From 9db970ee082e315cfa04db163fe2e0268b618531 Mon Sep 17 00:00:00 2001
From: lbrande <lovbra00@gmail.com>
Date: Mon, 22 Feb 2021 16:23:42 +0100
Subject: De Morgan's Law assist now correctly inverts <, <=, >, >=.

---
 crates/ide_assists/src/utils.rs | 50 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

(limited to 'crates/ide_assists/src/utils.rs')

diff --git a/crates/ide_assists/src/utils.rs b/crates/ide_assists/src/utils.rs
index cd026d432..38ed74673 100644
--- a/crates/ide_assists/src/utils.rs
+++ b/crates/ide_assists/src/utils.rs
@@ -3,8 +3,11 @@
 use std::ops;
 
 use ast::TypeBoundsOwner;
-use hir::{Adt, HasSource};
-use ide_db::{helpers::SnippetCap, RootDatabase};
+use hir::{Adt, HasSource, Semantics};
+use ide_db::{
+    helpers::{FamousDefs, SnippetCap},
+    RootDatabase,
+};
 use itertools::Itertools;
 use stdx::format_to;
 use syntax::{
@@ -205,18 +208,34 @@ pub(crate) fn vis_offset(node: &SyntaxNode) -> TextSize {
         .unwrap_or_else(|| node.text_range().start())
 }
 
-pub(crate) fn invert_boolean_expression(expr: ast::Expr) -> ast::Expr {
-    if let Some(expr) = invert_special_case(&expr) {
+pub(crate) fn invert_boolean_expression(
+    sema: &Semantics<RootDatabase>,
+    expr: ast::Expr,
+) -> ast::Expr {
+    if let Some(expr) = invert_special_case(sema, &expr) {
         return expr;
     }
     make::expr_prefix(T![!], expr)
 }
 
-fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
+fn invert_special_case(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> Option<ast::Expr> {
     match expr {
         ast::Expr::BinExpr(bin) => match bin.op_kind()? {
             ast::BinOp::NegatedEqualityTest => bin.replace_op(T![==]).map(|it| it.into()),
             ast::BinOp::EqualityTest => bin.replace_op(T![!=]).map(|it| it.into()),
+            // Swap `<` with `>=`, `<=` with `>`, ... if operands `impl Ord`
+            ast::BinOp::LesserTest if bin_impls_ord(sema, bin) => {
+                bin.replace_op(T![>=]).map(|it| it.into())
+            }
+            ast::BinOp::LesserEqualTest if bin_impls_ord(sema, bin) => {
+                bin.replace_op(T![>]).map(|it| it.into())
+            }
+            ast::BinOp::GreaterTest if bin_impls_ord(sema, bin) => {
+                bin.replace_op(T![<=]).map(|it| it.into())
+            }
+            ast::BinOp::GreaterEqualTest if bin_impls_ord(sema, bin) => {
+                bin.replace_op(T![<]).map(|it| it.into())
+            }
             // Parenthesize other expressions before prefixing `!`
             _ => Some(make::expr_prefix(T![!], make::expr_paren(expr.clone()))),
         },
@@ -247,6 +266,27 @@ fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
     }
 }
 
+fn bin_impls_ord(sema: &Semantics<RootDatabase>, bin: &ast::BinExpr) -> bool {
+    if let (Some(lhs), Some(rhs)) = (bin.lhs(), bin.rhs()) {
+        return sema.type_of_expr(&lhs) == sema.type_of_expr(&rhs)
+            && impls_ord(sema, &lhs)
+            && impls_ord(sema, &rhs);
+    }
+    false
+}
+
+fn impls_ord(sema: &Semantics<RootDatabase>, expr: &ast::Expr) -> bool {
+    let krate = sema.scope(expr.syntax()).module().map(|it| it.krate());
+    let famous_defs = FamousDefs(&sema, krate);
+
+    if let Some(ty) = sema.type_of_expr(expr) {
+        if let Some(ord_trait) = famous_defs.core_cmp_Ord() {
+            return ty.autoderef(sema.db).any(|ty| ty.impls_trait(sema.db, ord_trait, &[]));
+        }
+    }
+    false
+}
+
 pub(crate) fn next_prev() -> impl Iterator<Item = Direction> {
     [Direction::Next, Direction::Prev].iter().copied()
 }
-- 
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