From bf19918e3c70a51558e6d975bace0666f780c736 Mon Sep 17 00:00:00 2001
From: JT <jonathan.d.turner@gmail.com>
Date: Mon, 9 Aug 2021 12:19:07 +1200
Subject: [PATCH] begin aliases

---
 src/eval.rs         |  2 ++
 src/main.rs         |  2 +-
 src/parser.rs       | 51 ++++++++++++++++++++++++++++++++++++++++++---
 src/parser_state.rs | 28 +++++++++++++++++++++++++
 4 files changed, 79 insertions(+), 4 deletions(-)

diff --git a/src/eval.rs b/src/eval.rs
index 958256653..20c2b71f9 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -359,6 +359,8 @@ fn eval_call(state: &State, stack: Stack, call: &Call) -> Result<Value, ShellErr
         Ok(Value::Nothing { span: call.head })
     } else if decl.signature.name == "def" {
         Ok(Value::Nothing { span: call.head })
+    } else if decl.signature.name == "alias" {
+        Ok(Value::Nothing { span: call.head })
     } else {
         Err(ShellError::Unsupported(call.head))
     }
diff --git a/src/main.rs b/src/main.rs
index 13a2b029f..90bce1d1a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -43,7 +43,7 @@ fn main() -> std::io::Result<()> {
         working_set.add_decl(sig.into());
 
         let sig = Signature::build("alias")
-            .required("var_name", SyntaxShape::Variable, "variable name")
+            .required("name", SyntaxShape::String, "name of the alias")
             .required(
                 "initial_value",
                 SyntaxShape::Keyword(b"=".to_vec(), Box::new(SyntaxShape::Expression)),
diff --git a/src/parser.rs b/src/parser.rs
index 12e4821af..e8786248c 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -782,13 +782,17 @@ impl<'a> ParserWorkingSet<'a> {
         (Box::new(call), span(spans), error)
     }
 
-    pub fn parse_call(&mut self, spans: &[Span]) -> (Expression, Option<ParseError>) {
+    pub fn parse_call(
+        &mut self,
+        spans: &[Span],
+        expand_aliases: bool,
+    ) -> (Expression, Option<ParseError>) {
         // assume spans.len() > 0?
         let mut pos = 0;
         let mut shorthand = vec![];
 
         while pos < spans.len() {
-            // First, check if there is any environment shorthand
+            // Check if there is any environment shorthand
             let name = self.get_span_contents(spans[pos]);
             let split: Vec<_> = name.splitn(2, |x| *x == b'=').collect();
             if split.len() == 2 {
@@ -807,6 +811,21 @@ impl<'a> ParserWorkingSet<'a> {
         }
 
         let name = self.get_span_contents(spans[pos]);
+
+        if expand_aliases {
+            if let Some(expansion) = self.find_alias(name) {
+                //let mut spans = spans.to_vec();
+                let mut new_spans: Vec<Span> = vec![];
+                new_spans.extend(&spans[0..pos]);
+                new_spans.extend(expansion);
+                if spans.len() > pos {
+                    new_spans.extend(&spans[(pos + 1)..]);
+                }
+
+                return self.parse_call(&new_spans, false);
+            }
+        }
+
         pos += 1;
 
         if let Some(mut decl_id) = self.find_decl(name) {
@@ -2115,7 +2134,7 @@ impl<'a> ParserWorkingSet<'a> {
         match bytes[0] {
             b'0' | b'1' | b'2' | b'3' | b'4' | b'5' | b'6' | b'7' | b'8' | b'9' | b'(' | b'{'
             | b'[' | b'$' | b'"' | b'\'' => self.parse_math_expression(spans),
-            _ => self.parse_call(spans),
+            _ => self.parse_call(spans, true),
         }
     }
 
@@ -2234,6 +2253,30 @@ impl<'a> ParserWorkingSet<'a> {
         }
     }
 
+    pub fn parse_alias(&mut self, spans: &[Span]) -> (Statement, Option<ParseError>) {
+        let name = self.get_span_contents(spans[0]);
+
+        if name == b"alias" && spans.len() >= 4 {
+            let alias_name = self.get_span_contents(spans[1]).to_vec();
+            let _equals = self.get_span_contents(spans[2]);
+
+            let replacement = spans[3..].to_vec();
+
+            self.add_alias(alias_name, replacement);
+        }
+        (
+            Statement::Expression(Expression {
+                expr: Expr::Garbage,
+                span: span(spans),
+                ty: Type::Unknown,
+            }),
+            Some(ParseError::UnknownState(
+                "internal error: let statement unparseable".into(),
+                span(spans),
+            )),
+        )
+    }
+
     pub fn parse_let(&mut self, spans: &[Span]) -> (Statement, Option<ParseError>) {
         let name = self.get_span_contents(spans[0]);
 
@@ -2271,6 +2314,8 @@ impl<'a> ParserWorkingSet<'a> {
             (decl, None)
         } else if let (stmt, None) = self.parse_let(spans) {
             (stmt, None)
+        } else if let (stmt, None) = self.parse_alias(spans) {
+            (stmt, None)
         } else {
             let (expr, err) = self.parse_expression(spans);
             (Statement::Expression(expr), err)
diff --git a/src/parser_state.rs b/src/parser_state.rs
index c53c8f350..db5d721e5 100644
--- a/src/parser_state.rs
+++ b/src/parser_state.rs
@@ -36,6 +36,7 @@ pub type BlockId = usize;
 struct ScopeFrame {
     vars: HashMap<Vec<u8>, VarId>,
     decls: HashMap<Vec<u8>, DeclId>,
+    aliases: HashMap<Vec<u8>, Vec<Span>>,
 }
 
 impl ScopeFrame {
@@ -43,6 +44,7 @@ impl ScopeFrame {
         Self {
             vars: HashMap::new(),
             decls: HashMap::new(),
+            aliases: HashMap::new(),
         }
     }
 }
@@ -352,6 +354,22 @@ impl<'a> ParserWorkingSet<'a> {
         None
     }
 
+    pub fn find_alias(&self, name: &[u8]) -> Option<&[Span]> {
+        for scope in self.delta.scope.iter().rev() {
+            if let Some(spans) = scope.aliases.get(name) {
+                return Some(spans);
+            }
+        }
+
+        for scope in self.permanent_state.scope.iter().rev() {
+            if let Some(spans) = scope.aliases.get(name) {
+                return Some(spans);
+            }
+        }
+
+        None
+    }
+
     pub fn add_variable(&mut self, mut name: Vec<u8>, ty: Type) -> VarId {
         let next_id = self.next_var_id();
 
@@ -373,6 +391,16 @@ impl<'a> ParserWorkingSet<'a> {
         next_id
     }
 
+    pub fn add_alias(&mut self, name: Vec<u8>, replacement: Vec<Span>) {
+        let last = self
+            .delta
+            .scope
+            .last_mut()
+            .expect("internal error: missing stack frame");
+
+        last.aliases.insert(name, replacement);
+    }
+
     pub fn set_variable_type(&mut self, var_id: VarId, ty: Type) {
         let num_permanent_vars = self.permanent_state.num_vars();
         if var_id < num_permanent_vars {