From 50c2c38727760d44355a4c13928a02996670ddae Mon Sep 17 00:00:00 2001
From: WATANABE Yuki <magicant@wonderwand.net>
Date: Mon, 6 May 2024 23:21:14 +0900
Subject: [PATCH] Reorder simple command words in display

---
 yash-syntax/CHANGELOG.md  |  3 +++
 yash-syntax/src/syntax.rs | 35 +++++++++++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/yash-syntax/CHANGELOG.md b/yash-syntax/CHANGELOG.md
index 12792203..ae9023eb 100644
--- a/yash-syntax/CHANGELOG.md
+++ b/yash-syntax/CHANGELOG.md
@@ -18,6 +18,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   is not followed by any name characters. Previously, it returned
   `Err(SyntaxError::UnclosedParam{…})` if `{` was followed by a non-name
   character other than `}`.
+- `impl std::fmt::Display for SimpleCommand` now prints the command words
+  after the redirections if there are no assignments and the first word looks
+  like a keyword.
 
 ### Fixed
 
diff --git a/yash-syntax/src/syntax.rs b/yash-syntax/src/syntax.rs
index 0e5f29ec..de2c5ae5 100644
--- a/yash-syntax/src/syntax.rs
+++ b/yash-syntax/src/syntax.rs
@@ -73,6 +73,7 @@
 //! here-document contents omitted. To pretty-format an AST in multiple lines
 //! with here-document contents included, you can use ... TODO TBD.
 
+use crate::parser::lex::Keyword;
 use crate::parser::lex::Operator;
 use crate::parser::lex::TryFromOperatorError;
 use crate::source::Location;
@@ -964,6 +965,18 @@ impl SimpleCommand {
     pub fn is_one_word(&self) -> bool {
         self.assigns.is_empty() && self.words.len() == 1 && self.redirs.is_empty()
     }
+
+    /// Tests whether the first word of the simple command is a keyword.
+    #[must_use]
+    fn first_word_is_keyword(&self) -> bool {
+        let Some(word) = self.words.first() else {
+            return false;
+        };
+        let Some(literal) = word.to_string_if_literal() else {
+            return false;
+        };
+        literal.parse::<Keyword>().is_ok()
+    }
 }
 
 impl fmt::Display for SimpleCommand {
@@ -971,8 +984,16 @@ impl fmt::Display for SimpleCommand {
         let i1 = self.assigns.iter().map(|x| x as &dyn fmt::Display);
         let i2 = self.words.iter().map(|x| x as &dyn fmt::Display);
         let i3 = self.redirs.iter().map(|x| x as &dyn fmt::Display);
-        write!(f, "{}", i1.chain(i2).chain(i3).format(" "))
-        // TODO Avoid printing a keyword as the first word
+
+        if !self.assigns.is_empty() || !self.first_word_is_keyword() {
+            write!(f, "{}", i1.chain(i2).chain(i3).format(" "))
+        } else {
+            // If the simple command starts with an assignment or redirection,
+            // the first word may be a keyword which is treated as a plain word.
+            // In this case, we need to avoid the word being interpreted as a
+            // keyword by printing the assignment or redirection first.
+            write!(f, "{}", i3.chain(i2).format(" "))
+        }
     }
 }
 
@@ -1925,6 +1946,16 @@ mod tests {
         assert_eq!(command.to_string(), "foo=bar <<END 1<<-here");
     }
 
+    #[test]
+    fn simple_command_display_with_keyword() {
+        let command = SimpleCommand {
+            assigns: vec![],
+            words: vec!["if".parse().unwrap()],
+            redirs: vec!["<foo".parse().unwrap()].into(),
+        };
+        assert_eq!(command.to_string(), "<foo if");
+    }
+
     #[test]
     fn elif_then_display() {
         let condition: List = "c 1& c 2".parse().unwrap();