Address review comments

diesel/src/mysql/connection/stmt/iterator.rs

@@ -67,14 +67,20 @@ impl<'a> Row<Mysql> for MysqlRow<'a> {
         self.binds.len()
     }
 
-    fn column_name(&self) -> &str {
+    fn column_name(&self) -> Option<&str> {
         let metadata = self.stmt.metadata().expect("Failed to get metadata");
         let field = if self.col_idx == 0 {
             metadata.fields()[0]
         } else {
             metadata.fields()[self.col_idx - 1]
         };
-        unsafe { CStr::from_ptr(field.name).to_str().expect("It's utf8") }
+        unsafe {
+            Some(CStr::from_ptr(field.name).to_str().expect(
+                "Diesel assumes that your mysql database uses the \
+                 utf8mb4 encoding. That's not the case if you hit \
+                 this error message.",
+            ))
+        }
     }
 }
 

diesel/src/pg/connection/row.rs

@@ -40,8 +40,8 @@ impl<'a> Row<Pg> for PgRow<'a> {
         self.db_result.column_count()
     }
 
-    fn column_name(&self) -> &str {
-        self.db_result.column_name(self.col_idx)
+    fn column_name(&self) -> Option<&str> {
+        Some(self.db_result.column_name(self.col_idx))
     }
 }
 

diesel/src/row.rs

@@ -32,7 +32,7 @@ pub trait Row<DB: Backend> {
     fn column_count(&self) -> usize;
 
     /// Name of the current column
-    fn column_name(&self) -> &str;
+    fn column_name(&self) -> Option<&str>;
 }
 
 /// Represents a row of a SQL query, where the values are accessed by name

diesel/src/sqlite/connection/functions.rs

@@ -75,7 +75,7 @@ impl<'a> Row<Sqlite> for FunctionRow<'a> {
         self.args.len()
     }
 
-    fn column_name(&self) -> &str {
-        unimplemented!()
+    fn column_name(&self) -> Option<&str> {
+        None
     }
 }

diesel/src/sqlite/connection/sqlite_value.rs

@@ -104,16 +104,22 @@ impl Row<Sqlite> for SqliteRow {
         })
     }
 
-    fn column_name(&self) -> &str {
+    fn column_name(&self) -> Option<&str> {
         unsafe {
             let ptr = if self.next_col_index == 0 {
                 ffi::sqlite3_column_name(self.stmt.as_ptr(), 0)
             } else {
                 ffi::sqlite3_column_name(self.stmt.as_ptr(), self.next_col_index - 1)
             };
-            std::ffi::CStr::from_ptr(ptr)
-                .to_str()
-                .expect("Sqlite3 doc's say it's UTF8")
+            Some(
+                std::ffi::CStr::from_ptr(ptr)
+                    .to_str()
+                    .expect(
+                        "The Sqlite documentation states that this is UTF8. \
+                         If you see this error message something has gone \
+                         horribliy wrong. Please open an issue at the \
+                         diesel repository."),
+            )
         }
     }