Protocol: debug_assert!() Span to reflect a valid slice (#6806)

Also enforce this by #[non_exhaustive] span such that going forward we
cannot, in debug builds (1), construct invalid spans.

The motivation for this stems from #6431 where I've seen crashes due to
invalid slice indexing.

My hope is this will mitigate such senarios

1. https://github.com/nushell/nushell/pull/6431#issuecomment-1278147241

# Description

(description of your pull request here)

# Tests

Make sure you've done the following:

- [ ] Add tests that cover your changes, either in the command examples,
the crate/tests folder, or in the /tests folder.
- [ ] Try to think about corner cases and various ways how your changes
could break. Cover them with tests.
- [ ] If adding tests is not possible, please document in the PR body a
minimal example with steps on how to reproduce so one can verify your
change works.

Make sure you've run and fixed any issues with these commands:

- [x] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [ ] `cargo clippy --workspace --features=extra -- -D warnings -D
clippy::unwrap_used -A clippy::needless_collect` to check that you're
using the standard code style
- [ ] `cargo test --workspace --features=extra` to check that all the
tests pass

# Documentation

- [ ] If your PR touches a user-facing nushell feature then make sure
that there is an entry in the documentation
(https://github.com/nushell/nushell.github.io) for the feature, and
update it if necessary.

crates/nu-command/src/charting/hashable_value.rs

@@ -53,7 +53,7 @@ impl Default for HashableValue {
     fn default() -> Self {
         HashableValue::Bool {
             val: false,
-            span: Span { start: 0, end: 0 },
+            span: Span::unknown(),
         }
     }
 }
@@ -214,7 +214,7 @@ mod test {
         ];
         for (val, expect_hashable_val) in values.into_iter() {
             assert_eq!(
-                HashableValue::from_value(val, Span { start: 0, end: 0 }).unwrap(),
+                HashableValue::from_value(val, Span::unknown()).unwrap(),
                 expect_hashable_val
             );
         }
@@ -245,7 +245,7 @@ mod test {
             },
         ];
         for v in values {
-            assert!(HashableValue::from_value(v, Span { start: 0, end: 0 }).is_err())
+            assert!(HashableValue::from_value(v, Span::unknown()).is_err())
         }
     }
 
@@ -266,7 +266,7 @@ mod test {
         for val in values.into_iter() {
             let expected_val = val.clone();
             assert_eq!(
-                HashableValue::from_value(val, Span { start: 0, end: 0 })
+                HashableValue::from_value(val, Span::unknown())
                     .unwrap()
                     .into_value(),
                 expected_val
@@ -279,14 +279,11 @@ mod test {
         assert_eq!(
             HashableValue::Bool {
                 val: true,
-                span: Span { start: 0, end: 1 }
+                span: Span::new(0, 1)
             },
             HashableValue::Bool {
                 val: true,
-                span: Span {
-                    start: 90,
-                    end: 1000
-                }
+                span: Span::new(90, 1000)
             }
         )
     }
@@ -299,7 +296,7 @@ mod test {
         assert!(set.contains(&HashableValue::Bool { val: true, span }));
 
         // hashable value doesn't care about span.
-        let diff_span = Span { start: 1, end: 2 };
+        let diff_span = Span::new(1, 2);
         set.insert(HashableValue::Bool {
             val: true,
             span: diff_span,

crates/nu-command/src/conversions/into/duration.rs

@@ -502,7 +502,7 @@ mod test {
 
     #[test]
     fn turns_ns_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 2);
         let word = Value::test_string("3ns");
         let expected = Value::Duration { val: 3, span };
         let convert_duration = None;
@@ -513,7 +513,7 @@ mod test {
 
     #[test]
     fn turns_us_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 2);
         let word = Value::test_string("4us");
         let expected = Value::Duration {
             val: 4 * 1000,
@@ -527,7 +527,7 @@ mod test {
 
     #[test]
     fn turns_ms_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 2);
         let word = Value::test_string("5ms");
         let expected = Value::Duration {
             val: 5 * 1000 * 1000,
@@ -541,7 +541,7 @@ mod test {
 
     #[test]
     fn turns_sec_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 3);
         let word = Value::test_string("1sec");
         let expected = Value::Duration {
             val: 1000 * 1000 * 1000,
@@ -555,7 +555,7 @@ mod test {
 
     #[test]
     fn turns_min_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 3);
         let word = Value::test_string("7min");
         let expected = Value::Duration {
             val: 7 * 60 * 1000 * 1000 * 1000,
@@ -569,7 +569,7 @@ mod test {
 
     #[test]
     fn turns_hr_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 3);
         let word = Value::test_string("42hr");
         let expected = Value::Duration {
             val: 42 * 60 * 60 * 1000 * 1000 * 1000,
@@ -583,7 +583,7 @@ mod test {
 
     #[test]
     fn turns_day_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 5);
         let word = Value::test_string("123day");
         let expected = Value::Duration {
             val: 123 * 24 * 60 * 60 * 1000 * 1000 * 1000,
@@ -597,7 +597,7 @@ mod test {
 
     #[test]
     fn turns_wk_to_duration() {
-        let span = Span::test_data();
+        let span = Span::new(0, 2);
         let word = Value::test_string("3wk");
         let expected = Value::Duration {
             val: 3 * 7 * 24 * 60 * 60 * 1000 * 1000 * 1000,

crates/nu-command/src/core_commands/error_make.rs

@@ -108,10 +108,7 @@ fn make_error(value: &Value, throw_span: Option<Span>) -> Option<ShellError> {
                     ) => Some(ShellError::GenericError(
                         message,
                         label_text,
-                        Some(Span {
-                            start: start as usize,
-                            end: end as usize,
-                        }),
+                        Some(Span::new(start as usize, end as usize)),
                         None,
                         Vec::new(),
                     )),

crates/nu-command/src/dataframe/values/nu_dataframe/mod.rs

@@ -39,7 +39,7 @@ impl Display for DataFrameValue {
 impl Default for DataFrameValue {
     fn default() -> Self {
         Self(Value::Nothing {
-            span: Span { start: 0, end: 0 },
+            span: Span::unknown(),
         })
     }
 }

crates/nu-command/src/env/config/config_env.rs

@@ -64,7 +64,7 @@ impl Command for ConfigEnv {
 
         let args = vec![Spanned {
             item: nu_config.to_string_lossy().to_string(),
-            span: Span { start: 0, end: 0 },
+            span: Span::unknown(),
         }];
 
         let command = ExternalCommand {

crates/nu-command/src/env/config/config_nu.rs

@@ -64,7 +64,7 @@ impl Command for ConfigNu {
 
         let args = vec![Spanned {
             item: nu_config.to_string_lossy().to_string(),
-            span: Span { start: 0, end: 0 },
+            span: Span::unknown(),
         }];
 
         let command = ExternalCommand {

crates/nu-command/src/filesystem/ls.rs

@@ -518,7 +518,7 @@ pub(crate) fn dir_entry_dict(
 
         if md.is_dir() {
             if du {
-                let params = DirBuilder::new(Span { start: 0, end: 2 }, None, false, None, false);
+                let params = DirBuilder::new(Span::new(0, 2), None, false, None, false);
                 let dir_size = DirInfo::new(filename, &params, None, ctrl_c).get_size();
 
                 vals.push(Value::Filesize {

crates/nu-command/src/filesystem/rm.rs

@@ -199,18 +199,18 @@ fn rm(
         ));
     }
 
-    let targets_span = Span {
-        start: targets
+    let targets_span = Span::new(
+        targets
             .iter()
             .map(|x| x.span.start)
             .min()
             .expect("targets were empty"),
-        end: targets
+        targets
             .iter()
             .map(|x| x.span.end)
             .max()
             .expect("targets were empty"),
-    };
+    );
 
     let path = current_dir(engine_state, stack)?;
 

crates/nu-command/src/filters/uniq_by.rs

@@ -154,7 +154,7 @@ fn item_mapper_by_col(cols: Vec<String>) -> impl Fn(crate::ItemMapperState) -> c
 
         let col_vals = Value::List {
             vals: item_column_values,
-            span: Span { start: 0, end: 0 },
+            span: Span::unknown(),
         };
 
         crate::ValueCounter::new_vals_to_compare(ms.item, ms.flag_ignore_case, col_vals)

crates/nu-command/src/formats/from/json.rs

@@ -166,19 +166,13 @@ fn convert_row_column_to_span(row: usize, col: usize, contents: &str) -> Span {
             cur_col = 0;
         }
         if cur_row >= row && cur_col >= col {
-            return Span {
-                start: offset,
-                end: offset,
-            };
+            return Span::new(offset, offset);
         } else {
             cur_col += 1;
         }
     }
 
-    Span {
-        start: contents.len(),
-        end: contents.len(),
-    }
+    Span::new(contents.len(), contents.len())
 }
 
 fn convert_string_to_value(string_input: String, span: Span) -> Result<Value, ShellError> {

crates/nu-command/src/misc/tutor.rs

@@ -420,11 +420,11 @@ fn display(help: &str, engine_state: &EngineState, stack: &mut Stack, span: Span
                     &Call::new(span),
                     Value::String {
                         val: item.to_string(),
-                        span: Span { start: 0, end: 0 },
+                        span: Span::unknown(),
                     }
                     .into_pipeline_data(),
                 ) {
-                    let result = output.into_value(Span { start: 0, end: 0 });
+                    let result = output.into_value(Span::unknown());
                     match result.as_string() {
                         Ok(s) => {
                             build.push_str(&s);

crates/nu-command/src/strings/format/command.rs

@@ -152,18 +152,12 @@ fn extract_formatting_operations(input: String, span_start: usize) -> Vec<Format
             if column_need_eval {
                 output.push(FormatOperation::ValueNeedEval(
                     column_name.clone(),
-                    Span {
-                        start: span_start + column_span_start,
-                        end: span_start + column_span_end,
-                    },
+                    Span::new(span_start + column_span_start, span_start + column_span_end),
                 ));
             } else {
                 output.push(FormatOperation::ValueFromColumn(
                     column_name.clone(),
-                    Span {
-                        start: span_start + column_span_start,
-                        end: span_start + column_span_end,
-                    },
+                    Span::new(span_start + column_span_start, span_start + column_span_end),
                 ));
             }
         }