Evaluate string interpolation at parse time (#11562)

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Closes #11561

# Description
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This PR will allow string interpolation at parse time.

Since the actual config hasn't been loaded at parse time, this uses the
`get_config()` method on `StateWorkingSet`. So file sizes and datetimes
(I think those are the only things whose string representations depend
on the config) may be formatted differently from how users have
configured things, which may come as a surprise to some. It does seem
unlikely that anyone would be formatting file sizes or date times at
parse time. Still, something to think about if/before this PR merged.

Also, I changed the `ModuleNotFound` error to include the name of the
module.

# User-Facing Changes
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helps us keep track of breaking changes. -->

Users will be able to do stuff like:

```nu
const x = [1 2 3]
const y = $"foo($x)" // foo[1, 2, 3]
```

The main use case is `use`-ing and `source`-ing files at parse time:

```nu
const file = "foo.nu"
use $"($file)"
```

If the module isn't found, you'll see an error like this:
```
Error: nu::parser::module_not_found

  × Module not found.
   ╭─[entry #3:1:1]
 1 │  use $"($file)"
   ·      ─────┬────
   ·           ╰── module foo.nu not found
   ╰────
  help: module files and their paths must be available before your script is run as parsing occurs before anything is evaluated
```

# Tests + Formatting
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crates/nu-std"` to run the tests for the standard library

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# After Submitting
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Although there's user-facing changes, there's probably no need to change
the docs since people probably already expect string interpolation to
work at parse time.

Edit: @kubouch pointed out that we'd need to document the fact that
stuff like file sizes and datetimes won't get formatted according to
user's runtime configs, so I'll make a PR to nushell.github.io after
this one

crates/nu-engine/src/eval.rs

@@ -1,4 +1,4 @@
-use crate::{current_dir_str, get_full_help};
+use crate::{current_dir_str, get_config, get_full_help};
 use nu_path::expand_path_with;
 use nu_protocol::{
     ast::{
@@ -7,11 +7,11 @@ use nu_protocol::{
     },
     engine::{Closure, EngineState, Stack},
     eval_base::Eval,
-    DeclId, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError, Span,
-    Spanned, Type, Value, VarId, ENV_VARIABLE_ID,
+    Config, DeclId, IntoPipelineData, PipelineData, ShellError, Span, Spanned, Type, Value, VarId,
+    ENV_VARIABLE_ID,
 };
-use std::collections::HashMap;
 use std::thread::{self, JoinHandle};
+use std::{borrow::Cow, collections::HashMap};
 
 pub fn eval_call(
     engine_state: &EngineState,
@@ -913,9 +913,13 @@ impl Eval for EvalRuntime {
 
     type MutState = Stack;
 
+    fn get_config<'a>(engine_state: Self::State<'a>, stack: &mut Stack) -> Cow<'a, Config> {
+        Cow::Owned(get_config(engine_state, stack))
+    }
+
     fn eval_filepath(
-        engine_state: Self::State<'_>,
-        stack: &mut Self::MutState,
+        engine_state: &EngineState,
+        stack: &mut Stack,
         path: String,
         quoted: bool,
         span: Span,
@@ -1141,26 +1145,6 @@ impl Eval for EvalRuntime {
         Ok(Value::closure(Closure { block_id, captures }, span))
     }
 
-    fn eval_string_interpolation(
-        engine_state: &EngineState,
-        stack: &mut Stack,
-        exprs: &[Expression],
-        span: Span,
-    ) -> Result<Value, ShellError> {
-        let mut parts = vec![];
-        for expr in exprs {
-            parts.push(eval_expression(engine_state, stack, expr)?);
-        }
-
-        let config = engine_state.get_config();
-
-        parts
-            .into_iter()
-            .into_pipeline_data(None)
-            .collect_string("", config)
-            .map(|x| Value::string(x, span))
-    }
-
     fn eval_overlay(engine_state: &EngineState, span: Span) -> Result<Value, ShellError> {
         let name = String::from_utf8_lossy(engine_state.get_span_contents(span)).to_string();
 

crates/nu-parser/src/parse_keywords.rs

@@ -1969,14 +1969,20 @@ fn parse_module_file(
     } else if let Some(stem) = path.file_stem() {
         stem.to_string_lossy().to_string()
     } else {
-        working_set.error(ParseError::ModuleNotFound(path_span));
+        working_set.error(ParseError::ModuleNotFound(
+            path_span,
+            path.path().to_string_lossy().to_string(),
+        ));
         return None;
     };
 
     let contents = if let Some(contents) = path.read(working_set) {
         contents
     } else {
-        working_set.error(ParseError::ModuleNotFound(path_span));
+        working_set.error(ParseError::ModuleNotFound(
+            path_span,
+            path.path().to_string_lossy().to_string(),
+        ));
         return None;
     };
 
@@ -2031,20 +2037,26 @@ pub fn parse_module_file_or_dir(
         if let Some(path) = find_in_dirs(&module_path_str, working_set, &cwd, LIB_DIRS_VAR) {
             path
         } else {
-            working_set.error(ParseError::ModuleNotFound(path_span));
+            working_set.error(ParseError::ModuleNotFound(path_span, module_path_str));
             return None;
         };
 
     if module_path.is_dir() {
         if module_path.read_dir().is_none() {
-            working_set.error(ParseError::ModuleNotFound(path_span));
+            working_set.error(ParseError::ModuleNotFound(
+                path_span,
+                module_path.path().to_string_lossy().to_string(),
+            ));
             return None;
         };
 
         let module_name = if let Some(stem) = module_path.file_stem() {
             stem.to_string_lossy().to_string()
         } else {
-            working_set.error(ParseError::ModuleNotFound(path_span));
+            working_set.error(ParseError::ModuleNotFound(
+                path_span,
+                module_path.path().to_string_lossy().to_string(),
+            ));
             return None;
         };
 
@@ -2084,7 +2096,10 @@ pub fn parse_module_file_or_dir(
     } else if module_path.is_file() {
         parse_module_file(working_set, module_path, path_span, name_override)
     } else {
-        working_set.error(ParseError::ModuleNotFound(path_span));
+        working_set.error(ParseError::ModuleNotFound(
+            path_span,
+            module_path.path().to_string_lossy().to_string(),
+        ));
         None
     }
 }
@@ -2200,7 +2215,10 @@ pub fn parse_module(
         ) {
             return (pipeline, Some(module_id));
         } else {
-            working_set.error(ParseError::ModuleNotFound(module_name_or_path_span));
+            working_set.error(ParseError::ModuleNotFound(
+                module_name_or_path_span,
+                module_name_or_path,
+            ));
             return (pipeline, None);
         }
     }
@@ -2397,7 +2415,10 @@ pub fn parse_use(working_set: &mut StateWorkingSet, spans: &[Span]) -> (Pipeline
             module_id,
         )
     } else {
-        working_set.error(ParseError::ModuleNotFound(import_pattern.head.span));
+        working_set.error(ParseError::ModuleNotFound(
+            import_pattern.head.span,
+            String::from_utf8_lossy(&import_pattern.head.name).to_string(),
+        ));
         return (
             Pipeline::from_vec(vec![Expression {
                 expr: Expr::Call(call),
@@ -2567,7 +2588,10 @@ pub fn parse_hide(working_set: &mut StateWorkingSet, spans: &[Span]) -> Pipeline
                     (false, Module::new(b"tmp".to_vec()))
                 }
             } else {
-                working_set.error(ParseError::ModuleNotFound(spans[1]));
+                working_set.error(ParseError::ModuleNotFound(
+                    spans[1],
+                    String::from_utf8_lossy(&import_pattern.head.name).to_string(),
+                ));
                 return garbage_pipeline(spans);
             };
 

crates/nu-protocol/src/eval_base.rs

@@ -3,9 +3,9 @@ use crate::{
         eval_operator, Assignment, Bits, Boolean, Call, Comparison, Expr, Expression,
         ExternalArgument, Math, Operator, RecordItem,
     },
-    Range, Record, ShellError, Span, Value, VarId,
+    Config, IntoInterruptiblePipelineData, Range, Record, ShellError, Span, Value, VarId,
 };
-use std::collections::HashMap;
+use std::{borrow::Cow, collections::HashMap};
 
 /// To share implementations for regular eval and const eval
 pub trait Eval {
@@ -271,7 +271,18 @@ pub trait Eval {
                 Self::eval_row_condition_or_closure(state, mut_state, *block_id, expr.span)
             }
             Expr::StringInterpolation(exprs) => {
-                Self::eval_string_interpolation(state, mut_state, exprs, expr.span)
+                let mut parts = vec![];
+                for expr in exprs {
+                    parts.push(Self::eval(state, mut_state, expr)?);
+                }
+
+                let config = Self::get_config(state, mut_state);
+
+                parts
+                    .into_iter()
+                    .into_pipeline_data(None)
+                    .collect_string("", &config)
+                    .map(|x| Value::string(x, expr.span))
             }
             Expr::Overlay(_) => Self::eval_overlay(state, expr.span),
             Expr::GlobPattern(pattern, quoted) => {
@@ -294,6 +305,8 @@ pub trait Eval {
         }
     }
 
+    fn get_config<'a>(state: Self::State<'a>, mut_state: &mut Self::MutState) -> Cow<'a, Config>;
+
     fn eval_filepath(
         state: Self::State<'_>,
         mut_state: &mut Self::MutState,
@@ -366,13 +379,6 @@ pub trait Eval {
         span: Span,
     ) -> Result<Value, ShellError>;
 
-    fn eval_string_interpolation(
-        state: Self::State<'_>,
-        mut_state: &mut Self::MutState,
-        exprs: &[Expression],
-        span: Span,
-    ) -> Result<Value, ShellError>;
-
     fn eval_overlay(state: Self::State<'_>, span: Span) -> Result<Value, ShellError>;
 
     fn eval_glob_pattern(

crates/nu-protocol/src/eval_const.rs

@@ -2,10 +2,13 @@ use crate::{
     ast::{Assignment, Block, Call, Expr, Expression, ExternalArgument, PipelineElement},
     engine::{EngineState, StateWorkingSet},
     eval_base::Eval,
-    record, HistoryFileFormat, PipelineData, Record, ShellError, Span, Value, VarId,
+    record, Config, HistoryFileFormat, PipelineData, Record, ShellError, Span, Value, VarId,
 };
 use nu_system::os_info::{get_kernel_version, get_os_arch, get_os_family, get_os_name};
-use std::path::{Path, PathBuf};
+use std::{
+    borrow::Cow,
+    path::{Path, PathBuf},
+};
 
 pub fn create_nu_constant(engine_state: &EngineState, span: Span) -> Result<Value, ShellError> {
     fn canonicalize_path(engine_state: &EngineState, path: &Path) -> PathBuf {
@@ -278,6 +281,10 @@ impl Eval for EvalConst {
 
     type MutState = ();
 
+    fn get_config<'a>(state: Self::State<'a>, _: &mut ()) -> Cow<'a, Config> {
+        Cow::Borrowed(state.get_config())
+    }
+
     fn eval_filepath(
         _: &StateWorkingSet,
         _: &mut (),
@@ -377,15 +384,6 @@ impl Eval for EvalConst {
         Err(ShellError::NotAConstant { span })
     }
 
-    fn eval_string_interpolation(
-        _: &StateWorkingSet,
-        _: &mut (),
-        _: &[Expression],
-        span: Span,
-    ) -> Result<Value, ShellError> {
-        Err(ShellError::NotAConstant { span })
-    }
-
     fn eval_overlay(_: &StateWorkingSet, span: Span) -> Result<Value, ShellError> {
         Err(ShellError::NotAConstant { span })
     }

crates/nu-protocol/src/parse_error.rs

@@ -207,7 +207,7 @@ pub enum ParseError {
         code(nu::parser::module_not_found),
         help("module files and their paths must be available before your script is run as parsing occurs before anything is evaluated")
     )]
-    ModuleNotFound(#[label = "module not found"] Span),
+    ModuleNotFound(#[label = "module {1} not found"] Span, String),
 
     #[error("Missing mod.nu file.")]
     #[diagnostic(
@@ -520,7 +520,7 @@ impl ParseError {
             ParseError::VariableNotValid(s) => *s,
             ParseError::AliasNotValid(s) => *s,
             ParseError::CommandDefNotValid(s) => *s,
-            ParseError::ModuleNotFound(s) => *s,
+            ParseError::ModuleNotFound(s, _) => *s,
             ParseError::ModuleMissingModNuFile(_, s) => *s,
             ParseError::NamedAsModule(_, _, _, s) => *s,
             ParseError::ModuleDoubleMain(_, s) => *s,

tests/const_/mod.rs

@@ -108,6 +108,19 @@ fn const_string() {
     assert_eq!(actual.out, "abc");
 }
 
+#[test]
+fn const_string_interpolation() {
+    let actual = nu!(r#"
+        const x = 2
+        const s = $"var: ($x), date: (2021-02-27T13:55:40+00:00), file size: (2kb)"
+        $s
+    "#);
+    assert_eq!(
+        actual.out,
+        "var: 2, date: Sat, 27 Feb 2021 13:55:40 +0000 (2 years ago), file size: 2.0 KiB"
+    );
+}
+
 #[test]
 fn const_nothing() {
     let inp = &["const x = null", "$x | describe"];

tests/modules/mod.rs

@@ -357,7 +357,7 @@ fn module_cyclical_imports_0() {
 
         let actual = nu!(cwd: dirs.test(), &inp.join("; "));
 
-        assert!(actual.err.contains("module not found"));
+        assert!(actual.err.contains("Module not found"));
     })
 }