Add inlay hint for exclusive ranges

Adds an inlay hint containing a '<' character to exclusive range expressions and patterns that specify an upper bound.

crates/ide/src/inlay_hints/range_exclusive.rs

@@ -0,0 +1,121 @@
+//! Implementation of "range exclusive" inlay hints:
+//! ```no_run
+//! for i in 0../* < */10 {}
+//! if let ../* < */100 = 50 {}
+//! ```
+use syntax::{ast, SyntaxToken, T};
+
+use crate::{InlayHint, InlayHintsConfig};
+
+pub(super) fn hints(
+    acc: &mut Vec<InlayHint>,
+    config: &InlayHintsConfig,
+    range: impl ast::RangeItem,
+) -> Option<()> {
+    (config.range_exclusive_hints && range.end().is_some())
+        .then(|| {
+            range.op_token().filter(|token| token.kind() == T![..]).map(|token| {
+                acc.push(inlay_hint(token));
+            })
+        })
+        .flatten()
+}
+
+fn inlay_hint(token: SyntaxToken) -> InlayHint {
+    InlayHint {
+        range: token.text_range(),
+        position: crate::InlayHintPosition::After,
+        pad_left: false,
+        pad_right: false,
+        kind: crate::InlayKind::RangeExclusive,
+        label: crate::InlayHintLabel::from("<"),
+        text_edit: None,
+        needs_resolve: false,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        inlay_hints::tests::{check_with_config, DISABLED_CONFIG},
+        InlayHintsConfig,
+    };
+
+    #[test]
+    fn range_exclusive_expression_bounded_above_hints() {
+        check_with_config(
+            InlayHintsConfig { range_exclusive_hints: true, ..DISABLED_CONFIG },
+            r#"
+fn main() {
+    let a = 0..10;
+           //^^<
+    let b = ..100;
+          //^^<
+    let c = (2 - 1)..(7 * 8)
+                 //^^<
+}"#,
+        );
+    }
+
+    #[test]
+    fn range_exclusive_expression_unbounded_above_no_hints() {
+        check_with_config(
+            InlayHintsConfig { range_exclusive_hints: true, ..DISABLED_CONFIG },
+            r#"
+fn main() {
+    let a = 0..;
+    let b = ..;
+}"#,
+        );
+    }
+
+    #[test]
+    fn range_inclusive_expression_no_hints() {
+        check_with_config(
+            InlayHintsConfig { range_exclusive_hints: true, ..DISABLED_CONFIG },
+            r#"
+fn main() {
+    let a = 0..=10;
+    let b = ..=100;
+}"#,
+        );
+    }
+
+    #[test]
+    fn range_exclusive_pattern_bounded_above_hints() {
+        check_with_config(
+            InlayHintsConfig { range_exclusive_hints: true, ..DISABLED_CONFIG },
+            r#"
+fn main() {
+    if let 0..10 = 0 {}
+          //^^<
+    if let ..100 = 0 {}
+         //^^<
+}"#,
+        );
+    }
+
+    #[test]
+    fn range_exclusive_pattern_unbounded_above_no_hints() {
+        check_with_config(
+            InlayHintsConfig { range_exclusive_hints: true, ..DISABLED_CONFIG },
+            r#"
+fn main() {
+    if let 0.. = 0 {}
+    if let .. = 0 {}
+}"#,
+        );
+    }
+
+    #[test]
+    fn range_inclusive_pattern_no_hints() {
+        check_with_config(
+            InlayHintsConfig { range_exclusive_hints: true, ..DISABLED_CONFIG },
+            r#"
+fn main() {
+    if let 0..=10 = 0 {}
+    if let ..=100 = 0 {}
+}"#,
+        );
+    }
+}