De Morgan's Law assist now correctly inverts <, <=, >, >=.

crates/ide_assists/src/handlers/apply_demorgan.rs

@@ -11,13 +11,13 @@ use crate::{utils::invert_boolean_expression, AssistContext, AssistId, AssistKin
 //
 // ```
 // fn main() {
-//     if x != 4 ||$0 y < 3 {}
+//     if x != 4 ||$0 y < 3.14 {}
 // }
 // ```
 // ->
 // ```
 // fn main() {
-//     if !(x == 4 && !(y < 3)) {}
+//     if !(x == 4 && !(y < 3.14)) {}
 // }
 // ```
 pub(crate) fn apply_demorgan(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
@@ -32,11 +32,11 @@ pub(crate) fn apply_demorgan(acc: &mut Assists, ctx: &AssistContext) -> Option<(
 
     let lhs = expr.lhs()?;
     let lhs_range = lhs.syntax().text_range();
-    let not_lhs = invert_boolean_expression(lhs);
+    let not_lhs = invert_boolean_expression(&ctx.sema, lhs);
 
     let rhs = expr.rhs()?;
     let rhs_range = rhs.syntax().text_range();
-    let not_rhs = invert_boolean_expression(rhs);
+    let not_rhs = invert_boolean_expression(&ctx.sema, rhs);
 
     acc.add(
         AssistId("apply_demorgan", AssistKind::RefactorRewrite),

crates/ide_assists/src/handlers/early_return.rs

@@ -111,7 +111,7 @@ pub(crate) fn convert_to_guarded_return(acc: &mut Assists, ctx: &AssistContext)
                     let new_expr = {
                         let then_branch =
                             make::block_expr(once(make::expr_stmt(early_expression).into()), None);
-                        let cond = invert_boolean_expression(cond_expr);
+                        let cond = invert_boolean_expression(&ctx.sema, cond_expr);
                         make::expr_if(make::condition(cond, None), then_branch, None)
                             .indent(if_indent_level)
                     };

crates/ide_assists/src/handlers/invert_if.rs

@@ -50,7 +50,7 @@ pub(crate) fn invert_if(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     };
 
     acc.add(AssistId("invert_if", AssistKind::RefactorRewrite), "Invert if", if_range, |edit| {
-        let flip_cond = invert_boolean_expression(cond.clone());
+        let flip_cond = invert_boolean_expression(&ctx.sema, cond.clone());
         edit.replace_ast(cond, flip_cond);
 
         let else_node = else_block.syntax();

crates/ide_assists/src/tests/generated.rs

@@ -147,12 +147,12 @@ fn doctest_apply_demorgan() {
         "apply_demorgan",
         r#####"
 fn main() {
-    if x != 4 ||$0 y < 3 {}
+    if x != 4 ||$0 y < 3.14 {}
 }
 "#####,
         r#####"
 fn main() {
-    if !(x == 4 && !(y < 3)) {}
+    if !(x == 4 && !(y < 3.14)) {}
 }
 "#####,
     )

crates/ide_assists/src/utils.rs

@@ -3,8 +3,11 @@
 use std::ops;
 
 use ast::TypeBoundsOwner;
-use hir::{Adt, HasSource};
+use hir::{Adt, HasSource, Semantics};
-use ide_db::{helpers::SnippetCap, RootDatabase};
+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 {
+pub(crate) fn invert_boolean_expression(
-    if let Some(expr) = invert_special_case(&expr) {
+    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()
 }

crates/ide_db/src/helpers.rs

@@ -45,6 +45,10 @@ impl FamousDefs<'_, '_> {
         self.find_crate("core")
     }
 
+    pub fn core_cmp_Ord(&self) -> Option<Trait> {
+        self.find_trait("core:cmp:Ord")
+    }
+
     pub fn core_convert_From(&self) -> Option<Trait> {
         self.find_trait("core:convert:From")
     }

crates/ide_db/src/helpers/famous_defs_fixture.rs

@@ -1,5 +1,15 @@
 //- /libcore.rs crate:core
 //! Signatures of traits, types and functions from the core lib for use in tests.
+pub mod cmp {
+
+    pub trait Ord {
+        fn cmp(&self, other: &Self) -> Ordering;
+        fn max(self, other: Self) -> Self;
+        fn min(self, other: Self) -> Self;
+        fn clamp(self, min: Self, max: Self) -> Self;
+    }
+}
+
 pub mod convert {
     pub trait From<T> {
         fn from(t: T) -> Self;
@@ -109,6 +119,7 @@ pub mod option {
 
 pub mod prelude {
     pub use crate::{
+        cmp::Ord,
         convert::From,
         default::Default,
         iter::{IntoIterator, Iterator},