$env.config now always holds a record with only valid values (#7309)

# Description
Closes #7059. Rather than generate a new Record each time $env.config is
accessed (as described in that issue), instead `$env.config = ` now A)
parses the input record, then B) un-parses it into a clean Record with
only the valid values, and stores that as an env-var. The reasoning for
this is that I believe `config_to_nu_record()` (the method that performs
step B) will be useful in later PRs. (See below)

As a result, this also "fixes" the following "bug":
```
〉$env.config = 'butts'
$env.config is not a record
〉$env.config
butts
```
~~Instead, `$env.config = 'butts'` now turns `$env.config` into the
default (not the default config.nu, but `Config::default()`, which
notably has empty keybindings, color_config, menus and hooks vecs).~~

This doesn't attempt to fix #7110. cc @Kangaxx-0

# Example of new behaviour

OLD:
```
〉$env.config = ($env.config | merge { foo: 1 })
$env.config.foo is an unknown config setting
〉$env.config.foo
1
```
NEW:
```
〉$env.config = ($env.config | merge { foo: 1 })
Error:
  × Config record contains invalid values or unknown settings

Error:
  × Error while applying config changes
   ╭─[entry #1:1:1]
 1 │ $env.config = ($env.config | merge { foo: 1 })
   ·                                           ┬
   ·                                           ╰── $env.config.foo is an unknown config setting
   ╰────
  help: This value has been removed from your $env.config record.

〉$env.config.foo
Error: nu:🐚:column_not_found (link)

  × Cannot find column
   ╭─[entry #1:1:1]
 1 │ $env.config = ($env.config | merge { foo: 1 })
   ·                              ──┬──
   ·                                ╰── value originates here
   ╰────
   ╭─[entry #2:1:1]
 1 │ $env.config.foo
   ·             ─┬─
   ·              ╰── cannot find column 'foo'
   ╰────
```
# Example of new errors

OLD:
```
$env.config.cd.baz is an unknown config setting
$env.config.foo is an unknown config setting
$env.config.bar is an unknown config setting
$env.config.table.qux is an unknown config setting
$env.config.history.qux is an unknown config setting
```
NEW:
```
Error: 
  × Config record contains invalid values or unknown settings

Error:
  × Error while applying config changes
     ╭─[C:\Users\Leon\AppData\Roaming\nushell\config.nu:267:1]
 267 │     abbreviations: true # allows `cd s/o/f` to expand to `cd some/other/folder`
 268 │     baz: 3,
     ·          ┬
     ·          ╰── $env.config.cd.baz is an unknown config setting
 269 │   }
     ╰────
  help: This value has been removed from your $env.config record.

Error:
  × Error while applying config changes
     ╭─[C:\Users\Leon\AppData\Roaming\nushell\config.nu:269:1]
 269 │   }
 270 │   foo: 1,
     ·        ┬
     ·        ╰── $env.config.foo is an unknown config setting
 271 │   bar: 2,
     ╰────
  help: This value has been removed from your $env.config record.

Error:
  × Error while applying config changes
     ╭─[C:\Users\Leon\AppData\Roaming\nushell\config.nu:270:1]
 270 │   foo: 1,
 271 │   bar: 2,
     ·        ┬
     ·        ╰── $env.config.bar is an unknown config setting
     ╰────
  help: This value has been removed from your $env.config record.

Error:
  × Error while applying config changes
     ╭─[C:\Users\Leon\AppData\Roaming\nushell\config.nu:279:1]
 279 │     }
 280 │     qux: 4,
     ·          ┬
     ·          ╰── $env.config.table.qux is an unknown config setting
 281 │   }
     ╰────
  help: This value has been removed from your $env.config record.

Error:
  × Error while applying config changes
     ╭─[C:\Users\Leon\AppData\Roaming\nushell\config.nu:285:1]
 285 │     file_format: "plaintext" # "sqlite" or "plaintext"
 286 │  qux: 2
     ·       ┬
     ·       ╰── $env.config.history.qux is an unknown config setting
 287 │   }
     ╰────
  help: This value has been removed from your $env.config record.


```

# User-Facing Changes

See above.

# Tests + Formatting

Don't forget to add tests that cover your changes.

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

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

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

Cargo.lock

@@ -2776,6 +2776,8 @@ dependencies = [
  "indexmap",
  "miette",
  "nu-json",
+ "nu-path",
+ "nu-test-support",
  "nu-utils",
  "num-format",
  "serde",

crates/nu-protocol/Cargo.toml

@@ -12,6 +12,8 @@ version = "0.72.2"
 [dependencies]
 nu-utils = { path = "../nu-utils", version = "0.72.2"  }
 nu-json = { path = "../nu-json", version = "0.72.2"  }
+nu-path = { path = "../nu-path", version = "0.72.2"  } # Used for test support
+nu-test-support = { path = "../nu-test-support", version = "0.72.2"  }
 
 byte-unit = "4.0.9"
 chrono = { version="0.4.23", features= ["serde", "std"], default-features = false }

crates/nu-protocol/src/engine/engine_state.rs

@@ -236,10 +236,18 @@ impl EngineState {
                     // Updating existing overlay
                     for (k, v) in env.drain() {
                         if k == "config" {
-                            self.config = v.clone().into_config().unwrap_or_default();
+                            // Don't insert the record as the "config" env var as-is.
+                            // Instead, mutate a clone of it with into_config(), and put THAT in env_vars.
+                            let mut new_record = v.clone();
+                            let (config, error) = new_record.into_config(&self.config);
+                            self.config = config;
+                            env_vars.insert(k, new_record);
+                            if let Some(e) = error {
+                                return Err(e);
+                            }
+                        } else {
+                            env_vars.insert(k, v);
                         }
-
-                        env_vars.insert(k, v);
                     }
                 } else {
                     // Pushing a new overlay

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

@@ -1315,6 +1315,24 @@ impl Value {
         Value::Bool { val, span }
     }
 
+    pub fn record(cols: Vec<String>, vals: Vec<Value>, span: Span) -> Value {
+        Value::Record { cols, vals, span }
+    }
+
+    pub fn record_from_hashmap(map: &HashMap<String, Value>, span: Span) -> Value {
+        let mut cols = vec![];
+        let mut vals = vec![];
+        for (key, val) in map.iter() {
+            cols.push(key.clone());
+            vals.push(val.clone());
+        }
+        Value::record(cols, vals, span)
+    }
+
+    pub fn list(vals: Vec<Value>, span: Span) -> Value {
+        Value::List { vals, span }
+    }
+
     /// Note: Only use this for test data, *not* live data, as it will point into unknown source
     /// when used in errors.
     pub fn test_string(s: impl Into<String>) -> Value {

crates/nu-protocol/tests/into_config.rs

@@ -0,0 +1,101 @@
+use nu_test_support::{nu, nu_repl_code};
+
+#[test]
+fn config_is_mutable() {
+    let actual = nu!(cwd: ".", nu_repl_code(&[r"let-env config = { ls: { clickable_links: true } }",
+        "$env.config.ls.clickable_links = false;",
+        "$env.config.ls.clickable_links"]));
+
+    assert_eq!(actual.out, "false");
+}
+
+#[test]
+fn config_preserved_after_do() {
+    let actual = nu!(cwd: ".", nu_repl_code(&[r"let-env config = { ls: { clickable_links: true } }",
+        "do -i { $env.config.ls.clickable_links = false }",
+        "$env.config.ls.clickable_links"]));
+
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn config_affected_when_mutated() {
+    let actual = nu!(cwd: ".", nu_repl_code(&[r#"let-env config = { filesize: { metric: false, format:"auto" } }"#,
+        r#"$env.config = { filesize: { metric: true, format:"auto" } }"#,
+        "20mib | into string"]));
+
+    assert_eq!(actual.out, "21.0 MB");
+}
+
+#[test]
+fn config_affected_when_deep_mutated() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[
+        r#"source default_config.nu"#,
+        r#"$env.config.filesize.metric = true"#,
+        r#"20mib | into string"#]));
+
+    assert_eq!(actual.out, "21.0 MB");
+}
+
+#[test]
+fn config_add_unsupported_key() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[
+        r#"source default_config.nu"#,
+        r#"$env.config.foo = 2"#,
+        r#";"#]));
+
+    assert!(actual
+        .err
+        .contains("$env.config.foo is an unknown config setting"));
+}
+
+#[test]
+fn config_add_unsupported_type() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[r#"source default_config.nu"#,
+        r#"$env.config.ls = '' "#,
+        r#";"#]));
+
+    assert!(actual.err.contains("should be a record"));
+}
+
+#[test]
+fn config_add_unsupported_value() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[r#"source default_config.nu"#,
+        r#"$env.config.history.file_format = ''"#,
+        r#";"#]));
+
+    assert!(actual.err.contains(
+        "unrecognized $env.config.history.file_format ''; expected either 'sqlite' or 'plaintext'"
+    ));
+}
+
+#[test]
+#[ignore = "Figure out how to make test_bins::nu_repl() continue execution after shell errors"]
+fn config_unsupported_key_reverted() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[r#"source default_config.nu"#,
+        r#"$env.config.foo = 1"#,
+        r#"'foo' in $env.config"#]));
+
+    assert_eq!(actual.out, "false");
+}
+
+#[test]
+#[ignore = "Figure out how to make test_bins::nu_repl() continue execution after shell errors"]
+fn config_unsupported_type_reverted() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[r#" source default_config.nu"#,
+        r#"$env.config.ls = ''"#,
+        r#"$env.config.ls | describe"#]));
+
+    assert_eq!(actual.out, "record");
+}
+
+#[test]
+#[ignore = "Figure out how to make test_bins::nu_repl() continue execution after errors"]
+fn config_unsupported_value_reverted() {
+    let actual = nu!(cwd: "crates/nu-utils/src/sample_config", nu_repl_code(&[r#" source default_config.nu"#,
+        r#"$env.config.history.file_format = 'plaintext'"#,
+        r#"$env.config.history.file_format = ''"#,
+        r#"$env.config.history.file_format | to json"#]));
+
+    assert_eq!(actual.out, "\"plaintext\"");
+}