Add environment variable support for modules (#331)

* Add 'expor env' dummy command

* (WIP) Abstract away module exportables as Overlay

* Switch to Overlays for use/hide

Works for decls only right now.

* Fix passing import patterns of hide to eval

* Simplify use/hide of decls

* Add ImportPattern as Expr; Add use env eval

Still no parsing of "export env" so I can't test it yet.

* Refactor export parsing; Add InternalError

* Add env var export and activation; Misc changes

Now it is possible to `use` env var that was exported from a module.

This commit also adds some new errors and other small changes.

* Add env var hiding

* Fix eval not recognizing hidden decls

Without this change, calling `hide foo`, the evaluator does not know
whether a custom command named "foo" was hidden during parsing,
therefore, it is not possible to reliably throw an error about the "foo"
name not found.

* Add use/hide/export env var tests; Cleanup; Notes

* Ignore hide env related tests for now

* Fix main branch merge mess

* Fixed multi-word export def

* Fix hiding tests on Windows

* Remove env var hiding for now

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

@@ -0,0 +1,41 @@
+use nu_engine::get_full_help;
+use nu_protocol::{
+    ast::Call,
+    engine::{Command, EngineState, Stack},
+    IntoPipelineData, PipelineData, Signature, Value,
+};
+
+#[derive(Clone)]
+pub struct ExportCommand;
+
+impl Command for ExportCommand {
+    fn name(&self) -> &str {
+        "export"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("export")
+    }
+
+    fn usage(&self) -> &str {
+        "Export custom commands or environment variables from a module."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        Ok(Value::String {
+            val: get_full_help(
+                &ExportCommand.signature(),
+                &ExportCommand.examples(),
+                engine_state,
+            ),
+            span: call.head,
+        }
+        .into_pipeline_data())
+    }
+}

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

@@ -16,7 +16,7 @@ impl Command for ExportDef {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("export def")
-            .required("target", SyntaxShape::String, "definition name")
+            .required("name", SyntaxShape::String, "definition name")
             .required("params", SyntaxShape::Signature, "parameters")
             .required(
                 "block",

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

@@ -0,0 +1,41 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{PipelineData, Signature, SyntaxShape};
+
+#[derive(Clone)]
+pub struct ExportEnv;
+
+impl Command for ExportEnv {
+    fn name(&self) -> &str {
+        "export env"
+    }
+
+    fn usage(&self) -> &str {
+        "Export a block from a module that will be evaluated as an environment variable when imported."
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("export env")
+            .required(
+                "name",
+                SyntaxShape::String,
+                "name of the environment variable",
+            )
+            .required(
+                "block",
+                SyntaxShape::Block(Some(vec![])),
+                "body of the environment variable definition",
+            )
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        //TODO: Add the env to stack
+        Ok(PipelineData::new(call.head))
+    }
+}

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

@@ -2,7 +2,9 @@ mod alias;
 mod def;
 mod do_;
 mod echo;
+mod export;
 mod export_def;
+mod export_env;
 mod for_;
 mod help;
 mod hide;
@@ -16,7 +18,9 @@ pub use alias::Alias;
 pub use def::Def;
 pub use do_::Do;
 pub use echo::Echo;
+pub use export::ExportCommand;
 pub use export_def::ExportDef;
+pub use export_env::ExportEnv;
 pub use for_::For;
 pub use help::Help;
 pub use hide::Hide;

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

@@ -1,6 +1,7 @@
-use nu_protocol::ast::Call;
+use nu_engine::eval_block;
+use nu_protocol::ast::{Call, Expr, Expression, ImportPatternMember};
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{PipelineData, Signature, SyntaxShape};
+use nu_protocol::{PipelineData, ShellError, Signature, Span, SyntaxShape};
 
 #[derive(Clone)]
 pub struct Use;
@@ -20,11 +21,85 @@ impl Command for Use {
 
     fn run(
         &self,
-        _engine_state: &EngineState,
-        _stack: &mut Stack,
+        engine_state: &EngineState,
+        stack: &mut Stack,
         call: &Call,
         _input: PipelineData,
-    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+    ) -> Result<PipelineData, ShellError> {
+        let import_pattern = if let Some(Expression {
+            expr: Expr::ImportPattern(pat),
+            ..
+        }) = call.positional.get(0)
+        {
+            pat
+        } else {
+            return Err(ShellError::InternalError(
+                "Got something else than import pattern".into(),
+            ));
+        };
+
+        if let Some(block_id) = engine_state.find_module(&import_pattern.head.name) {
+            let overlay = &engine_state.get_block(block_id).overlay;
+
+            let env_vars_to_use = if import_pattern.members.is_empty() {
+                overlay.env_vars_with_head(&import_pattern.head.name)
+            } else {
+                match &import_pattern.members[0] {
+                    ImportPatternMember::Glob { .. } => overlay.env_vars(),
+                    ImportPatternMember::Name { name, span } => {
+                        let mut output = vec![];
+
+                        if let Some(id) = overlay.get_env_var_id(name) {
+                            output.push((name.clone(), id));
+                        } else if !overlay.has_decl(name) {
+                            return Err(ShellError::EnvVarNotFoundAtRuntime(*span));
+                        }
+
+                        output
+                    }
+                    ImportPatternMember::List { names } => {
+                        let mut output = vec![];
+
+                        for (name, span) in names {
+                            if let Some(id) = overlay.get_env_var_id(name) {
+                                output.push((name.clone(), id));
+                            } else if !overlay.has_decl(name) {
+                                return Err(ShellError::EnvVarNotFoundAtRuntime(*span));
+                            }
+                        }
+
+                        output
+                    }
+                }
+            };
+
+            for (name, block_id) in env_vars_to_use {
+                let name = if let Ok(s) = String::from_utf8(name.clone()) {
+                    s
+                } else {
+                    return Err(ShellError::NonUtf8(import_pattern.head.span));
+                };
+
+                let block = engine_state.get_block(block_id);
+
+                // TODO: Add string conversions (e.g. int to string)
+                // TODO: Later expand env to take all Values
+                let val = if let Ok(s) =
+                    eval_block(engine_state, stack, block, PipelineData::new(call.head))?
+                        .into_value(Span::unknown())
+                        .as_string()
+                {
+                    s
+                } else {
+                    return Err(ShellError::EnvVarNotAString(import_pattern.span()));
+                };
+
+                stack.add_env_var(name, val);
+            }
+        } else {
+            return Err(ShellError::EnvVarNotFoundAtRuntime(call.positional[0].span));
+        }
+
         Ok(PipelineData::new(call.head))
     }
 }

crates/nu-command/src/default_context.rs

@@ -39,7 +39,9 @@ pub fn create_default_context() -> EngineState {
             Do,
             Each,
             Echo,
+            ExportCommand,
             ExportDef,
+            ExportEnv,
             External,
             First,
             For,