Types and completion in VS Code

Contents · Setup · Extension installation and settings

Install Nagi extension 0.1.9 and the latest nagic, then open the Nagi repository in VS Code. This walkthrough uses working code to try type hovers, field completion, and definition navigation. Both High and Low are supported.

Indentation support

Extension 0.1.9 supports indentation after headers such as def main():, else/case alignment, and closing delimiter alignment in multiline expressions.

Typing the final colon of else: or case ...: aligns it with its enclosing if or match. The default is four spaces; the editor's indentation settings are respected. This runs without the compiler, including in new untitled files. See indentation while typing for behavior and settings.

Open the example

Open examples/tutorial/editor_types.nagi, which contains this complete program:

class Count:
    value: i64

def parse_count(text: str) -> Result[Count, Error]:
    number = try parse_i64(text)
    return ok(Count(value=number))

def show(count: Count):
    print(count.value)

def main():
    result = parse_count("42")
    match result:
        case Ok(count):
            show(count)
        case Err(problem):
            print(error_message(problem))

Use the top-right run button or Nagi: 実行 (Run) in the Command Palette to print 42. Execution saves the file first. Extension command labels are currently Japanese.

Inspect variable types

Hover these names. The compiler's inferred types appear even without explicit annotations.

Case names exist only in that case. Typing count after the match does not show the Ok binding's type. New variables inside if/while/for/scope blocks also stop being available outside the block. Unannotated integers normally infer i64 and floats f64. See types and inference.

Complete fields

In show's print(count.value), remove value to get print(count.). If candidates do not appear, press Ctrl+Space. Selecting value: i64 restores count.value. You can also complete after typing count.va.

Calls returning classes (make().), nested fields (container.item.), and Copy-class list elements (items[0].) offer fields for the expression's type. Selecting a field inserts only its name.

Result has type Result[Count, Error], so result. does not offer Count fields. Extract Count through match as above. In a Result-returning function, use count = try parse_count("42") or (try parse_count("42")).value. Fields on awaited values similarly use (await fetch()).field.

Call functions and find definitions

Type part of a name or press Ctrl+Space for project functions, classes, and built-ins. Function completion inserts argument placeholders; Tab moves between them. Class completion inserts named arguments such as Count(value=...). Typing ( or , shows parameter order and types.

Press F12 on parse_count or Count to reach its definition. On an import string, F12 opens the file. Previously saved files support unsaved edits and changes in open imports.

Try F12 on these local names:

Reassigned names navigate to their first binding. A for binding reusing an outer name targets the loop binding inside the loop and the original afterward. New if/while/scope/case bindings apply only in their blocks. Navigation can work after moves or initializer type errors if a binding is identifiable. F12 for class field names and built-ins is not supported.

When editor information is unavailable

Previously saved Nagi/Low files are analyzed in memory with their unsaved edits, including open imports and native Low. Queries do not save or build sources. Save new files and nagi.toml to use project information.

Extension 0.1.9 also offers keyword/type completion and built-in completion, hover, and argument hints in new unsaved files, without a compiler, and in untrusted workspaces. When the source cannot be analyzed, unresolved imports or same-name bindings in the file suppress built-in information that could refer to another definition. Local types, field candidates, and F12 require the compiler and a trusted workspace.

Unsaved edits clear old Problems diagnostics. Save or run Nagi: 型検査 (Type Check) to update them. Seeing a type in a hover or completion does not mean the whole program passed checking.