fix: build generates different IDs every time

e2e/bats/build.bash

@@ -58,3 +58,10 @@ teardown() {
     assert_command_fail dfx build
     assert_match 'import error, canister alias "random" not defined'
 }
+
+@test "build generates IDs every rebuild" {
+  assert_command dfx build
+  cp canisters/e2e_project/_canister.id previous_cid
+  assert_command dfx build
+  assert_command_fail diff canisters/e2e_project/_canister.id previous_cid
+}

src/dfx/src/commands/build.rs

@@ -32,7 +32,10 @@ pub fn exec(env: &dyn Environment, args: &ArgMatches<'_>) -> DfxResult {
     let canister_pool = CanisterPool::load(env)?;
     // First build.
     slog::info!(logger, "Building canisters...");
-    canister_pool.build_or_fail(BuildConfig::from_config(config.get_config()))?;
+
+    // TODO: remove the forcing of generating canister id once we have an update flow.
+    canister_pool
+        .build_or_fail(BuildConfig::from_config(config.get_config()).with_generate_id(true))?;
 
     // If there is not a package.json, we don't have a frontend and can quit early.
     if !config.get_project_root().join("package.json").exists() || args.is_present("skip-frontend")

src/dfx/src/lib/builders/mod.rs

@@ -58,6 +58,7 @@ pub trait CanisterBuilder {
 pub struct BuildConfig {
     profile: Profile,
     assets: bool,
+    pub generate_id: bool,
     metadata: BTreeMap<String, serde_json::Value>,
 }
 
@@ -66,13 +67,21 @@ impl BuildConfig {
         BuildConfig {
             profile: config.profile.unwrap_or(Profile::Debug),
             assets: false,
+            generate_id: false,
             metadata: BTreeMap::new(),
         }
     }
 
     pub fn with_assets(self, assets: bool) -> Self {
         Self { assets, ..self }
     }
+
+    pub fn with_generate_id(self, generate_id: bool) -> Self {
+        Self {
+            generate_id,
+            ..self
+        }
+    }
 }
 
 pub struct BuilderPool {

src/dfx/src/lib/models/canister.rs

@@ -102,6 +102,42 @@ impl CanisterPool {
         None
     }
 
+    pub fn generate_canister_id(&self, force: bool) -> DfxResult {
+        // Write all canister IDs if needed.
+        for canister in &self.canisters {
+            let canister_info = &canister.info;
+
+            let canister_id = if force {
+                None
+            } else {
+                canister_info.get_canister_id()
+            };
+            let canister_id = match canister_id {
+                Some(cid) => cid,
+                None => {
+                    std::fs::create_dir_all(
+                        canister_info
+                            .get_canister_id_path()
+                            .parent()
+                            .expect("Cannot use root."),
+                    )?;
+                    let cid = canister_info.generate_canister_id()?;
+                    std::fs::write(
+                        canister_info.get_canister_id_path(),
+                        cid.clone().into_blob().0,
+                    )
+                    .map_err(DfxError::from)?;
+
+                    cid
+                }
+            };
+
+            slog::debug!(self.logger, "  {} => {}", canister.get_name(), canister_id);
+        }
+
+        Ok(())
+    }
+
     fn build_dependencies_graph(&self) -> DfxResult<DiGraph<CanisterId, ()>> {
         let mut graph: DiGraph<CanisterId, ()> = DiGraph::new();
         let mut id_set: BTreeMap<CanisterId, NodeIndex<u32>> = BTreeMap::new();
@@ -146,24 +182,8 @@ impl CanisterPool {
 
     /// Build all canisters, returning a vector of results of each builds.
     pub fn build(&self, build_config: BuildConfig) -> DfxResult<Vec<DfxResult<BuildOutput>>> {
-        // Write all canister IDs if needed.
-        for canister in &self.canisters {
-            slog::debug!(self.logger, "  '{}'", canister.get_name());
-            let canister_info = &canister.info;
-
-            if canister_info.get_canister_id().is_none() {
-                std::fs::create_dir_all(
-                    canister_info
-                        .get_canister_id_path()
-                        .parent()
-                        .expect("Cannot use root."),
-                )?;
-                std::fs::write(
-                    canister_info.get_canister_id_path(),
-                    canister_info.generate_canister_id()?.into_blob().0,
-                )
-                .map_err(DfxError::from)?;
-            }
+        if build_config.generate_id {
+            self.generate_canister_id(true)?;
         }
 
         let graph = self.build_dependencies_graph()?;