feat(parser): add struct initializer shorthand

Author: radovanhorvat

docs/overview/07-structs.md

@@ -29,6 +29,22 @@ c1.port = 3
 c1.host = "foo"
 ```
 
+When a visible value has the same name as a field, its field initializer may
+omit `= value`:
+
+```jik
+host := "localhost"
+port := 8080
+verbose := true
+
+c2 := Config{host, port, verbose}
+c3 := Config{host = "example.com", port, verbose}
+```
+
+`Config{host, port, verbose}` is exactly equivalent to
+`Config{host = host, port = port, verbose = verbose}`. These entries are always
+named, not positional: their order does not need to match the declaration order.
+
 Struct values can be read and updated through their fields using the usual `.` syntax.
 
 ### 7.3 Uniform function calls

src/jik/parser.c

@@ -1416,9 +1416,18 @@ jik_parser_parse_struct_new(JikParser *p, JikToken *struct_name_tok, char *modul
     TabJikNode *init_vals = TabJikNode_new();
     while ((tok = jik_parser_current_token(p)) != NULL && tok->type != TOK_RCURL) {
         jik_parser_eat_newlines_if_found(p);
-        char *field_name = jik_parser_eat_token(p, TOK_ID)->lexeme;
-        jik_parser_eat_token(p, TOK_ASSIGN);
-        JikNode *expr = jik_parser_parse_expr(p);
+        JikToken *field_tok  = jik_parser_eat_token(p, TOK_ID);
+        char     *field_name = field_tok->lexeme;
+        JikNode  *expr;
+        if (jik_parser_current_token(p)->type == TOK_ASSIGN) {
+            jik_parser_eat_token(p, TOK_ASSIGN);
+            expr = jik_parser_parse_expr(p);
+        }
+        else {
+            // Field shorthand: `Point{x}` is equivalent to `Point{x = x}`
+            expr = jik_node_new_identifier(
+                field_name, NULL, jik_parser_current_context(p), field_tok);
+        }
         jik_parser_eat_newlines_if_found(p);
         TabJikNode_set(init_vals, field_name, expr);
         if (jik_parser_current_token(p)->type != TOK_RCURL) {

test/jik/test_compile_fail_semantic.jik

@@ -487,6 +487,50 @@ end
     )
 end
 
+func test_compile_fail_31(ts):
+    utils::assert_compile_fail_source(ts,
+"""
+struct Foo:
+    x: int
+end
+
+func main():
+    y := 1
+    value := Foo{y}
+end
+""",
+        "unknown field name: \"y\"")
+end
+
+func test_compile_fail_32(ts):
+    utils::assert_compile_fail_source(ts,
+"""
+struct Foo:
+    x: int
+end
+
+func main():
+    value := Foo{x}
+end
+""",
+        "undefined symbol: x")
+end
+
+func test_compile_fail_33(ts):
+    utils::assert_compile_fail_source(ts,
+"""
+struct Foo:
+    x: int
+end
+
+func main():
+    x := "wrong"
+    value := Foo{x}
+end
+""",
+        "type mismatch: required int, got String")
+end
+
 func run_tests(ts):
     test_compile_fail_01(ts)
     test_compile_fail_02(ts)
@@ -518,4 +562,7 @@ func run_tests(ts):
     test_compile_fail_28(ts)
     test_compile_fail_29(ts)
     test_compile_fail_30(ts)
+    test_compile_fail_31(ts)
+    test_compile_fail_32(ts)
+    test_compile_fail_33(ts)
 end

test/jik/test_struct_field_init.jik

@@ -0,0 +1,80 @@
+use "jik/testing" as test
+use "support/module_shapes" as shapes
+
+
+struct Settings:
+    host: String
+    port: int
+    verbose: bool
+end
+
+struct Label:
+    text: String
+end
+
+struct Holder:
+    label: Label
+end
+
+
+func test_all_shorthand(ts):
+    host := "localhost"
+    port := 8080
+    verbose := true
+    settings := Settings{host, port, verbose}
+
+    test::suite_assert(ts, settings.host == "localhost", site())
+    test::suite_assert(ts, settings.port == 8080, site())
+    test::suite_assert(ts, settings.verbose, site())
+end
+
+func test_mixed_and_omitted_fields(ts):
+    port := 9000
+    verbose := true
+    settings := Settings{port, host = "example.com", verbose}
+    defaults := Settings{port}
+
+    test::suite_assert(ts, settings.host == "example.com", site())
+    test::suite_assert(ts, settings.port == 9000, site())
+    test::suite_assert(ts, settings.verbose, site())
+    test::suite_assert(ts, defaults.host == "", site())
+    test::suite_assert(ts, defaults.port == 9000, site())
+end
+
+func test_reordered_multiline_shorthand(ts):
+    host := "reordered"
+    port := 1234
+    verbose := false
+    settings := Settings{
+        verbose,
+        host,
+        port
+    }
+
+    test::suite_assert(ts, settings.host == "reordered", site())
+    test::suite_assert(ts, settings.port == 1234, site())
+    test::suite_assert(ts, not settings.verbose, site())
+end
+
+func test_imported_struct_and_composite_field(ts):
+    name := "Ada"
+    tags := ["compiler"]
+    nickname := Some{"analyst"}
+    person := shapes::Person{name, tags, nickname}
+
+    text := "nested"
+    label := Label{text}
+    holder := Holder{label}
+
+    test::suite_assert(ts, person.name == "Ada", site())
+    test::suite_assert(ts, person.tags[0] == "compiler", site())
+    test::suite_assert(ts, person.nickname? == "analyst", site())
+    test::suite_assert(ts, holder.label.text == "nested", site())
+end
+
+func run_tests(ts):
+    test_all_shorthand(ts)
+    test_mixed_and_omitted_fields(ts)
+    test_reordered_multiline_shorthand(ts)
+    test_imported_struct_and_composite_field(ts)
+end

test/jik/tests.jik

@@ -44,6 +44,7 @@ use "test_compile_fail_regions"
 use "test_region_safe_functions"
 use "test_region_ergonomics"
 use "test_compile_fail_modules"
+use "test_struct_field_init"
 
 
 func main():
@@ -93,6 +94,7 @@ func main():
     test_region_safe_functions::run_tests(ts)
     test_region_ergonomics::run_tests(ts)
     test_compile_fail_modules::run_tests(ts)
+    test_struct_field_init::run_tests(ts)
 
     test::suite_finish(ts)