Add FILE_PWD environment variable when running 'nu script.nu' (#7424)

# Description

When running `nu script.nu`, the `$env.FILE_PWD` will be set to the
directory where the script is.

Also makes the error message a bit nicer:
```
> target/debug/nu asdihga
Error: nu:🐚:file_not_found (link)

  × File not found
   ╭─[source:1:1]
 1 │ nu
   · ▲
   · ╰── Could not access file 'asdihga': "No such file or directory (os error 2)"
   ╰────

```

# User-Facing Changes

`FILE_PWD` environment variable is available when running a script as
`nu script.nu`.

# 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.

crates/nu-cli/src/eval_file.rs

@@ -2,13 +2,13 @@ use crate::util::{eval_source, report_error};
 use log::info;
 use log::trace;
 use miette::{IntoDiagnostic, Result};
-use nu_engine::convert_env_values;
+use nu_engine::{convert_env_values, current_dir};
 use nu_parser::parse;
-use nu_protocol::Type;
+use nu_path::canonicalize_with;
 use nu_protocol::{
     ast::Call,
     engine::{EngineState, Stack, StateWorkingSet},
-    Config, PipelineData, Span, Value,
+    Config, PipelineData, ShellError, Span, Type, Value,
 };
 use nu_utils::stdout_write_all_and_flush;
 
@@ -27,25 +27,92 @@ pub fn evaluate_file(
         std::process::exit(1);
     }
 
-    let file = std::fs::read(&path).into_diagnostic()?;
+    let cwd = current_dir(engine_state, stack)?;
 
-    engine_state.start_in_file(Some(&path));
+    let file_path = {
+        match canonicalize_with(&path, &cwd) {
+            Ok(p) => p,
+            Err(e) => {
+                let working_set = StateWorkingSet::new(engine_state);
+                report_error(
+                    &working_set,
+                    &ShellError::FileNotFoundCustom(
+                        format!("Could not access file '{}': {:?}", path, e.to_string()),
+                        Span::unknown(),
+                    ),
+                );
+                std::process::exit(1);
+            }
+        }
+    };
+
+    let file_path_str = match file_path.to_str() {
+        Some(s) => s,
+        None => {
+            let working_set = StateWorkingSet::new(engine_state);
+            report_error(
+                &working_set,
+                &ShellError::NonUtf8Custom(
+                    format!(
+                        "Input file name '{}' is not valid UTF8",
+                        file_path.to_string_lossy()
+                    ),
+                    Span::unknown(),
+                ),
+            );
+            std::process::exit(1);
+        }
+    };
+
+    let file = match std::fs::read(&file_path).into_diagnostic() {
+        Ok(p) => p,
+        Err(e) => {
+            let working_set = StateWorkingSet::new(engine_state);
+            report_error(
+                &working_set,
+                &ShellError::FileNotFoundCustom(
+                    format!(
+                        "Could not read file '{}': {:?}",
+                        file_path_str,
+                        e.to_string()
+                    ),
+                    Span::unknown(),
+                ),
+            );
+            std::process::exit(1);
+        }
+    };
+
+    engine_state.start_in_file(Some(file_path_str));
+
+    let mut parent = file_path.clone();
+    parent.pop();
+
+    stack.add_env_var(
+        "FILE_PWD".to_string(),
+        Value::string(parent.to_string_lossy(), Span::unknown()),
+    );
 
     let mut working_set = StateWorkingSet::new(engine_state);
-    trace!("parsing file: {}", path);
-
-    let _ = parse(&mut working_set, Some(&path), &file, false, &[]);
+    trace!("parsing file: {}", file_path_str);
+    let _ = parse(&mut working_set, Some(file_path_str), &file, false, &[]);
 
     if working_set.find_decl(b"main", &Type::Any).is_some() {
         let args = format!("main {}", args.join(" "));
 
-        if !eval_source(engine_state, stack, &file, &path, PipelineData::empty()) {
+        if !eval_source(
+            engine_state,
+            stack,
+            &file,
+            file_path_str,
+            PipelineData::empty(),
+        ) {
             std::process::exit(1);
         }
         if !eval_source(engine_state, stack, args.as_bytes(), "<commandline>", input) {
             std::process::exit(1);
         }
-    } else if !eval_source(engine_state, stack, &file, &path, input) {
+    } else if !eval_source(engine_state, stack, &file, file_path_str, input) {
         std::process::exit(1);
     }
 

crates/nu-protocol/src/shell_error.rs

@@ -749,6 +749,15 @@ Either make sure {0} is a string, or add a 'to_string' entry for it in ENV_CONVE
     #[diagnostic(code(nu::parser::non_utf8), url(docsrs))]
     NonUtf8(#[label = "non-UTF8 string"] Span),
 
+    /// The given input must be valid UTF-8 for further processing.
+    ///
+    /// ## Resolution
+    ///
+    /// Check your input's encoding. Are there any funny characters/bytes?
+    #[error("Non-UTF8 string")]
+    #[diagnostic(code(nu::parser::non_utf8_custom), url(docsrs))]
+    NonUtf8Custom(String, #[label = "{0}"] Span),
+
     /// A custom value could not be converted to a Dataframe.
     ///
     /// ## Resolution

tests/shell/environment/env.rs

@@ -118,6 +118,17 @@ fn passes_with_env_env_var_to_external_process() {
     assert_eq!(actual.out, "foo");
 }
 
+#[test]
+fn has_file_pwd() {
+    Playground::setup("has_file_pwd", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContent("spam.nu", "$env.FILE_PWD")]);
+
+        let actual = nu!(cwd: dirs.test(), "nu spam.nu");
+
+        assert!(actual.out.ends_with("has_file_pwd"));
+    })
+}
+
 // FIXME: autoenv not currently implemented
 #[ignore]
 #[test]