From 237d83b2eecc40441ac247c17ec19f4c9ce603f8 Mon Sep 17 00:00:00 2001
From: Joe Conigliaro <joe.conigliaro@gmail.com>
Date: Thu, 27 Feb 2020 21:12:30 +1100
Subject: [PATCH] v2: more work on AssignStmt & multi ret & initial blank ident

---
 vlib/v/ast/ast.v         |  1 +
 vlib/v/ast/scope.v       |  7 +++++++
 vlib/v/checker/checker.v | 27 ++++++++++++++++++++-------
 vlib/v/parser/parser.v   | 18 ++++++++++++++++++
 4 files changed, 46 insertions(+), 7 deletions(-)

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 6511c4fc8c..1e20f9d8e3 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -388,6 +388,7 @@ pub:
 	left  []Ident
 	right []Expr
 	op    token.Kind
+	pos   token.Position
 }
 
 // e.g. `[unsafe_fn]`
diff --git a/vlib/v/ast/scope.v b/vlib/v/ast/scope.v
index 5be3cd1af8..36d1e58844 100644
--- a/vlib/v/ast/scope.v
+++ b/vlib/v/ast/scope.v
@@ -44,6 +44,13 @@ pub fn (s &Scope) find_var(name string) ?VarDecl {
 	return none
 }
 
+pub fn (s &Scope) known_var(name string) bool {
+	if _ := s.find_var(name) {
+		return true
+	}
+	return false
+}
+
 pub fn (s mut Scope) register_var(var VarDecl) {
 	if x := s.find_var(var.name) {
 		// println('existing var: $var.name')
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 568b806203..771fc8342e 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -283,11 +283,28 @@ pub fn (c mut Checker) return_stmt(return_stmt ast.Return) {
 	}
 }
 
-/*
 pub fn (c mut Checker) assign_stmt(assign_stmt ast.AssignStmt) {
+    // multi return
+    if assign_stmt.left.len > assign_stmt.right.len {
+        right := c.expr(assign_stmt.right[0])
+        right_sym := c.table.get_type_symbol(right)
+        info := right_sym.mr_info()
+        if right_sym.kind != .multi_return {
+            c.error('wrong number of vars', assign_stmt.pos)
+        }
+        mut scope := c.file.scope.innermost(assign_stmt.pos.pos) or {
+            c.file.scope
+        }
+        for i, ident in assign_stmt.left {
+			// TODO: check types
+			scope.override_var(ast.VarDecl{
+                name: ident.name
+                typ: info.types[i]
+            })
+        }
+    }
+	// TODO: multiple assign
 }
-*/
-
 
 pub fn (c mut Checker) array_init(array_init mut ast.ArrayInit) table.Type {
 	mut elem_type := table.void_type
@@ -330,12 +347,9 @@ fn (c mut Checker) stmt(node ast.Stmt) {
 		ast.Return {
 			c.return_stmt(it)
 		}
-		/*
 		ast.AssignStmt {
 			c.assign_stmt(it)
 		}
-		*/
-
 		ast.ConstDecl {
 			for i, expr in it.exprs {
 				mut field := it.fields[i]
@@ -480,7 +494,6 @@ pub fn (c mut Checker) ident(ident mut ast.Ident) table.Type {
 		mut found := true
 		mut var_scope := &ast.Scope(0)
 		mut var := ast.VarDecl{}
-		// mut var_scope, mut var := start_scope.find_scope_and_var(ident.name) or {
 		var_scope,var = start_scope.find_scope_and_var(ident.name) or {
 			found = false
 			c.error('not found: $ident.name - POS: $ident.pos.pos', ident.pos)
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index ded6ad3b6f..281e6b1128 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -458,6 +458,12 @@ pub fn (p mut Parser) parse_ident(is_c bool) ast.Ident {
 	// p.warn('name ')
 	// left := p.parse_ident()
 	name := p.check_name()
+	if name == '_' {
+		return ast.Ident{
+			kind: .blank_ident
+			pos: p.tok.position()
+		}
+	}
 	mut ident := ast.Ident{
 		name: name
 		is_c: is_c
@@ -1519,10 +1525,22 @@ pub fn (p mut Parser) assign_stmt() ast.AssignStmt {
 	op := p.tok.kind
 	p.next() // :=, =
 	expr,_ := p.expr(0)
+	is_decl := op == .decl_assign
+	for ident in idents {
+		if is_decl && ident.kind == .blank_ident {
+			if p.scope.known_var(ident.name) {
+				p.error('redefinition of `$ident.name`')
+			}
+			p.scope.register_var(ast.VarDecl{
+				name: ident.name
+			})
+		}
+	}
 	return ast.AssignStmt{
 		left: idents
 		right: [expr]
 		op: op
+		pos: p.tok.position()
 	}
 }