ast: add wrapper structs (AssignStmt/ReturnStmt/IfStmt, BinaryExpr/CallExpr) with TryFrom/From for non-breaking gradual refactors

src/ast.rs

@@ -11,6 +11,8 @@ use std::fmt;
 mod span;
 pub use span::Span;
 mod utils;
+mod nodes;
+pub use nodes::*;
 
 // Span は src/ast/span.rs へ分離（re-export で後方互換維持）
 

src/ast/nodes.rs

@@ -0,0 +1,134 @@
+//! Lightweight wrapper structs around ASTNode variants (non-breaking).
+//!
+//! Purpose: provide a gentle path to work with structured nodes via
+//! TryFrom/From without changing the canonical AST enum. This enables
+//! gradual refactors in builders by converting once at the boundary and
+//! then matching on small, typed wrappers.
+
+use super::{ASTNode, Span};
+
+// ----------------
+// Statements
+// ----------------
+
+#[derive(Debug, Clone)]
+pub struct AssignStmt {
+    pub target: Box<ASTNode>,
+    pub value: Box<ASTNode>,
+    pub span: Span,
+}
+
+impl TryFrom<ASTNode> for AssignStmt {
+    type Error = ASTNode;
+    fn try_from(node: ASTNode) -> Result<Self, Self::Error> {
+        match node {
+            ASTNode::Assignment { target, value, span } => Ok(AssignStmt { target, value, span }),
+            other => Err(other),
+        }
+    }
+}
+
+impl From<AssignStmt> for ASTNode {
+    fn from(s: AssignStmt) -> Self {
+        ASTNode::Assignment { target: s.target, value: s.value, span: s.span }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct ReturnStmt {
+    pub value: Option<Box<ASTNode>>,
+    pub span: Span,
+}
+
+impl TryFrom<ASTNode> for ReturnStmt {
+    type Error = ASTNode;
+    fn try_from(node: ASTNode) -> Result<Self, Self::Error> {
+        match node {
+            ASTNode::Return { value, span } => Ok(ReturnStmt { value, span }),
+            other => Err(other),
+        }
+    }
+}
+
+impl From<ReturnStmt> for ASTNode {
+    fn from(s: ReturnStmt) -> Self {
+        ASTNode::Return { value: s.value, span: s.span }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct IfStmt {
+    pub condition: Box<ASTNode>,
+    pub then_body: Vec<ASTNode>,
+    pub else_body: Option<Vec<ASTNode>>,
+    pub span: Span,
+}
+
+impl TryFrom<ASTNode> for IfStmt {
+    type Error = ASTNode;
+    fn try_from(node: ASTNode) -> Result<Self, Self::Error> {
+        match node {
+            ASTNode::If { condition, then_body, else_body, span } => Ok(IfStmt { condition, then_body, else_body, span }),
+            other => Err(other),
+        }
+    }
+}
+
+impl From<IfStmt> for ASTNode {
+    fn from(s: IfStmt) -> Self {
+        ASTNode::If { condition: s.condition, then_body: s.then_body, else_body: s.else_body, span: s.span }
+    }
+}
+
+// ----------------
+// Expressions
+// ----------------
+
+#[derive(Debug, Clone)]
+pub struct BinaryExpr {
+    pub operator: super::BinaryOperator,
+    pub left: Box<ASTNode>,
+    pub right: Box<ASTNode>,
+    pub span: Span,
+}
+
+impl TryFrom<ASTNode> for BinaryExpr {
+    type Error = ASTNode;
+    fn try_from(node: ASTNode) -> Result<Self, Self::Error> {
+        match node {
+            ASTNode::BinaryOp { operator, left, right, span } =>
+                Ok(BinaryExpr { operator, left, right, span }),
+            other => Err(other),
+        }
+    }
+}
+
+impl From<BinaryExpr> for ASTNode {
+    fn from(e: BinaryExpr) -> Self {
+        ASTNode::BinaryOp { operator: e.operator, left: e.left, right: e.right, span: e.span }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct CallExpr {
+    pub name: String,
+    pub arguments: Vec<ASTNode>,
+    pub span: Span,
+}
+
+impl TryFrom<ASTNode> for CallExpr {
+    type Error = ASTNode;
+    fn try_from(node: ASTNode) -> Result<Self, Self::Error> {
+        match node {
+            ASTNode::FunctionCall { name, arguments, span } => Ok(CallExpr { name, arguments, span }),
+            other => Err(other),
+        }
+    }
+}
+
+impl From<CallExpr> for ASTNode {
+    fn from(c: CallExpr) -> Self {
+        ASTNode::FunctionCall { name: c.name, arguments: c.arguments, span: c.span }
+    }
+}
+