name is a
// duplicate in EITHER order — `addNamespace` (alias second) and `addOwnDecl`
// (alias first) each refuse the second author and the site diagnoses it. Before
// the fix the fn-then-alias order compiled clean (silent first-win in the scalar
// index). Surviving author is whichever came FIRST.
test "buildImportFacts: fn-then-namespace-alias same-module collision is diagnosed" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "lib.sx", .data = "helper :: () -> s64 { 9 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "dup :: () -> s64 { 1 }\ndup :: #import \"lib.sx\";\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    try std.testing.expect(hasErr(&facts.diags, "duplicate top-level declaration 'dup'"));
    // The fn came first, so it survives in the scalar index; the alias dropped.
    const m_idx = facts.decls.get(main_path) orelse return error.MissingMainIndex;
    try expectTag(m_idx.names.get("dup") orelse return error.MissingDup, .fn_decl);
}

test "buildImportFacts: namespace-alias-then-fn same-module collision is diagnosed" {
    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arena.deinit();
    const alloc = arena.allocator();
    const io = testIo();

    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    try tmp.dir.writeFile(io, .{ .sub_path = "lib.sx", .data = "helper :: () -> s64 { 9 }\n" });
    try tmp.dir.writeFile(io, .{ .sub_path = "main.sx", .data = "dup :: #import \"lib.sx\";\ndup :: () -> s64 { 1 }\nmain :: () -> s32 { 0 }\n" });

    var dirbuf: [4096]u8 = undefined;
    const absdir = dirbuf[0..try tmp.dir.realPath(io, &dirbuf)];
    const main_path = try std.fmt.allocPrint(alloc, "{s}/main.sx", .{absdir});

    var facts = try buildFacts(alloc, io, absdir, main_path);

    try std.testing.expect(hasErr(&facts.diags, "duplicate top-level declaration 'dup'"));
    // The alias came first, so the namespace_decl survives; the fn dropped.
    const m_idx = facts.decls.get(main_path) orelse return error.MissingMainIndex;
    try expectTag(m_idx.names.get("dup") orelse return error.MissingDup, .namespace_decl);
}