From 7ea9706c94d054d5ba45585bc9775f65010ca159 Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Tue, 2 Mar 2021 11:43:47 -0700
Subject: [PATCH] warn when overwriting a predicate (#848)

---
 src/machine/compile.rs    | 24 +++++++++++++++++++++++-
 src/machine/load_state.rs |  2 --
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/machine/compile.rs b/src/machine/compile.rs
index bfea3f2f..eea744a2 100644
--- a/src/machine/compile.rs
+++ b/src/machine/compile.rs
@@ -1293,6 +1293,26 @@ fn mergeable_indexed_subsequences(
     false
 }
 
+fn print_overwrite_warning(
+    compilation_target: &CompilationTarget,
+    code_ptr: IndexPtr,
+    key: &PredicateKey,
+) {
+    if let CompilationTarget::Module(ref module_name) = compilation_target {
+        match module_name.as_str() {
+            "builtins" | "loader" => return,
+            _ => {}
+        }
+    }
+
+    match code_ptr {
+        IndexPtr::DynamicUndefined | IndexPtr::Undefined => return,
+        _ => {}
+    }
+
+    println!("Warning: overwriting {}/{}", key.0, key.1);
+}
+
 impl<'a> LoadState<'a> {
     fn compile_standalone_clause(
         &mut self,
@@ -1403,7 +1423,7 @@ impl<'a> LoadState<'a> {
                         predicates.compilation_target.clone(),
                     );
                 }
-            }
+            };
 
             match self
                 .wam
@@ -1440,6 +1460,8 @@ impl<'a> LoadState<'a> {
             }
         }
 
+        print_overwrite_warning(&predicates.compilation_target, code_index.get(), &key);
+
         set_code_index(
             &mut self.retraction_info,
             &predicates.compilation_target,
diff --git a/src/machine/load_state.rs b/src/machine/load_state.rs
index b2567725..96f88d04 100644
--- a/src/machine/load_state.rs
+++ b/src/machine/load_state.rs
@@ -35,7 +35,6 @@ pub(super) fn set_code_index(
                 code_index.set(code_ptr);
                 RetractionRecord::AddedUserPredicate(key)
             } else {
-                // TODO: emit warning about overwriting previous record
                 let replaced = code_index.replace(code_ptr);
                 RetractionRecord::ReplacedUserPredicate(key, replaced)
             }
@@ -45,7 +44,6 @@ pub(super) fn set_code_index(
                 code_index.set(code_ptr);
                 RetractionRecord::AddedModulePredicate(module_name.clone(), key)
             } else {
-                // TODO: emit warning about overwriting previous record
                 let replaced = code_index.replace(code_ptr);
                 RetractionRecord::ReplacedModulePredicate(module_name.clone(), key, replaced)
             }
-- 
2.54.0