Use anyhow more idiomatically (#31052)

https://github.com/zed-industries/zed/issues/30972 brought up another
case where our context is not enough to track the actual source of the
issue: we get a general top-level error without inner error.

The reason for this was `.ok_or_else(|| anyhow!("failed to read HEAD
SHA"))?; ` on the top level.

The PR finally reworks the way we use anyhow to reduce such issues (or
at least make it simpler to bubble them up later in a fix).
On top of that, uses a few more anyhow methods for better readability.

* `.ok_or_else(|| anyhow!("..."))`, `map_err` and other similar error
conversion/option reporting cases are replaced with `context` and
`with_context` calls
* in addition to that, various `anyhow!("failed to do ...")` are
stripped with `.context("Doing ...")` messages instead to remove the
parasitic `failed to` text
* `anyhow::ensure!` is used instead of `if ... { return Err(...); }`
calls
* `anyhow::bail!` is used instead of `return Err(anyhow!(...));`

Release Notes:

- N/A

crates/semantic_index/src/embedding_index.rs

@@ -3,7 +3,7 @@ use crate::{
     embedding::{Embedding, EmbeddingProvider, TextToEmbed},
     indexing::{IndexingEntryHandle, IndexingEntrySet},
 };
-use anyhow::{Context as _, Result, anyhow};
+use anyhow::{Context as _, Result};
 use collections::Bound;
 use feature_flags::FeatureFlagAppExt;
 use fs::Fs;
@@ -422,7 +422,7 @@ impl EmbeddingIndex {
                 .context("failed to create read transaction")?;
             Ok(db
                 .get(&tx, &db_key_for_path(&path))?
-                .ok_or_else(|| anyhow!("no such path"))?
+                .context("no such path")?
                 .chunks
                 .clone())
         })

crates/semantic_index/src/project_index.rs

@@ -282,11 +282,10 @@ impl ProjectIndex {
                 .collect();
 
             let query_embeddings = embedding_provider.embed(&queries[..]).await?;
-            if query_embeddings.len() != queries.len() {
-                return Err(anyhow!(
-                    "The number of query embeddings does not match the number of queries"
-                ));
-            }
+            anyhow::ensure!(
+                query_embeddings.len() == queries.len(),
+                "The number of query embeddings does not match the number of queries"
+            );
 
             let mut results_by_worker = Vec::new();
             for _ in 0..cx.background_executor().num_cpus() {

crates/semantic_index/src/semantic_index.rs

@@ -264,7 +264,6 @@ impl Drop for SemanticDb {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use anyhow::anyhow;
     use chunking::Chunk;
     use embedding_index::{ChunkedFile, EmbeddingIndex};
     use feature_flags::FeatureFlagAppExt;
@@ -446,15 +445,15 @@ mod tests {
         cx.executor().allow_parking();
 
         let provider = Arc::new(TestEmbeddingProvider::new(3, |text| {
-            if text.contains('g') {
-                Err(anyhow!("cannot embed text containing a 'g' character"))
-            } else {
-                Ok(Embedding::new(
-                    ('a'..='z')
-                        .map(|char| text.chars().filter(|c| *c == char).count() as f32)
-                        .collect(),
-                ))
-            }
+            anyhow::ensure!(
+                !text.contains('g'),
+                "cannot embed text containing a 'g' character"
+            );
+            Ok(Embedding::new(
+                ('a'..='z')
+                    .map(|char| text.chars().filter(|c| *c == char).count() as f32)
+                    .collect(),
+            ))
         }));
 
         let (indexing_progress_tx, _) = channel::unbounded();

crates/semantic_index/src/summary_index.rs

@@ -543,7 +543,7 @@ impl SummaryIndex {
             .find(|model| &model.id() == &summary_model_id)
         else {
             return cx.background_spawn(async move {
-                Err(anyhow!("Couldn't find the preferred summarization model ({:?}) in the language registry's available models", summary_model_id))
+                anyhow::bail!("Couldn't find the preferred summarization model ({summary_model_id:?}) in the language registry's available models")
             });
         };
         let utf8_path = path.to_string_lossy();