Make into_condition a shorthand for Into::<Condition>::into (#939)

## PR Info

Implemented `IntoCondition` for `T: Into<Cond>`. If you have manually
implemented this trait, it may cause conflicts. You should rewrite it as
`impl From<..> for Condition`.

Author: Huliiiiii

CHANGELOG.md

@@ -251,6 +251,8 @@ from_tbl: "foo".into_table_ref(),
 
 ### Minor breaking changes
 
+* Implemented `IntoCondition` for `T: Into<Cond>`. If you have manually implemented this trait, it may cause conflicts. You should rewrite it as `impl From<..> for Condition`.
+
 * Unboxed `Value` variants may cause compile error. Simply remove the `Box` in these cases https://github.com/SeaQL/sea-query/pull/925
 ```rust
 error[E0308]: mismatched types

src/query/condition.rs

@@ -14,11 +14,39 @@ pub struct Condition {
     pub(crate) conditions: Vec<ConditionExpression>,
 }
 
-pub trait IntoCondition {
-    fn into_condition(self) -> Condition;
+pub type Cond = Condition;
+
+impl From<Expr> for Condition {
+    fn from(expr: Expr) -> Self {
+        Condition {
+            negate: false,
+            condition_type: ConditionType::All,
+            conditions: vec![ConditionExpression::Expr(expr)],
+        }
+    }
 }
 
-pub type Cond = Condition;
+impl From<ConditionExpression> for Condition {
+    fn from(ce: ConditionExpression) -> Self {
+        Condition {
+            negate: false,
+            condition_type: ConditionType::All,
+            conditions: vec![ce],
+        }
+    }
+}
+
+/// A helper trait.
+///
+/// You shouldn't implement this manually.
+pub trait IntoCondition: Into<Condition> {
+    #[inline(always)]
+    fn into_condition(self) -> Condition {
+        self.into()
+    }
+}
+
+impl<T> IntoCondition for T where T: Into<Condition> {}
 
 /// An internal representation of conditions.
 /// May be refactored away in the future if we can get our head around it.
@@ -310,26 +338,6 @@ impl From<Expr> for ConditionExpression {
     }
 }
 
-impl From<Expr> for Condition {
-    fn from(condition: Expr) -> Self {
-        Condition {
-            negate: false,
-            condition_type: ConditionType::All,
-            conditions: vec![ConditionExpression::Expr(condition)],
-        }
-    }
-}
-
-impl From<ConditionExpression> for Condition {
-    fn from(ce: ConditionExpression) -> Self {
-        Condition {
-            negate: false,
-            condition_type: ConditionType::All,
-            conditions: vec![ce],
-        }
-    }
-}
-
 /// Macro to easily create an [`Condition::any`].
 ///
 /// # Examples
@@ -613,18 +621,6 @@ pub trait ConditionalStatement {
         C: IntoCondition;
 }
 
-impl IntoCondition for Expr {
-    fn into_condition(self) -> Condition {
-        Condition::all().add(self)
-    }
-}
-
-impl IntoCondition for Condition {
-    fn into_condition(self) -> Condition {
-        self
-    }
-}
-
 impl ConditionHolder {
     pub fn new() -> Self {
         Self::default()