From 3d62528d8ce472db16ffc663fc342b3143f87b09 Mon Sep 17 00:00:00 2001
From: pwygab <88221256+merelymyself@users.noreply.github.com>
Date: Thu, 26 May 2022 08:13:14 +0800
Subject: [PATCH] Makes a more helpful error for `let` in pipeline (#5632)

* a more helpful error for let in pipeline

* a more helpful error for let in pipeline fmt

* changed help message

* type-o

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>
---
 crates/nu-parser/src/errors.rs | 11 +++++++++++
 crates/nu-parser/src/parser.rs |  7 ++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/crates/nu-parser/src/errors.rs b/crates/nu-parser/src/errors.rs
index 4f51d004af..a2ed170d31 100644
--- a/crates/nu-parser/src/errors.rs
+++ b/crates/nu-parser/src/errors.rs
@@ -78,6 +78,16 @@ pub enum ParseError {
     )]
     BuiltinCommandInPipeline(String, #[label("not allowed in pipeline")] Span),
 
+    #[error("Let statement used in pipeline.")]
+    #[diagnostic(
+        code(nu::parser::unexpected_keyword),
+        url(docsrs),
+        help(
+            "Assigning '{0}' to '{1}' does not produce a value to be piped. If the pipeline is meant to apply to '{0}' by itself, use 'let {1} = ({0} | ...)'."
+        )
+    )]
+    LetInPipeline(String, String, #[label("let in pipeline")] Span),
+
     #[error("Incorrect value")]
     #[diagnostic(code(nu::parser::incorrect_value), url(docsrs), help("{2}"))]
     IncorrectValue(String, #[label("unexpected {0}")] Span, String),
@@ -300,6 +310,7 @@ impl ParseError {
             ParseError::ExpectedKeyword(_, s) => *s,
             ParseError::UnexpectedKeyword(_, s) => *s,
             ParseError::BuiltinCommandInPipeline(_, s) => *s,
+            ParseError::LetInPipeline(_, _, s) => *s,
             ParseError::IncorrectValue(_, s, _) => *s,
             ParseError::MultipleRestParams(s) => *s,
             ParseError::VariableNotFound(s) => *s,
diff --git a/crates/nu-parser/src/parser.rs b/crates/nu-parser/src/parser.rs
index c7ec102231..5ecef6cca2 100644
--- a/crates/nu-parser/src/parser.rs
+++ b/crates/nu-parser/src/parser.rs
@@ -4371,7 +4371,12 @@ pub fn parse_expression(
                     expand_aliases_denylist,
                 )
                 .0,
-                Some(ParseError::BuiltinCommandInPipeline("let".into(), spans[0])),
+                Some(ParseError::LetInPipeline(
+                    String::from_utf8_lossy(working_set.get_span_contents(spans[spans.len() - 1]))
+                        .to_string(),
+                    String::from_utf8_lossy(working_set.get_span_contents(spans[1])).to_string(),
+                    spans[0],
+                )),
             ),
             b"alias" => (
                 parse_call(