From f481879ed389582d9849ba91b56468f14089798d Mon Sep 17 00:00:00 2001
From: Antoine Stevan <44101798+amtoine@users.noreply.github.com>
Date: Tue, 3 Oct 2023 18:57:26 +0200
Subject: [PATCH] make "can't follow stream paths" error a bit better (#10569)
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related to
- https://github.com/nushell/nushell/issues/9373
- https://github.com/nushell/nushell/issues/8639

might be able to close https://github.com/nushell/nushell/issues/8639?

# Description
"can't follow stream paths" errors have always been a bit scary and
obnoxious because they give no information about what happens...

in this PR i try to slightly improve the error message by telling if the
stream was empty or not and give span information when available.

# User-Facing Changes
```nushell
> update value (get value)
Error: nu::shell::incompatible_path_access

  × Data cannot be accessed with a cell path
   ╭─[entry #1:1:1]
 1 │ update value (get value)
   ·               ─┬─
   ·                ╰── empty pipeline doesn't support cell paths
   ╰────
```
```nushell
> ^echo "foo" | get 0
Error: nu::shell::incompatible_path_access

  × Data cannot be accessed with a cell path
   ╭─[entry #2:1:1]
 1 │ ^echo "foo" | get 0
   ·  ──┬─
   ·    ╰── external stream doesn't support cell paths
   ╰────
```

# Tests + Formatting

# After Submitting
---
 crates/nu-protocol/src/pipeline_data.rs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/crates/nu-protocol/src/pipeline_data.rs b/crates/nu-protocol/src/pipeline_data.rs
index f9b1c1220b..cf96eca13e 100644
--- a/crates/nu-protocol/src/pipeline_data.rs
+++ b/crates/nu-protocol/src/pipeline_data.rs
@@ -393,7 +393,14 @@ impl PipelineData {
                 Value::list(stream.collect(), head).follow_cell_path(cell_path, insensitive)
             }
             PipelineData::Value(v, ..) => v.follow_cell_path(cell_path, insensitive),
-            _ => Err(ShellError::IOError("can't follow stream paths".into())),
+            PipelineData::Empty => Err(ShellError::IncompatiblePathAccess {
+                type_name: "empty pipeline".to_string(),
+                span: head,
+            }),
+            PipelineData::ExternalStream { span, .. } => Err(ShellError::IncompatiblePathAccess {
+                type_name: "external stream".to_string(),
+                span,
+            }),
         }
     }