Merge commit 'e18101137866b79045fee0ef996e696e68c920b4' into clippyup

6 files changed, 325 insertions, 142 deletions

diff --git a/src/tools/clippy/clippy_utils/src/camel_case.rs b/src/tools/clippy/clippy_utils/src/camel_case.rs
deleted file mode 100644
index a6636e39137..00000000000
--- a/src/tools/clippy/clippy_utils/src/camel_case.rs
+++ /dev/null
@@ -1,117 +0,0 @@
-/// Returns the index of the character after the first camel-case component of `s`.
-#[must_use]
-pub fn until(s: &str) -> usize {
-    let mut iter = s.char_indices();
-    if let Some((_, first)) = iter.next() {
-        if !first.is_uppercase() {
-            return 0;
-        }
-    } else {
-        return 0;
-    }
-    let mut up = true;
-    let mut last_i = 0;
-    for (i, c) in iter {
-        if up {
-            if c.is_lowercase() {
-                up = false;
-            } else {
-                return last_i;
-            }
-        } else if c.is_uppercase() {
-            up = true;
-            last_i = i;
-        } else if !c.is_lowercase() {
-            return i;
-        }
-    }
-    if up { last_i } else { s.len() }
-}
-
-/// Returns index of the last camel-case component of `s`.
-#[must_use]
-pub fn from(s: &str) -> usize {
-    let mut iter = s.char_indices().rev();
-    if let Some((_, first)) = iter.next() {
-        if !first.is_lowercase() {
-            return s.len();
-        }
-    } else {
-        return s.len();
-    }
-    let mut down = true;
-    let mut last_i = s.len();
-    for (i, c) in iter {
-        if down {
-            if c.is_uppercase() {
-                down = false;
-                last_i = i;
-            } else if !c.is_lowercase() {
-                return last_i;
-            }
-        } else if c.is_lowercase() {
-            down = true;
-        } else if c.is_uppercase() {
-            last_i = i;
-        } else {
-            return last_i;
-        }
-    }
-    last_i
-}
-
-#[cfg(test)]
-mod test {
-    use super::{from, until};
-
-    #[test]
-    fn from_full() {
-        assert_eq!(from("AbcDef"), 0);
-        assert_eq!(from("Abc"), 0);
-        assert_eq!(from("ABcd"), 0);
-        assert_eq!(from("ABcdEf"), 0);
-        assert_eq!(from("AabABcd"), 0);
-    }
-
-    #[test]
-    fn from_partial() {
-        assert_eq!(from("abcDef"), 3);
-        assert_eq!(from("aDbc"), 1);
-        assert_eq!(from("aabABcd"), 3);
-    }
-
-    #[test]
-    fn from_not() {
-        assert_eq!(from("AbcDef_"), 7);
-        assert_eq!(from("AbcDD"), 5);
-    }
-
-    #[test]
-    fn from_caps() {
-        assert_eq!(from("ABCD"), 4);
-    }
-
-    #[test]
-    fn until_full() {
-        assert_eq!(until("AbcDef"), 6);
-        assert_eq!(until("Abc"), 3);
-    }
-
-    #[test]
-    fn until_not() {
-        assert_eq!(until("abcDef"), 0);
-        assert_eq!(until("aDbc"), 0);
-    }
-
-    #[test]
-    fn until_partial() {
-        assert_eq!(until("AbcDef_"), 6);
-        assert_eq!(until("CallTypeC"), 8);
-        assert_eq!(until("AbcDD"), 3);
-    }
-
-    #[test]
-    fn until_caps() {
-        assert_eq!(until("ABCD"), 0);
-    }
-}
diff --git a/src/tools/clippy/clippy_utils/src/consts.rs b/src/tools/clippy/clippy_utils/src/consts.rs
index 8bf31807d55..04347672e0f 100644
--- a/src/tools/clippy/clippy_utils/src/consts.rs
+++ b/src/tools/clippy/clippy_utils/src/consts.rs
@@ -155,6 +155,19 @@ impl Constant {
             _ => None,
         }
     }
+
+    /// Returns the integer value or `None` if `self` or `val_type` is not integer type.
+    pub fn int_value(&self, cx: &LateContext<'_>, val_type: Ty<'_>) -> Option<FullInt> {
+        if let Constant::Int(const_int) = *self {
+            match *val_type.kind() {
+                ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
+                ty::Uint(_) => Some(FullInt::U(const_int)),
+                _ => None,
+            }
+        } else {
+            None
+        }
+    }
 }
 
 /// Parses a `LitKind` to a `Constant`.
@@ -202,6 +215,52 @@ pub fn constant_simple<'tcx>(
     constant(lcx, typeck_results, e).and_then(|(cst, res)| if res { None } else { Some(cst) })
 }
 
+pub fn constant_full_int(
+    lcx: &LateContext<'tcx>,
+    typeck_results: &ty::TypeckResults<'tcx>,
+    e: &Expr<'_>,
+) -> Option<FullInt> {
+    constant_simple(lcx, typeck_results, e)?.int_value(lcx, typeck_results.expr_ty(e))
+}
+
+#[derive(Copy, Clone, Debug, Eq)]
+pub enum FullInt {
+    S(i128),
+    U(u128),
+}
+
+impl PartialEq for FullInt {
+    #[must_use]
+    fn eq(&self, other: &Self) -> bool {
+        self.cmp(other) == Ordering::Equal
+    }
+}
+
+impl PartialOrd for FullInt {
+    #[must_use]
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for FullInt {
+    #[must_use]
+    fn cmp(&self, other: &Self) -> Ordering {
+        use FullInt::{S, U};
+
+        fn cmp_s_u(s: i128, u: u128) -> Ordering {
+            u128::try_from(s).map_or(Ordering::Less, |x| x.cmp(&u))
+        }
+
+        match (*self, *other) {
+            (S(s), S(o)) => s.cmp(&o),
+            (U(s), U(o)) => s.cmp(&o),
+            (S(s), U(o)) => cmp_s_u(s, o),
+            (U(s), S(o)) => cmp_s_u(o, s).reverse(),
+        }
+    }
+}
+
 /// Creates a `ConstEvalLateContext` from the given `LateContext` and `TypeckResults`.
 pub fn constant_context<'a, 'tcx>(
     lcx: &'a LateContext<'tcx>,
diff --git a/src/tools/clippy/clippy_utils/src/diagnostics.rs b/src/tools/clippy/clippy_utils/src/diagnostics.rs
index 9302e5c21fa..d47b002ad7a 100644
--- a/src/tools/clippy/clippy_utils/src/diagnostics.rs
+++ b/src/tools/clippy/clippy_utils/src/diagnostics.rs
@@ -72,7 +72,7 @@ pub fn span_lint<T: LintContext>(cx: &T, lint: &'static Lint, sp: impl Into<Mult
 /// 6  |     let other_f64_nan = 0.0f64 / 0.0;
 ///    |                         ^^^^^^^^^^^^
 ///    |
-///    = help: Consider using `f64::NAN` if you would like a constant representing NaN
+///    = help: consider using `f64::NAN` if you would like a constant representing NaN
 /// ```
 pub fn span_lint_and_help<'a, T: LintContext>(
     cx: &'a T,
diff --git a/src/tools/clippy/clippy_utils/src/higher.rs b/src/tools/clippy/clippy_utils/src/higher.rs
index 60c4cb361aa..b3a9a1de2ec 100644
--- a/src/tools/clippy/clippy_utils/src/higher.rs
+++ b/src/tools/clippy/clippy_utils/src/higher.rs
@@ -1,14 +1,14 @@
-//! This module contains functions that retrieves specifiec elements.
+//! This module contains functions that retrieve specific elements.
 
 #![deny(clippy::missing_docs_in_private_items)]
 
 use crate::ty::is_type_diagnostic_item;
-use crate::{is_expn_of, last_path_segment, match_def_path, paths};
+use crate::{is_expn_of, last_path_segment, match_def_path, path_to_local_id, paths};
 use if_chain::if_chain;
 use rustc_ast::ast::{self, LitKind};
 use rustc_hir as hir;
 use rustc_hir::{
-    Arm, Block, BorrowKind, Expr, ExprKind, HirId, LoopSource, MatchSource, Node, Pat, QPath, StmtKind, UnOp,
+    Arm, Block, BorrowKind, Expr, ExprKind, HirId, LoopSource, MatchSource, Node, Pat, PatKind, QPath, StmtKind, UnOp,
 };
 use rustc_lint::LateContext;
 use rustc_span::{sym, symbol, ExpnKind, Span, Symbol};
@@ -513,6 +513,8 @@ pub struct FormatArgsExpn<'tcx> {
     pub format_string_parts: &'tcx [Expr<'tcx>],
     /// Symbols corresponding to [`Self::format_string_parts`]
     pub format_string_symbols: Vec<Symbol>,
+    /// Match arm patterns, the `arg0`, etc. from the next field `args`
+    pub arg_names: &'tcx [Pat<'tcx>],
     /// Expressions like `ArgumentV1::new(arg0, Debug::fmt)`
     pub args: &'tcx [Expr<'tcx>],
     /// The final argument passed to `Arguments::new_v1_formatted`, if applicable
@@ -557,6 +559,7 @@ impl FormatArgsExpn<'tcx> {
                     _ => None,
                 })
                 .collect();
+            if let PatKind::Tuple(arg_names, None) = arm.pat.kind;
             if let ExprKind::Array(args) = arm.body.kind;
             then {
                 Some(FormatArgsExpn {
@@ -564,6 +567,7 @@ impl FormatArgsExpn<'tcx> {
                     value_args,
                     format_string_parts,
                     format_string_symbols,
+                    arg_names,
                     args,
                     fmt_expr,
                 })
@@ -587,9 +591,15 @@ impl FormatArgsExpn<'tcx> {
                             if let Some(position_field) = fields.iter().find(|f| f.ident.name == sym::position);
                             if let ExprKind::Lit(lit) = &position_field.expr.kind;
                             if let LitKind::Int(position, _) = lit.node;
+                            if let Ok(i) = usize::try_from(position);
+                            let arg = &self.args[i];
+                            if let ExprKind::Call(_, [arg_name, _]) = arg.kind;
+                            if let Some(j) = self
+                                .arg_names
+                                .iter()
+                                .position(|pat| path_to_local_id(arg_name, pat.hir_id));
                             then {
-                                let i = usize::try_from(position).unwrap();
-                                Some(FormatArgsArg { value: self.value_args[i], arg: &self.args[i], fmt: Some(fmt) })
+                                Some(FormatArgsArg { value: self.value_args[j], arg, fmt: Some(fmt) })
                             } else {
                                 None
                             }
@@ -718,9 +728,7 @@ impl PanicExpn<'tcx> {
     /// Parses an expanded `panic!` invocation
     pub fn parse(expr: &'tcx Expr<'tcx>) -> Option<Self> {
         if_chain! {
-            if let ExprKind::Block(block, _) = expr.kind;
-            if let Some(init) = block.expr;
-            if let ExprKind::Call(_, [format_args]) = init.kind;
+            if let ExprKind::Call(_, [format_args]) = expr.kind;
             let expn_data = expr.span.ctxt().outer_expn_data();
             if let Some(format_args) = FormatArgsExpn::parse(format_args);
             then {
@@ -770,13 +778,13 @@ pub fn get_vec_init_kind<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -
                     }
                     return Some(VecInitKind::WithExprCapacity(arg.hir_id));
                 }
-            }
+            },
             ExprKind::Path(QPath::Resolved(_, path))
                 if match_def_path(cx, path.res.opt_def_id()?, &paths::DEFAULT_TRAIT_METHOD)
                     && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::Vec) =>
             {
                 return Some(VecInitKind::Default);
-            }
+            },
             _ => (),
         }
     }
diff --git a/src/tools/clippy/clippy_utils/src/lib.rs b/src/tools/clippy/clippy_utils/src/lib.rs
index 9bc380ca6ca..086fbc9d3dd 100644
--- a/src/tools/clippy/clippy_utils/src/lib.rs
+++ b/src/tools/clippy/clippy_utils/src/lib.rs
@@ -37,7 +37,6 @@ pub mod sym_helper;
 #[allow(clippy::module_name_repetitions)]
 pub mod ast_utils;
 pub mod attrs;
-pub mod camel_case;
 pub mod comparisons;
 pub mod consts;
 pub mod diagnostics;
@@ -50,6 +49,7 @@ pub mod paths;
 pub mod ptr;
 pub mod qualify_min_const_fn;
 pub mod source;
+pub mod str_utils;
 pub mod sugg;
 pub mod ty;
 pub mod usage;
@@ -712,7 +712,7 @@ pub fn is_default_equivalent(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
 /// Checks if the top level expression can be moved into a closure as is.
 /// Currently checks for:
 /// * Break/Continue outside the given loop HIR ids.
-/// * Yield/Return statments.
+/// * Yield/Return statements.
 /// * Inline assembly.
 /// * Usages of a field of a local where the type of the local can be partially moved.
 ///
@@ -844,10 +844,13 @@ pub fn capture_local_usage(cx: &LateContext<'tcx>, e: &Expr<'_>) -> CaptureKind
     let mut capture_expr_ty = e;
 
     for (parent_id, parent) in cx.tcx.hir().parent_iter(e.hir_id) {
-        if let [Adjustment {
-            kind: Adjust::Deref(_) | Adjust::Borrow(AutoBorrow::Ref(..)),
-            target,
-        }, ref adjust @ ..] = *cx
+        if let [
+            Adjustment {
+                kind: Adjust::Deref(_) | Adjust::Borrow(AutoBorrow::Ref(..)),
+                target,
+            },
+            ref adjust @ ..,
+        ] = *cx
             .typeck_results()
             .adjustments()
             .get(child_id)
@@ -1232,9 +1235,7 @@ pub fn get_enclosing_loop_or_closure(tcx: TyCtxt<'tcx>, expr: &Expr<'_>) -> Opti
     for (_, node) in tcx.hir().parent_iter(expr.hir_id) {
         match node {
             Node::Expr(
-                e
-                @
-                Expr {
+                e @ Expr {
                     kind: ExprKind::Loop(..) | ExprKind::Closure(..),
                     ..
                 },
@@ -1692,10 +1693,12 @@ pub fn is_async_fn(kind: FnKind<'_>) -> bool {
 pub fn get_async_fn_body(tcx: TyCtxt<'tcx>, body: &Body<'_>) -> Option<&'tcx Expr<'tcx>> {
     if let ExprKind::Call(
         _,
-        &[Expr {
-            kind: ExprKind::Closure(_, _, body, _, _),
-            ..
-        }],
+        &[
+            Expr {
+                kind: ExprKind::Closure(_, _, body, _, _),
+                ..
+            },
+        ],
     ) = body.value.kind
     {
         if let ExprKind::Block(
@@ -2123,7 +2126,7 @@ pub fn is_in_test_function(tcx: TyCtxt<'_>, id: hir::HirId) -> bool {
     vis.found
 }
 
-/// Checks whether item either has `test` attribute appelied, or
+/// Checks whether item either has `test` attribute applied, or
 /// is a module with `test` in its name.
 ///
 /// Note: If you use this function, please add a `#[test]` case in `tests/ui_test`.
diff --git a/src/tools/clippy/clippy_utils/src/str_utils.rs b/src/tools/clippy/clippy_utils/src/str_utils.rs
new file mode 100644
index 00000000000..cba96e05a24
--- /dev/null
+++ b/src/tools/clippy/clippy_utils/src/str_utils.rs
@@ -0,0 +1,230 @@
+/// Dealing with sting indices can be hard, this struct ensures that both the
+/// character and byte index are provided for correct indexing.
+#[derive(Debug, Default, PartialEq, Eq)]
+pub struct StrIndex {
+    pub char_index: usize,
+    pub byte_index: usize,
+}
+
+impl StrIndex {
+    pub fn new(char_index: usize, byte_index: usize) -> Self {
+        Self { char_index, byte_index }
+    }
+}
+
+/// Returns the index of the character after the first camel-case component of `s`.
+///
+/// ```
+/// assert_eq!(camel_case_until("AbcDef"), StrIndex::new(6, 6));
+/// assert_eq!(camel_case_until("ABCD"), StrIndex::new(0, 0));
+/// assert_eq!(camel_case_until("AbcDD"), StrIndex::new(3, 3));
+/// assert_eq!(camel_case_until("Abc\u{f6}\u{f6}DD"), StrIndex::new(5, 7));
+/// ```
+#[must_use]
+pub fn camel_case_until(s: &str) -> StrIndex {
+    let mut iter = s.char_indices().enumerate();
+    if let Some((_char_index, (_, first))) = iter.next() {
+        if !first.is_uppercase() {
+            return StrIndex::new(0, 0);
+        }
+    } else {
+        return StrIndex::new(0, 0);
+    }
+    let mut up = true;
+    let mut last_index = StrIndex::new(0, 0);
+    for (char_index, (byte_index, c)) in iter {
+        if up {
+            if c.is_lowercase() {
+                up = false;
+            } else {
+                return last_index;
+            }
+        } else if c.is_uppercase() {
+            up = true;
+            last_index.byte_index = byte_index;
+            last_index.char_index = char_index;
+        } else if !c.is_lowercase() {
+            return StrIndex::new(char_index, byte_index);
+        }
+    }
+
+    if up {
+        last_index
+    } else {
+        StrIndex::new(s.chars().count(), s.len())
+    }
+}
+
+/// Returns index of the last camel-case component of `s`.
+///
+/// ```
+/// assert_eq!(camel_case_start("AbcDef"), StrIndex::new(0, 0));
+/// assert_eq!(camel_case_start("abcDef"), StrIndex::new(3, 3));
+/// assert_eq!(camel_case_start("ABCD"), StrIndex::new(4, 4));
+/// assert_eq!(camel_case_start("abcd"), StrIndex::new(4, 4));
+/// assert_eq!(camel_case_start("\u{f6}\u{f6}cd"), StrIndex::new(4, 6));
+/// ```
+#[must_use]
+pub fn camel_case_start(s: &str) -> StrIndex {
+    let char_count = s.chars().count();
+    let range = 0..char_count;
+    let mut iter = range.rev().zip(s.char_indices().rev());
+    if let Some((char_index, (_, first))) = iter.next() {
+        if !first.is_lowercase() {
+            return StrIndex::new(char_index, s.len());
+        }
+    } else {
+        return StrIndex::new(char_count, s.len());
+    }
+    let mut down = true;
+    let mut last_index = StrIndex::new(char_count, s.len());
+    for (char_index, (byte_index, c)) in iter {
+        if down {
+            if c.is_uppercase() {
+                down = false;
+                last_index.byte_index = byte_index;
+                last_index.char_index = char_index;
+            } else if !c.is_lowercase() {
+                return last_index;
+            }
+        } else if c.is_lowercase() {
+            down = true;
+        } else if c.is_uppercase() {
+            last_index.byte_index = byte_index;
+            last_index.char_index = char_index;
+        } else {
+            return last_index;
+        }
+    }
+    last_index
+}
+
+/// Dealing with sting comparison can be complicated, this struct ensures that both the
+/// character and byte count are provided for correct indexing.
+#[derive(Debug, Default, PartialEq, Eq)]
+pub struct StrCount {
+    pub char_count: usize,
+    pub byte_count: usize,
+}
+
+impl StrCount {
+    pub fn new(char_count: usize, byte_count: usize) -> Self {
+        Self { char_count, byte_count }
+    }
+}
+
+/// Returns the number of chars that match from the start
+///
+/// ```
+/// assert_eq!(count_match_start("hello_mouse", "hello_penguin"), StrCount::new(6, 6));
+/// assert_eq!(count_match_start("hello_clippy", "bye_bugs"), StrCount::new(0, 0));
+/// assert_eq!(count_match_start("hello_world", "hello_world"), StrCount::new(11, 11));
+/// assert_eq!(count_match_start("T\u{f6}ffT\u{f6}ff", "T\u{f6}ff"), StrCount::new(4, 5));
+/// ```
+#[must_use]
+pub fn count_match_start(str1: &str, str2: &str) -> StrCount {
+    // (char_index, char1)
+    let char_count = str1.chars().count();
+    let iter1 = (0..=char_count).zip(str1.chars());
+    // (byte_index, char2)
+    let iter2 = str2.char_indices();
+
+    iter1
+        .zip(iter2)
+        .take_while(|((_, c1), (_, c2))| c1 == c2)
+        .last()
+        .map_or_else(StrCount::default, |((char_index, _), (byte_index, character))| {
+            StrCount::new(char_index + 1, byte_index + character.len_utf8())
+        })
+}
+
+/// Returns the number of chars and bytes that match from the end
+///
+/// ```
+/// assert_eq!(count_match_end("hello_cat", "bye_cat"), StrCount::new(4, 4));
+/// assert_eq!(count_match_end("if_item_thing", "enum_value"), StrCount::new(0, 0));
+/// assert_eq!(count_match_end("Clippy", "Clippy"), StrCount::new(6, 6));
+/// assert_eq!(count_match_end("MyT\u{f6}ff", "YourT\u{f6}ff"), StrCount::new(4, 5));
+/// ```
+#[must_use]
+pub fn count_match_end(str1: &str, str2: &str) -> StrCount {
+    let char_count = str1.chars().count();
+    if char_count == 0 {
+        return StrCount::default();
+    }
+
+    // (char_index, char1)
+    let iter1 = (0..char_count).rev().zip(str1.chars().rev());
+    // (byte_index, char2)
+    let byte_count = str2.len();
+    let iter2 = str2.char_indices().rev();
+
+    iter1
+        .zip(iter2)
+        .take_while(|((_, c1), (_, c2))| c1 == c2)
+        .last()
+        .map_or_else(StrCount::default, |((char_index, _), (byte_index, _))| {
+            StrCount::new(char_count - char_index, byte_count - byte_index)
+        })
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn camel_case_start_full() {
+        assert_eq!(camel_case_start("AbcDef"), StrIndex::new(0, 0));
+        assert_eq!(camel_case_start("Abc"), StrIndex::new(0, 0));
+        assert_eq!(camel_case_start("ABcd"), StrIndex::new(0, 0));
+        assert_eq!(camel_case_start("ABcdEf"), StrIndex::new(0, 0));
+        assert_eq!(camel_case_start("AabABcd"), StrIndex::new(0, 0));
+    }
+
+    #[test]
+    fn camel_case_start_partial() {
+        assert_eq!(camel_case_start("abcDef"), StrIndex::new(3, 3));
+        assert_eq!(camel_case_start("aDbc"), StrIndex::new(1, 1));
+        assert_eq!(camel_case_start("aabABcd"), StrIndex::new(3, 3));
+        assert_eq!(camel_case_start("\u{f6}\u{f6}AabABcd"), StrIndex::new(2, 4));
+    }
+
+    #[test]
+    fn camel_case_start_not() {
+        assert_eq!(camel_case_start("AbcDef_"), StrIndex::new(7, 7));
+        assert_eq!(camel_case_start("AbcDD"), StrIndex::new(5, 5));
+        assert_eq!(camel_case_start("all_small"), StrIndex::new(9, 9));
+        assert_eq!(camel_case_start("\u{f6}_all_small"), StrIndex::new(11, 12));
+    }
+
+    #[test]
+    fn camel_case_start_caps() {
+        assert_eq!(camel_case_start("ABCD"), StrIndex::new(4, 4));
+    }
+
+    #[test]
+    fn camel_case_until_full() {
+        assert_eq!(camel_case_until("AbcDef"), StrIndex::new(6, 6));
+        assert_eq!(camel_case_until("Abc"), StrIndex::new(3, 3));
+        assert_eq!(camel_case_until("Abc\u{f6}\u{f6}\u{f6}"), StrIndex::new(6, 9));
+    }
+
+    #[test]
+    fn camel_case_until_not() {
+        assert_eq!(camel_case_until("abcDef"), StrIndex::new(0, 0));
+        assert_eq!(camel_case_until("aDbc"), StrIndex::new(0, 0));
+    }
+
+    #[test]
+    fn camel_case_until_partial() {
+        assert_eq!(camel_case_until("AbcDef_"), StrIndex::new(6, 6));
+        assert_eq!(camel_case_until("CallTypeC"), StrIndex::new(8, 8));
+        assert_eq!(camel_case_until("AbcDD"), StrIndex::new(3, 3));
+        assert_eq!(camel_case_until("Abc\u{f6}\u{f6}DD"), StrIndex::new(5, 7));
+    }
+
+    #[test]
+    fn until_caps() {
+        assert_eq!(camel_case_until("ABCD"), StrIndex::new(0, 0));
+    }
+}