Add Decodal formatter

doc/manual/souce/components.md

@@ -8,7 +8,7 @@ The public surface is intentionally organized by use case: execute Decodal with
 ### Rust crate
 
 The `decodal` crate is the primary Rust runtime and embedding API.
-It owns parsing, evaluation, materialization, diagnostics, host-provided values, and schema/decode traits.
+It owns parsing, formatting, evaluation, materialization, diagnostics, host-provided values, and schema/decode traits.
 Rust applications should use this crate when they want to load Decodal source, evaluate it, or embed Decodal into a host program.
 
 Important paths:

doc/manual/souce/formatting.md

@@ -0,0 +1,50 @@
+# Formatting
+
+Decodal includes an initial source formatter for parsed Decodal code.
+The formatter is available from the Rust crate, the CLI, the WebAssembly package, and the playground.
+
+## CLI
+
+Print formatted source to stdout:
+
+```sh
+decodal fmt config.dcdl
+```
+
+Format in place:
+
+```sh
+decodal fmt --write config.dcdl
+```
+
+Read from stdin:
+
+```sh
+cat config.dcdl | decodal fmt -
+```
+
+## Rust
+
+```rust
+let formatted = decodal::format_source("Server={port=Int default 8080;};")?;
+```
+
+## WebAssembly
+
+```js
+import init, { formatSource } from 'decodal-wasm';
+
+await init();
+const result = JSON.parse(formatSource('Server={port=Int default 8080;};'));
+
+if (result.ok) {
+  console.log(result.source);
+} else {
+  console.error(result.error);
+}
+```
+
+## Current limitation
+
+The formatter currently rejects source containing line comments rather than silently dropping them.
+Comment-preserving formatting requires attaching comments to syntax nodes or formatting from a concrete syntax tree, and should be implemented before comment-heavy source is formatted automatically.

doc/manual/souce/index.md

@@ -7,7 +7,8 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
 
 1. [Introduction](./introduction.md)
 2. [Components](./components.md)
-3. [Language Specification](./language/index.md)
+3. [Formatting](./formatting.md)
+4. [Language Specification](./language/index.md)
    1. [Lexical Structure and Syntax](./language/syntax.md)
    2. [Value](./language/value/index.md)
       1. [String](./language/value/string.md)
@@ -36,7 +37,7 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
    9. [Materialization and Errors](./language/materialization-and-errors.md)
    10. [Naming Conventions](./language/naming.md)
    11. [Examples](./language/examples.md)
-4. [Implementation Design](./design/index.md)
+5. [Implementation Design](./design/index.md)
    1. [Execution Pipeline](./design/execution-pipeline.md)
    2. [Runtime Model](./design/runtime-model.md)
    3. [Thunk and Lazy Evaluation](./design/thunk-and-lazy-evaluation.md)
@@ -44,5 +45,5 @@ Decodal は Deferred Constraint Data Language、略称 DCDL のプロジェク
    5. [Diagnostics and Fallback](./design/diagnostics-and-fallback.md)
    6. [Embedding API](./design/embedding-api.md)
    7. [Features](./design/features.md)
-5. [Development](./development.md)
-6. [Open Issues](./open-issues.md)
+6. [Development](./development.md)
+7. [Open Issues](./open-issues.md)