feat(env): introduce dynamic variables (#360)

Implements infra for dynamic shell values backed by code.

Adds well-known variables: BASHOPTS, BASHPID, BASH_ALIASES, BASH_ARGV0, BASH_CMDS, BASH_SUBSHELL, DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, GROUPS, HOSTNAME, HOSTTYPE, LINENO, MACHTYPE, PIPESTATUS, PPID, SECONDS, SHELLOPTS, SHLVL, SRANDOM, PS4, UID

README.md

@@ -64,7 +64,7 @@ If you feel so inclined, we'd love contributions toward any of the above, with b
 
 ## Testing strategy
 
-This project is primarily tested by comparing its behavior with other existing shells, leveraging the latter as test oracles. The integration tests implemented in this repo include [525+ test cases](brush-shell/tests/cases) run on both this shell and an oracle, comparing standard output and exit codes.
+This project is primarily tested by comparing its behavior with other existing shells, leveraging the latter as test oracles. The integration tests implemented in this repo include [550+ test cases](brush-shell/tests/cases) run on both this shell and an oracle, comparing standard output and exit codes.
 
 For more details, please consult the [reference documentation on integration testing](docs/reference/integration-testing.md).
 

brush-core/src/arithmetic.rs

@@ -141,17 +141,19 @@ impl Evaluatable for ast::ArithmeticExpr {
 
 fn deref_lvalue(shell: &mut Shell, lvalue: &ast::ArithmeticTarget) -> Result<i64, EvalError> {
     let value_str: Cow<'_, str> = match lvalue {
-        ast::ArithmeticTarget::Variable(name) => shell
-            .env
-            .get(name)
-            .map_or_else(|| Cow::Borrowed(""), |(_, v)| v.value().to_cow_string()),
+        ast::ArithmeticTarget::Variable(name) => {
+            shell.get_env_str(name).unwrap_or(Cow::Borrowed(""))
+        }
         ast::ArithmeticTarget::ArrayElement(name, index_expr) => {
             let index_str = index_expr.eval(shell)?.to_string();
 
             shell
                 .env
                 .get(name)
-                .map_or_else(|| Ok(None), |(_, v)| v.value().get_at(index_str.as_str()))
+                .map_or_else(
+                    || Ok(None),
+                    |(_, v)| v.value().get_at(index_str.as_str(), shell),
+                )
                 .map_err(|_err| EvalError::FailedToAccessArray)?
                 .unwrap_or(Cow::Borrowed(""))
         }

brush-core/src/builtins/cd.rs

@@ -49,7 +49,7 @@ impl builtins::Command for CdCommand {
             // `cd -', equivalent to `cd $OLDPWD'
             if target_dir.as_os_str() == "-" {
                 should_print = true;
-                if let Some(oldpwd) = context.shell.env.get_str("OLDPWD") {
+                if let Some(oldpwd) = context.shell.get_env_str("OLDPWD") {
                     PathBuf::from(oldpwd.to_string())
                 } else {
                     writeln!(context.stderr(), "OLDPWD not set")?;
@@ -61,7 +61,7 @@ impl builtins::Command for CdCommand {
             }
         // `cd' without arguments is equivalent to `cd $HOME'
         } else {
-            if let Some(home_var) = context.shell.env.get_str("HOME") {
+            if let Some(home_var) = context.shell.get_env_str("HOME") {
                 PathBuf::from(home_var.to_string())
             } else {
                 writeln!(context.stderr(), "HOME not set")?;

brush-core/src/builtins/declare.rs

@@ -203,7 +203,7 @@ impl DeclareCommand {
                 Ok(false)
             }
         } else if let Some(variable) = context.shell.env.get_using_policy(name, lookup) {
-            let mut cs = variable.get_attribute_flags();
+            let mut cs = variable.get_attribute_flags(context.shell);
             if cs.is_empty() {
                 cs.push('-');
             }
@@ -219,7 +219,7 @@ impl DeclareCommand {
                 "declare -{cs} {name}{separator_str}{}",
                 variable
                     .value()
-                    .format(variables::FormatStyle::DeclarePrint)?
+                    .format(variables::FormatStyle::DeclarePrint, context.shell)?
             )?;
 
             Ok(true)
@@ -467,7 +467,7 @@ impl DeclareCommand {
             .sorted_by_key(|v| v.0)
         {
             if self.print {
-                let mut cs = variable.get_attribute_flags();
+                let mut cs = variable.get_attribute_flags(context.shell);
                 if cs.is_empty() {
                     cs.push('-');
                 }
@@ -483,13 +483,15 @@ impl DeclareCommand {
                     "declare -{cs} {name}{separator_str}{}",
                     variable
                         .value()
-                        .format(variables::FormatStyle::DeclarePrint)?
+                        .format(variables::FormatStyle::DeclarePrint, context.shell)?
                 )?;
             } else {
                 writeln!(
                     context.stdout(),
                     "{name}={}",
-                    variable.value().format(variables::FormatStyle::Basic)?
+                    variable
+                        .value()
+                        .format(variables::FormatStyle::Basic, context.shell)?
                 )?;
             }
         }

brush-core/src/builtins/export.rs

@@ -98,7 +98,7 @@ impl builtins::Command for ExportCommand {
                         context.stdout(),
                         "declare -x {}=\"{}\"",
                         name,
-                        variable.value().to_cow_string()
+                        variable.value().to_cow_str(context.shell)
                     )?;
                 }
             }

brush-core/src/builtins/getopts.rs

@@ -67,8 +67,7 @@ impl builtins::Command for GetOptsCommand {
         // If unset, assume OPTIND is 1.
         let mut next_index: usize = context
             .shell
-            .env
-            .get_str("OPTIND")
+            .get_env_str("OPTIND")
             .unwrap_or(Cow::Borrowed("1"))
             .parse()?;
 
@@ -92,8 +91,7 @@ impl builtins::Command for GetOptsCommand {
                 const DEFAULT_NEXT_CHAR_INDEX: usize = 1;
                 let next_char_index = context
                     .shell
-                    .env
-                    .get_str(VAR_GETOPTS_NEXT_CHAR_INDEX)
+                    .get_env_str(VAR_GETOPTS_NEXT_CHAR_INDEX)
                     .map_or(DEFAULT_NEXT_CHAR_INDEX, |s| {
                         s.parse().unwrap_or(DEFAULT_NEXT_CHAR_INDEX)
                     });

brush-core/src/builtins/set.rs

@@ -400,7 +400,8 @@ fn display_all(context: &commands::ExecutionContext<'_>) -> Result<(), error::Er
         writeln!(
             context.stdout(),
             "{name}={}",
-            var.value().format(variables::FormatStyle::Basic)?,
+            var.value()
+                .format(variables::FormatStyle::Basic, context.shell)?,
         )?;
     }
 

brush-core/src/commands.rs

@@ -226,7 +226,7 @@ pub(crate) fn compose_std_command<S: AsRef<OsStr>>(
     if !empty_env {
         for (name, var) in shell.env.iter() {
             if var.is_exported() {
-                let value_as_str = var.value().to_cow_string();
+                let value_as_str = var.value().to_cow_str(shell);
                 cmd.env(name, value_as_str.as_ref());
             }
         }

brush-core/src/env.rs

@@ -2,6 +2,7 @@ use std::borrow::Cow;
 use std::collections::HashMap;
 
 use crate::error;
+use crate::shell;
 use crate::variables::{self, ShellValue, ShellValueUnsetType, ShellVariable};
 
 /// Represents the policy for looking up variables in a shell environment.
@@ -179,9 +180,10 @@ impl ShellEnvironment {
     /// # Arguments
     ///
     /// * `name` - The name of the variable to retrieve.
-    pub fn get_str<S: AsRef<str>>(&self, name: S) -> Option<Cow<'_, str>> {
+    /// * `shell` - The shell owning the environment.
+    pub fn get_str<S: AsRef<str>>(&self, name: S, shell: &shell::Shell) -> Option<Cow<'_, str>> {
         self.get(name.as_ref())
-            .map(|(_, v)| v.value().to_cow_string())
+            .map(|(_, v)| v.value().to_cow_str(shell))
     }
 
     /// Checks if a variable of the given name is set in the environment.

brush-core/src/expansion.rs

@@ -949,7 +949,7 @@ impl<'a> WordExpander<'a> {
                     .try_resolve_parameter_to_variable(&parameter, indirect)
                     .await?
                 {
-                    Ok(var.get_attribute_flags().into())
+                    Ok(var.get_attribute_flags(self.shell).into())
                 } else {
                     Ok(String::new().into())
                 }
@@ -963,17 +963,19 @@ impl<'a> WordExpander<'a> {
                     .try_resolve_parameter_to_variable(&parameter, indirect)
                     .await?
                 {
-                    let assignable_value_str = var.value().to_assignable_str(index.as_deref());
+                    let assignable_value_str =
+                        var.value().to_assignable_str(index.as_deref(), self.shell);
 
-                    let mut attr_str = var.get_attribute_flags();
+                    let mut attr_str = var.get_attribute_flags(self.shell);
                     if attr_str.is_empty() {
                         attr_str.push('-');
                     }
 
                     match var.value() {
                         ShellValue::IndexedArray(_)
                         | ShellValue::AssociativeArray(_)
-                        | ShellValue::Random => {
+                        // TODO(dynamic): confirm this
+                        | ShellValue::Dynamic { .. } => {
                             let equals_or_nothing = if assignable_value_str.is_empty() {
                                 ""
                             } else {
@@ -1120,7 +1122,7 @@ impl<'a> WordExpander<'a> {
                 concatenate,
             } => {
                 let keys = if let Some((_, var)) = self.shell.env.get(variable_name) {
-                    var.value().get_element_keys()
+                    var.value().get_element_keys(self.shell)
                 } else {
                     vec![]
                 };
@@ -1273,7 +1275,9 @@ impl<'a> WordExpander<'a> {
                     if matches!(var.value(), ShellValue::Unset(_)) {
                         Ok(Expansion::undefined())
                     } else {
-                        Ok(Expansion::from(var.value().to_cow_string().to_string()))
+                        Ok(Expansion::from(
+                            var.value().to_cow_str(self.shell).to_string(),
+                        ))
                     }
                 } else {
                     Ok(Expansion::undefined())
@@ -1298,7 +1302,7 @@ impl<'a> WordExpander<'a> {
 
                 // Index into the array.
                 if let Some((_, var)) = self.shell.env.get(name) {
-                    if let Some(value) = var.value().get_at(index_to_use.as_str())? {
+                    if let Some(value) = var.value().get_at(index_to_use.as_str(), self.shell)? {
                         Ok(Expansion::from(value.to_string()))
                     } else {
                         Ok(Expansion::undefined())
@@ -1309,7 +1313,7 @@ impl<'a> WordExpander<'a> {
             }
             brush_parser::word::Parameter::NamedWithAllIndices { name, concatenate } => {
                 if let Some((_, var)) = self.shell.env.get(name) {
-                    let values = var.value().get_element_values();
+                    let values = var.value().get_element_values(self.shell);
 
                     Ok(Expansion {
                         fields: values
@@ -1374,7 +1378,7 @@ impl<'a> WordExpander<'a> {
                 Ok(Expansion::from(self.shell.last_exit_status.to_string()))
             }
             brush_parser::word::SpecialParameter::CurrentOptionFlags => {
-                Ok(Expansion::from(self.shell.current_option_flags()))
+                Ok(Expansion::from(self.shell.options.get_option_flags()))
             }
             brush_parser::word::SpecialParameter::ProcessId => {
                 Ok(Expansion::from(std::process::id().to_string()))