Don't use separate temp dir for query jsons (2) (#2803)

* Don't use temp dir for query jsons

Fixes #2663

* Return early when exclusive create fails

* Use atomic-file-write for writing query data

FAQ.md

@@ -201,19 +201,6 @@ as an ergonomic choice it does _not_ block committing if `cargo sqlx prepare` fa
 We're working on a way for the macros to save their data to the filesystem automatically which should be part of SQLx 0.7,
 so your pre-commit hook would then just need to stage the changed files. This can be enabled by creating a directory 
 and setting the `SQLX_OFFLINE_DIR` environment variable to it before compiling. 
-Additionally, if you're not using Cargo or have a nonstandard setup, you may want to set the `SQLX_TMP`
-variable in order to store temporary query files somewhere that isn't picked up by git.
-These files should get cleaned up automatically, but they may not if there's a failure. For example:
-
-```shell
-$ mkdir .sqlx
-$ export SQLX_OFFLINE_DIR="./.sqlx"`
-$ # Optional and only useful if using a nonstandard setup, ensures temp files won't get picked up by git on failure
-$ mkdir ./my-custom-target/sqlx
-$ export SQLX_TMP="./my-custom-target/sqlx-tmp"
-$ cargo check
-```
-
 However, this behaviour is not considered stable and it is still recommended to use `cargo sqlx prepare`.
 
 ----

sqlx-cli/src/prepare.rs

@@ -171,7 +171,6 @@ fn run_prepare_step(ctx: &PrepareCtx, cache_dir: &Path) -> anyhow::Result<()> {
         check_command
             .arg("check")
             .args(&ctx.cargo_args)
-            .env("SQLX_TMP", tmp_dir)
             .env("DATABASE_URL", &ctx.connect_opts.database_url)
             .env("SQLX_OFFLINE", "false")
             .env("SQLX_OFFLINE_DIR", cache_dir);

sqlx-macros-core/Cargo.toml

@@ -48,6 +48,7 @@ tokio = { workspace = true, optional = true }
 
 dotenvy = { workspace = true }
 
+atomic-write-file = { version = "0.1" }
 hex = { version = "0.4.3" }
 heck = { version = "0.4", features = ["unicode"] }
 either = "1.6.1"

sqlx-macros-core/src/query/data.rs

@@ -150,31 +150,22 @@ where
         }
     }
 
-    pub(super) fn save_in(
-        &self,
-        dir: impl AsRef<Path>,
-        tmp_dir: impl AsRef<Path>,
-    ) -> crate::Result<()> {
-        // Output to a temporary file first, then move it atomically to avoid clobbering
-        // other invocations trying to write to the same path.
+    pub(super) fn save_in(&self, dir: impl AsRef<Path>) -> crate::Result<()> {
+        let path = dir.as_ref().join(format!("query-{}.json", self.hash));
+        let mut file = atomic_write_file::AtomicWriteFile::open(&path)
+            .map_err(|err| format!("failed to open the temporary file: {err:?}"))?;
 
-        // Use a temp directory inside the workspace to avoid potential issues
-        // with persisting the file across filesystems.
-        let mut tmp_file = tempfile::NamedTempFile::new_in(tmp_dir)
-            .map_err(|err| format!("failed to create query file: {err:?}"))?;
-
-        serde_json::to_writer_pretty(tmp_file.as_file_mut(), self)
+        serde_json::to_writer_pretty(file.as_file_mut(), self)
             .map_err(|err| format!("failed to serialize query data to file: {err:?}"))?;
-        // Ensure there is a newline at the end of the JSON file to avoid accidental modification by IDE
-        // and make github diff tool happier
-        tmp_file
-            .as_file_mut()
+
+        // Ensure there is a newline at the end of the JSON file to avoid
+        // accidental modification by IDE and make github diff tool happier.
+        file.as_file_mut()
             .write_all(b"\n")
             .map_err(|err| format!("failed to append a newline to file: {err:?}"))?;
 
-        tmp_file
-            .persist(dir.as_ref().join(format!("query-{}.json", self.hash)))
-            .map_err(|err| format!("failed to move query file: {err:?}"))?;
+        file.commit()
+            .map_err(|err| format!("failed to commit the query data to {path:?}: {err:?}"))?;
 
         Ok(())
     }

sqlx-macros-core/src/query/mod.rs

@@ -356,19 +356,6 @@ where
         if let Ok(dir) = env("SQLX_OFFLINE_DIR") {
             let path = PathBuf::from(&dir);
 
-            // Prefer SQLX_TMP if set explicitly.
-            // Otherwise fallback to CARGO_TARGET_DIR and then the standard target directory.
-            let tmp_dir = if let Ok(tmp_dir) = env("SQLX_TMP") {
-                PathBuf::from(tmp_dir)
-            } else if let Ok(target_dir) = env("CARGO_TARGET_DIR") {
-                PathBuf::from(target_dir)
-            } else {
-                let tmp_target = PathBuf::from("./target/sqlx");
-                fs::create_dir_all(&tmp_target)
-                    .map_err(|e| format!("Error creating cache directory: {e:?}"))?;
-                tmp_target
-            };
-
             match fs::metadata(&path) {
                 Err(e) => {
                     if e.kind() != io::ErrorKind::NotFound {
@@ -387,7 +374,7 @@ where
                     }
 
                     // .sqlx exists and is a directory, store data.
-                    data.save_in(path, tmp_dir)?;
+                    data.save_in(path)?;
                 }
             }
         }