v2: fix arm64 self-hosting (#27396)

Author: medvednikov

vlib/v2/ast/flat.v

@@ -165,3 +165,46 @@ fn test_append_flat_empty_source_is_noop() {
 	assert dst.flat.edges.len == pre_edges
 	assert dst.flat.files.len == pre_files
 }
+
+fn test_copy_subtree_from_preserves_stmt_shape_and_strings() {
+	mut src := new_flat_builder()
+	imp_id := src.emit_stmt(Stmt(ImportStmt{
+		name:       'os'
+		alias:      'myos'
+		is_aliased: true
+	}))
+	dir_id := src.emit_stmt(Stmt(Directive{
+		name:  'flag'
+		value: '-lm'
+	}))
+	for_id := src.emit_stmt(make_for_with_idents(['alpha', 'beta']))
+
+	mut dst := seeded_dst()
+	copied_imp := dst.copy_subtree_from(&src.flat, imp_id)
+	copied_dir := dst.copy_subtree_from(&src.flat, dir_id)
+	copied_for := dst.copy_subtree_from(&src.flat, for_id)
+
+	assert dst.flat.subtree_signature(copied_for) == src.flat.subtree_signature(for_id)
+
+	merged_imp := Cursor{
+		flat: &dst.flat
+		id:   copied_imp
+	}.stmt() as ImportStmt
+	assert merged_imp.name == 'os'
+	assert merged_imp.alias == 'myos'
+	assert merged_imp.is_aliased
+
+	merged_dir := Cursor{
+		flat: &dst.flat
+		id:   copied_dir
+	}.stmt() as Directive
+	assert merged_dir.name == 'flag'
+	assert merged_dir.value == '-lm'
+}
+
+fn test_copy_subtree_from_invalid_root_returns_invalid() {
+	mut src := new_flat_builder()
+	mut dst := new_flat_builder()
+	assert dst.copy_subtree_from(&src.flat, -1) == invalid_flat_node_id
+	assert dst.copy_subtree_from(&src.flat, 100) == invalid_flat_node_id
+}

vlib/v2/ast/flat_append_flat_test.v

@@ -285,14 +285,9 @@ pub fn (mut b Builder) build(files []string) {
 		}
 	} else {
 		// Parallel transform fans the per-file work across worker threads via
-		// the driver, then flattens. The sequential transform_flat_to_flat_direct
-		// is ~3x slower here because it cannot parallelize the per-file loop, and
-		// the flat AST has no thread-safe merge primitive to let workers append
-		// to one builder concurrently. For flat-codegen backends we still drop
-		// b.files immediately so codegen stays flat-only (the legacy files are
-		// live only transiently during the parallel transform). The memory-
-		// critical arm64 self-host runs --no-parallel, so it takes the sequential
-		// branch above and keeps the allocation-minimal flat-direct path.
+		// the driver. Flat-codegen backends use worker-local FlatBuilders merged
+		// by append_flat and keep b.files empty; legacy consumers request the
+		// compatibility []ast.File result.
 		new_flat, files_out := b.transform_files_parallel_to_flat_via_driver(mut trans,
 			!transform_flat_only)
 		b.flat = new_flat

vlib/v2/builder/builder.v

@@ -882,8 +882,8 @@ fn (l Linker) generate_code_signature(ident string) []u8 {
 	// Slot -2: Hash of requirements blob
 	mut hash_buf := [32]u8{}
 	sha256_hash(req_blob.data, req_blob.len, &hash_buf[0])
-	for b in hash_buf {
-		sig << b
+	for i in 0 .. cs_hash_size {
+		sig << hash_buf[i]
 	}
 
 	// Slot -1: Info.plist (zeros = no Info.plist)

vlib/v2/gen/arm64/linker.v

@@ -0,0 +1,29 @@
+import v2.ast
+
+fn main() {
+	file := ast.File{
+		name:    @FILE
+		mod:     'main'
+		imports: [
+			ast.ImportStmt{
+				name:  'v2.pref'
+				alias: 'pref'
+			},
+		]
+		stmts:   [
+			ast.Stmt(ast.ImportStmt{
+				name:  'v2.pref'
+				alias: 'pref'
+			}),
+		]
+	}
+	flat := ast.flatten_files([file])
+	file_node := flat.nodes[flat.files[0].file_id]
+	imports := flat.read_file_imports(flat.files[0])
+	println(file_node.edge_count)
+	println(imports.len)
+	if imports.len > 0 {
+		println(imports[0].name)
+		println(imports[0].alias)
+	}
+}

vlib/v2/gen/arm64/tests/flat_ast_import_edges.v

@@ -0,0 +1,18 @@
+fn push_name(mut names []string, name string) {
+	names << name
+	println(names.len)
+}
+
+fn wrap(mut names []string, name string) {
+	push_name(mut names, name)
+	println(names.len)
+}
+
+fn main() {
+	mut names := []string{}
+	wrap(mut names, 'abc')
+	println(names.len)
+	if names.len > 0 {
+		println(names[0])
+	}
+}