From 9c7b25134b7d0ad96f472387f5bec13f9921f0d1 Mon Sep 17 00:00:00 2001
From: Dietrich Daroch <Dietrich.Daroch@gmail.com>
Date: Sun, 6 Dec 2020 15:19:04 -0300
Subject: [PATCH] Parsing: Explain parsing errors and show sample lines.
 (#2774)
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This makes the errors slightly better. It took me a while to realize I was missing the `--raw` flag.

```
open "data.csv" | from csv --separator ';'
```

    error: Could not parse as CSV split by ',' (Line 1: expected 1 fields, found 14)
      ┌─ shell:1:1
      │
    1 │ open "data.csv" | from csv --separator ';'
      │ ^^^^ ------------------------------------------------- value originates from here
      │ │
      │ input cannot be parsed as CSV split by ','. Sample input:
    Name;Data
    Ugly;row
    AnotherUgly;row

I think this still needs some refinement. Maybe we don't want to show
the separator all the time, omitting the defaults or the separator
on other formats.
---
 crates/nu-cli/src/commands/from_delimited_data.rs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/crates/nu-cli/src/commands/from_delimited_data.rs b/crates/nu-cli/src/commands/from_delimited_data.rs
index 3e2c26730..fb4eb9cfa 100644
--- a/crates/nu-cli/src/commands/from_delimited_data.rs
+++ b/crates/nu-cli/src/commands/from_delimited_data.rs
@@ -54,6 +54,7 @@ pub async fn from_delimited_data(
 ) -> Result<OutputStream, ShellError> {
     let name_tag = name;
     let concat_string = input.collect_string(name_tag.clone()).await?;
+    let sample_lines = concat_string.item.lines().take(3).collect_vec().join("\n");
 
     match from_delimited_string_to_value(concat_string.item, headerless, sep, name_tag.clone()) {
         Ok(x) => match x {
@@ -65,10 +66,16 @@ pub async fn from_delimited_data(
         },
         Err(err) => {
             let line_one = match pretty_csv_error(err) {
-                Some(pretty) => format!("Could not parse as {} ({})", format_name, pretty),
-                None => format!("Could not parse as {}", format_name),
+                Some(pretty) => format!(
+                    "Could not parse as {} split by '{}' ({})",
+                    format_name, sep, pretty
+                ),
+                None => format!("Could not parse as {} split by '{}'", format_name, sep),
             };
-            let line_two = format!("input cannot be parsed as {}", format_name);
+            let line_two = format!(
+                "input cannot be parsed as {} split by '{}'. Input's first lines:\n{}",
+                format_name, sep, sample_lines
+            );
 
             Err(ShellError::labeled_error_with_secondary(
                 line_one,