Use Value::coerce_bool in into bool (#14731)

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# Description
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I realized that the `into bool` command somehow implements a conversion
into a boolean value which was very similar to my implementation of
~`Value::as_env_bool`~ `Value::coerce_bool`. To streamline that behavior
a bit, I replaced most of the implementation of `into bool` with my
~`Value::as_env_bool`~ `Value::coerce_bool` method.

Also I added a new flag called `--relaxed` which lets the command behave
more closely to the ~`Value::as_env_bool`~ `Value::coerce_bool` method
as it allows null values and is more loose to strings. ~Which now begs
the question, should I rename `Value::as_env_bool` just to
`Value::coerce_bool` which would fit the `Value::coerce_str` method
name?~ (Renamed that.)

# User-Facing Changes
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The `into bool` command behaves the same but with `--relaxed` you can
also throw a `null` or some more strings at it which makes it more
ergonomic for env conversions.

# Tests + Formatting
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I added some more tests to see that the strict handling works and added
some more examples to the command to showcase the `--relaxed` flag which
also gets tested.

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

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@Bahex mentioned in #14704 that it broke the zoxide script, this PR
should help to fix the issue.

crates/nu-protocol/src/config/ansi_coloring.rs

@@ -48,7 +48,7 @@ impl UseAnsiColoring {
         let env_value = |env_name| {
             engine_state
                 .get_env_var_insensitive(env_name)
-                .and_then(Value::as_env_bool)
+                .and_then(|v| v.coerce_bool().ok())
                 .unwrap_or(false)
         };
 
@@ -61,7 +61,7 @@ impl UseAnsiColoring {
         }
 
         if let Some(cli_color) = engine_state.get_env_var_insensitive("clicolor") {
-            if let Some(cli_color) = cli_color.as_env_bool() {
+            if let Ok(cli_color) = cli_color.coerce_bool() {
                 return cli_color;
             }
         }

crates/nu-protocol/src/value/mod.rs

@@ -667,7 +667,7 @@ impl Value {
     ///
     /// The following rules are used:
     /// - Values representing `false`:
-    ///   - Empty strings
+    ///   - Empty strings or strings that equal to "false" in any case
     ///   - The number `0` (as an integer, float or string)
     ///   - `Nothing`
     ///   - Explicit boolean `false`
@@ -677,19 +677,19 @@ impl Value {
     ///   - Explicit boolean `true`
     ///
     /// For all other, more complex variants of [`Value`], the function cannot determine a
-    /// boolean representation and returns `None`.
-    pub fn as_env_bool(&self) -> Option<bool> {
+    /// boolean representation and returns `Err`.
+    pub fn coerce_bool(&self) -> Result<bool, ShellError> {
         match self {
-            Value::Bool { val: false, .. }
-            | Value::Int { val: 0, .. }
-            | Value::Float { val: 0.0, .. }
-            | Value::Nothing { .. } => Some(false),
-            Value::String { val, .. } => match val.as_str() {
-                "" | "0" => Some(false),
-                _ => Some(true),
+            Value::Bool { val: false, .. } | Value::Int { val: 0, .. } | Value::Nothing { .. } => {
+                Ok(false)
+            }
+            Value::Float { val, .. } if val <= &f64::EPSILON => Ok(false),
+            Value::String { val, .. } => match val.trim().to_ascii_lowercase().as_str() {
+                "" | "0" | "false" => Ok(false),
+                _ => Ok(true),
             },
-            Value::Bool { .. } | Value::Int { .. } | Value::Float { .. } => Some(true),
-            _ => None,
+            Value::Bool { .. } | Value::Int { .. } | Value::Float { .. } => Ok(true),
+            _ => self.cant_convert_to("bool"),
         }
     }
 
@@ -3916,39 +3916,36 @@ mod tests {
     #[test]
     fn test_env_as_bool() {
         // explicit false values
-        assert_eq!(Value::test_bool(false).as_env_bool(), Some(false));
-        assert_eq!(Value::test_int(0).as_env_bool(), Some(false));
-        assert_eq!(Value::test_float(0.0).as_env_bool(), Some(false));
-        assert_eq!(Value::test_string("").as_env_bool(), Some(false));
-        assert_eq!(Value::test_string("0").as_env_bool(), Some(false));
-        assert_eq!(Value::test_nothing().as_env_bool(), Some(false));
+        assert_eq!(Value::test_bool(false).coerce_bool(), Ok(false));
+        assert_eq!(Value::test_int(0).coerce_bool(), Ok(false));
+        assert_eq!(Value::test_float(0.0).coerce_bool(), Ok(false));
+        assert_eq!(Value::test_string("").coerce_bool(), Ok(false));
+        assert_eq!(Value::test_string("0").coerce_bool(), Ok(false));
+        assert_eq!(Value::test_nothing().coerce_bool(), Ok(false));
 
         // explicit true values
-        assert_eq!(Value::test_bool(true).as_env_bool(), Some(true));
-        assert_eq!(Value::test_int(1).as_env_bool(), Some(true));
-        assert_eq!(Value::test_float(1.0).as_env_bool(), Some(true));
-        assert_eq!(Value::test_string("1").as_env_bool(), Some(true));
+        assert_eq!(Value::test_bool(true).coerce_bool(), Ok(true));
+        assert_eq!(Value::test_int(1).coerce_bool(), Ok(true));
+        assert_eq!(Value::test_float(1.0).coerce_bool(), Ok(true));
+        assert_eq!(Value::test_string("1").coerce_bool(), Ok(true));
 
         // implicit true values
-        assert_eq!(Value::test_int(42).as_env_bool(), Some(true));
-        assert_eq!(Value::test_float(0.5).as_env_bool(), Some(true));
-        assert_eq!(Value::test_string("not zero").as_env_bool(), Some(true));
+        assert_eq!(Value::test_int(42).coerce_bool(), Ok(true));
+        assert_eq!(Value::test_float(0.5).coerce_bool(), Ok(true));
+        assert_eq!(Value::test_string("not zero").coerce_bool(), Ok(true));
 
         // complex values returning None
-        assert_eq!(Value::test_record(Record::default()).as_env_bool(), None);
-        assert_eq!(
-            Value::test_list(vec![Value::test_int(1)]).as_env_bool(),
-            None
-        );
-        assert_eq!(
-            Value::test_date(
-                chrono::DateTime::parse_from_rfc3339("2024-01-01T12:00:00+00:00").unwrap(),
-            )
-            .as_env_bool(),
-            None
-        );
-        assert_eq!(Value::test_glob("*.rs").as_env_bool(), None);
-        assert_eq!(Value::test_binary(vec![1, 2, 3]).as_env_bool(), None);
-        assert_eq!(Value::test_duration(3600).as_env_bool(), None);
+        assert!(Value::test_record(Record::default()).coerce_bool().is_err());
+        assert!(Value::test_list(vec![Value::test_int(1)])
+            .coerce_bool()
+            .is_err());
+        assert!(Value::test_date(
+            chrono::DateTime::parse_from_rfc3339("2024-01-01T12:00:00+00:00").unwrap(),
+        )
+        .coerce_bool()
+        .is_err());
+        assert!(Value::test_glob("*.rs").coerce_bool().is_err());
+        assert!(Value::test_binary(vec![1, 2, 3]).coerce_bool().is_err());
+        assert!(Value::test_duration(3600).coerce_bool().is_err());
     }
 }