update command should not override the config file in some cases

crates/cli/src/lib.rs

@@ -13,6 +13,8 @@ use tokio::fs;
 use ndc_postgres_configuration as configuration;
 use ndc_postgres_configuration::environment::Environment;
 
+const UPDATE_ATTEMPTS: u8 = 3;
+
 /// The various contextual bits and bobs we need to run.
 pub struct Context<Env: Environment> {
     pub context_path: PathBuf,
@@ -128,30 +130,65 @@ async fn initialize(with_metadata: bool, context: Context<impl Environment>) ->
 ///
 /// This expects a configuration with a valid connection URI.
 async fn update(context: Context<impl Environment>) -> anyhow::Result<()> {
-    let configuration_file_path = context
-        .context_path
-        .join(configuration::CONFIGURATION_FILENAME);
-    let input: configuration::RawConfiguration = {
-        let configuration_file_contents = fs::read_to_string(&configuration_file_path)
-            .await
-            .map_err(|err| {
-                if err.kind() == std::io::ErrorKind::NotFound {
-                    anyhow::anyhow!(
-                        "{}: No such file or directory. Perhaps you meant to 'initialize' first?",
-                        configuration_file_path.display()
-                    )
-                } else {
-                    anyhow::anyhow!(err)
-                }
-            })?;
-        serde_json::from_str(&configuration_file_contents)?
-    };
-    let output = configuration::introspect(input, &context.environment).await?;
+    // It is possible to change the file in the middle of introspection.
+    // We want to detect these scenario and try again, or fail if we are unable to.
+    // We do that with a few attempts.
+    for _attempt in 1..UPDATE_ATTEMPTS {
+        let configuration_file_path = context
+            .context_path
+            .join(configuration::CONFIGURATION_FILENAME);
+        let input: configuration::RawConfiguration = {
+            let configuration_file_contents =
+                read_config_file_contents(&configuration_file_path).await?;
+            serde_json::from_str(&configuration_file_contents)?
+        };
+        let output = configuration::introspect(input.clone(), &context.environment).await?;
 
-    fs::write(
-        &configuration_file_path,
-        serde_json::to_string_pretty(&output)?,
-    )
-    .await?;
-    Ok(())
+        // Check that the input file did not change since we started introspecting.
+        let input_again_before_write: configuration::RawConfiguration = {
+            let configuration_file_contents =
+                read_config_file_contents(&configuration_file_path).await?;
+            serde_json::from_str(&configuration_file_contents)?
+        };
+
+        if input_again_before_write != input {
+            println!("Input file changed before write, trying again.");
+            // next attempt
+            continue;
+        }
+
+        // If the introspection result is different than the current config,
+        // change it. Otherwise, continue.
+        if input != output {
+            fs::write(
+                &configuration_file_path,
+                serde_json::to_string_pretty(&output)?,
+            )
+            .await?;
+        } else {
+            println!("The configuration is up-to-date. Nothing to do.");
+        }
+
+        return Ok(());
+    }
+
+    // We ran out of attempts.
+    Err(anyhow::anyhow!(
+        "Cannot override configuration: input changed before write."
+    ))
+}
+
+async fn read_config_file_contents(configuration_file_path: &PathBuf) -> anyhow::Result<String> {
+    fs::read_to_string(configuration_file_path)
+        .await
+        .map_err(|err| {
+            if err.kind() == std::io::ErrorKind::NotFound {
+                anyhow::anyhow!(
+                    "{}: No such file or directory. Perhaps you meant to 'initialize' first?",
+                    configuration_file_path.display()
+                )
+            } else {
+                anyhow::anyhow!(err)
+            }
+        })
 }

crates/configuration/src/configuration.rs

@@ -17,7 +17,7 @@ pub const CONFIGURATION_FILENAME: &str = "configuration.json";
 pub const CONFIGURATION_JSONSCHEMA_FILENAME: &str = "schema.json";
 
 /// The parsed connector configuration.
-#[derive(Clone, Debug, Deserialize, Serialize, JsonSchema)]
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize, JsonSchema)]
 #[serde(tag = "version")]
 pub enum RawConfiguration {
     #[serde(rename = "3")]

crates/configuration/src/values/isolation_level.rs

@@ -2,7 +2,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 /// The isolation level of the transaction in which a query is executed.
-#[derive(Debug, Clone, Copy, Default, Deserialize, Serialize, JsonSchema)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Default, Deserialize, Serialize, JsonSchema)]
 pub enum IsolationLevel {
     /// Prevents reading data from another uncommitted transaction.
     #[default]

crates/configuration/src/values/pool_settings.rs

@@ -2,7 +2,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 /// Settings for the PostgreSQL connection pool
-#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct PoolSettings {
     /// maximum number of pool connections

crates/configuration/src/version3/comparison.rs

@@ -5,7 +5,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 /// Define the names that comparison operators will be exposed as by the automatic introspection.
-#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema)]
+#[derive(Debug, PartialEq, Eq, Clone, Deserialize, Serialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct ComparisonOperatorMapping {
     /// The name of the operator as defined by the database

crates/configuration/src/version3/connection_settings.rs

@@ -7,7 +7,7 @@ use serde::{Deserialize, Serialize};
 pub const DEFAULT_CONNECTION_URI_VARIABLE: &str = "CONNECTION_URI";
 
 /// Database connection settings.
-#[derive(Clone, Debug, Deserialize, Serialize, JsonSchema)]
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct DatabaseConnectionSettings {
     /// Connection string for a Postgres-compatible database.

crates/configuration/src/version3/mod.rs

@@ -24,7 +24,7 @@ const CONFIGURATION_QUERY: &str = include_str!("version3.sql");
 
 /// Initial configuration, just enough to connect to a database and elaborate a full
 /// 'Configuration'.
-#[derive(Clone, Debug, Deserialize, Serialize, JsonSchema)]
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct RawConfiguration {
     /// Jsonschema of the configuration format.

crates/configuration/src/version3/options.rs

@@ -6,7 +6,7 @@ use serde::{Deserialize, Serialize};
 use super::comparison::ComparisonOperatorMapping;
 
 /// Options which only influence how the configuration is updated.
-#[derive(Clone, Debug, Deserialize, Serialize, JsonSchema)]
+#[derive(Clone, PartialEq, Eq, Debug, Deserialize, Serialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct IntrospectionOptions {
     /// Schemas which are excluded from introspection. The default setting will exclude the

crates/query-engine/metadata/src/metadata/database.rs

@@ -5,7 +5,7 @@ use serde::{Deserialize, Serialize};
 use std::collections::{BTreeMap, BTreeSet};
 
 /// Map of all known composite types.
-#[derive(Debug, Clone, PartialEq, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Debug, Clone, PartialEq, Eq, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct CompositeTypes(pub BTreeMap<String, CompositeType>);
 
@@ -79,7 +79,7 @@ fn default_true() -> bool {
 }
 
 /// Mapping from a "table" name to its information.
-#[derive(Debug, Clone, PartialEq, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Debug, Clone, PartialEq, Eq, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct TablesInfo(pub BTreeMap<String, TableInfo>);
 

crates/query-engine/metadata/src/metadata/mod.rs

@@ -12,7 +12,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 /// Metadata information.
-#[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, PartialEq, Eq, Debug, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct Metadata {
     #[serde(default)]

crates/query-engine/metadata/src/metadata/mutations.rs

@@ -4,7 +4,7 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 /// Which version of the generated mutations will be included in the schema
-#[derive(Debug, Clone, Copy, Deserialize, Serialize, JsonSchema)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Deserialize, Serialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub enum MutationsVersion {
     V1,

crates/query-engine/metadata/src/metadata/native_queries.rs

@@ -9,7 +9,7 @@ use std::collections::BTreeMap;
 // Types
 
 /// Metadata information of native queries.
-#[derive(Debug, Clone, PartialEq, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Debug, Clone, PartialEq, Eq, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "camelCase")]
 pub struct NativeQueries(pub BTreeMap<String, NativeQueryInfo>);