From c500044baeb381392433a0fc9410ef5a483db7cc Mon Sep 17 00:00:00 2001
From: Henrixounez <30901439+Henrixounez@users.noreply.github.com>
Date: Wed, 29 Apr 2020 12:31:18 +0200
Subject: [PATCH] checker: unreachable code warning

---
 vlib/v/ast/ast.v                          | 76 +++++++++++++++++++++++
 vlib/v/checker/checker.v                  | 12 ++++
 vlib/v/checker/tests/unreachable_code.out |  7 +++
 vlib/v/checker/tests/unreachable_code.vv  |  8 +++
 4 files changed, 103 insertions(+)
 create mode 100644 vlib/v/checker/tests/unreachable_code.out
 create mode 100644 vlib/v/checker/tests/unreachable_code.vv

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index cd15891035..bdc434ac24 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -852,3 +852,79 @@ fn (expr Expr) position() token.Position {
 		}
 	}
 }
+
+fn (stmt Stmt) position() token.Position {
+	match mut stmt {
+		AssertStmt {
+			return it.pos
+		}
+		AssignStmt {
+			return it.pos
+		}
+		// Attr {
+		// }
+		// Block {
+		// }
+		// BranchStmt {
+		// }
+		Comment {
+			return it.pos
+		}
+		CompIf {
+			return it.pos
+		}
+		ConstDecl {
+			return it.pos
+		}
+		// DeferStmt {
+		// }
+		EnumDecl {
+			return it.pos
+		}
+		ExprStmt {
+			return it.pos
+		}
+		FnDecl {
+			return it.pos
+		}
+		ForCStmt {
+			return it.pos
+		}
+		ForInStmt {
+			return it.pos
+		}
+		ForStmt {
+			return it.pos
+		}
+		// GlobalDecl {
+		// }
+		// GoStmt {
+		// }
+		// GotoLabel {
+		// }
+		// GotoStmt {
+		// }
+		// HashStmt {
+		// }
+		Import {
+			return it.pos
+		}
+		// InterfaceDecl {
+		// }
+		// Module {
+		// }
+		Return {
+			return it.pos
+		}
+		StructDecl {
+			return it.pos
+		}
+		// TypeDecl {
+		// }
+		// UnsafeStmt {
+		// }
+		else {
+			return token.Position{}
+		}
+	}
+}
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index d87181a60f..839db6917f 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -34,6 +34,7 @@ mut:
 	// checked_ident  string // to avoid infinit checker loops
 	var_decl_name  string
 	returns        bool
+	scope_returns  bool
 	mod            string // current module name
 	is_builtin_mod bool // are we in `builtin`?
 }
@@ -1398,6 +1399,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 		ast.Return {
 			c.returns = true
 			c.return_stmt(mut it)
+			c.scope_returns = true
 		}
 		ast.StructDecl {
 			c.struct_decl(it)
@@ -1416,10 +1418,20 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 }
 
 fn (mut c Checker) stmts(stmts []ast.Stmt) {
+	mut unreachable := token.Position{line_nr: -1}
 	c.expected_type = table.void_type
 	for stmt in stmts {
+		if c.scope_returns {
+			if unreachable.line_nr == -1 {
+				unreachable = stmt.position()
+			}
+		}
 		c.stmt(stmt)
 	}
+	if unreachable.line_nr >= 0 {
+		c.warn('unreachable code', unreachable)
+	}
+	c.scope_returns = false
 	c.expected_type = table.void_type
 }
 
diff --git a/vlib/v/checker/tests/unreachable_code.out b/vlib/v/checker/tests/unreachable_code.out
new file mode 100644
index 0000000000..b78ee492d9
--- /dev/null
+++ b/vlib/v/checker/tests/unreachable_code.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/unreachable_code.v:3:7: error: unreachable code 
+    1| fn foo() int {
+    2|     return if 1 == 1 { 1 } else { 2 }
+    3|     a := 1
+                ^
+    4|     println(a)
+    5| }
diff --git a/vlib/v/checker/tests/unreachable_code.vv b/vlib/v/checker/tests/unreachable_code.vv
new file mode 100644
index 0000000000..7da480f8aa
--- /dev/null
+++ b/vlib/v/checker/tests/unreachable_code.vv
@@ -0,0 +1,8 @@
+fn foo() int {
+	return if 1 == 1 { 1 } else { 2 }
+	a := 1
+	println(a)
+}
+fn main() {
+	foo()
+}