From eca4f9f195356ded09779c6481566733e280ed09 Mon Sep 17 00:00:00 2001
From: Erik Krieg <erik.c.krieg@gmail.com>
Date: Fri, 26 Aug 2022 00:47:33 -0400
Subject: [PATCH] makes slash operator default lhs value to an empty string

---
 src/parser.rs           | 17 +++++++++++++----
 src/string_kind.rs      |  4 ++--
 tests/slash_operator.rs |  9 +++++++++
 3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/parser.rs b/src/parser.rs
index 00ec7e7edf..d696014c3f 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -405,18 +405,27 @@ impl<'tokens, 'src> Parser<'tokens, 'src> {
     let expression = if self.accepted_keyword(Keyword::If)? {
       self.parse_conditional()?
     } else {
-      let value = self.parse_value()?;
-
+      let value = self.parse_value();
       if self.accepted(Slash)? {
+        // Enables Slash operator to build absolute paths, like `/ "Users"`, by
+        // setting a default empty string on the lhs if the resulting expression
+        // is not Ok.
+        let value = value.unwrap_or(Expression::StringLiteral {
+          string_literal: StringLiteral {
+            kind: StringKind::new(string_kind::StringDelimiter::QuoteDouble, false),
+            raw: "",
+            cooked: "".to_string(),
+          },
+        });
         let lhs = Box::new(value);
         let rhs = Box::new(self.parse_expression()?);
         Expression::Join { lhs, rhs }
       } else if self.accepted(Plus)? {
-        let lhs = Box::new(value);
+        let lhs = Box::new(value?);
         let rhs = Box::new(self.parse_expression()?);
         Expression::Concatenation { lhs, rhs }
       } else {
-        value
+        value?
       }
     };
 
diff --git a/src/string_kind.rs b/src/string_kind.rs
index edfbe46ce3..dbb5496d07 100644
--- a/src/string_kind.rs
+++ b/src/string_kind.rs
@@ -7,7 +7,7 @@ pub(crate) struct StringKind {
 }
 
 #[derive(Debug, PartialEq, Clone, Copy, Ord, PartialOrd, Eq)]
-enum StringDelimiter {
+pub(crate) enum StringDelimiter {
   Backtick,
   QuoteDouble,
   QuoteSingle,
@@ -26,7 +26,7 @@ impl StringKind {
     Self::new(StringDelimiter::QuoteSingle, false),
   ];
 
-  const fn new(delimiter: StringDelimiter, indented: bool) -> Self {
+  pub(crate) const fn new(delimiter: StringDelimiter, indented: bool) -> Self {
     Self {
       delimiter,
       indented,
diff --git a/tests/slash_operator.rs b/tests/slash_operator.rs
index 5995a32e7b..9168fbee1e 100644
--- a/tests/slash_operator.rs
+++ b/tests/slash_operator.rs
@@ -18,6 +18,15 @@ fn twice() {
     .run();
 }
 
+#[test]
+fn no_lhs() {
+  Test::new()
+    .justfile("x := / 'a'")
+    .args(&["--evaluate", "x"])
+    .stdout("/a")
+    .run();
+}
+
 #[test]
 fn default_un_parenthesized() {
   Test::new()