From b86dd1befcba1bbdeb3eef8d556941f22613f7d6 Mon Sep 17 00:00:00 2001
From: Roman Bataev <roman@bataev.me>
Date: Tue, 13 Mar 2018 21:01:06 -0700
Subject: [PATCH] Warn on duplicate defs

---
 core/ns.go                            |  3 +++
 tests/linter/duplicate-def/input.clj  | 11 +++++++++++
 tests/linter/duplicate-def/output.txt |  2 ++
 3 files changed, 16 insertions(+)
 create mode 100644 tests/linter/duplicate-def/input.clj
 create mode 100644 tests/linter/duplicate-def/output.txt

diff --git a/core/ns.go b/core/ns.go
index 79c9e8ed7..d916b2676 100644
--- a/core/ns.go
+++ b/core/ns.go
@@ -107,6 +107,9 @@ func (ns *Namespace) Intern(sym Symbol) *Var {
 		panic(RT.NewErrorWithPos(fmt.Sprintf("WARNING: %s already refers to: %s in namespace %s",
 			sym.ToString(false), existingVar.ToString(false), ns.ToString(false)), sym.GetInfo().Pos()))
 	}
+	if LINTER_MODE && existingVar.expr != nil && !existingVar.ns.Name.Equals(SYMBOLS.joker_core) {
+		printParseWarning(sym.GetInfo().Pos(), "Duplicate def of "+existingVar.ToString(false))
+	}
 	return existingVar
 }
 
diff --git a/tests/linter/duplicate-def/input.clj b/tests/linter/duplicate-def/input.clj
new file mode 100644
index 000000000..344a838f4
--- /dev/null
+++ b/tests/linter/duplicate-def/input.clj
@@ -0,0 +1,11 @@
+(def b)
+(def b 1)
+
+(declare f)
+(defn f [])
+
+(def a 1)
+(def a 2)
+
+(defn f1 [])
+(defn f1 [a])
diff --git a/tests/linter/duplicate-def/output.txt b/tests/linter/duplicate-def/output.txt
new file mode 100644
index 000000000..68876a912
--- /dev/null
+++ b/tests/linter/duplicate-def/output.txt
@@ -0,0 +1,2 @@
+tests/linter/duplicate-def/input.clj:8:6: Parse warning: Duplicate def of #'user/a
+tests/linter/duplicate-def/input.clj:11:7: Parse warning: Duplicate def of #'user/f1