fix: avoid to_candid on tuple expressions, unsupported in interpreter

Motoko's interpreter doesn't implement to_candid for tuple expression
types. Replace to_candid((k, v)) with separate to_candid(k) +
to_candid(v) calls throughout sampleMapBytes, sampleDownloadsMapBytes,
sampleSnapshotMapBytes, and the storage/users helpers. Also add explicit
: Nat return-type annotations to lambdas passed to sampleMapBytes so the
compiler can correctly type their block bodies.

Made-with: Cursor

Author: rvanasa

backend/main/DownloadLog.mo

@@ -442,7 +442,7 @@ module {
         var sampled = 0;
         for ((k, v) in map.entries()) {
           if (i % stride == 0) {
-            sum += (to_candid ((k, v)) : Blob).size();
+            sum += (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size();
             sampled += 1;
           };
           i += 1;
@@ -459,7 +459,7 @@ module {
         var sampled = 0;
         for ((k, buf) in map.entries()) {
           if (i % stride == 0) {
-            sum += (to_candid ((k, Buffer.toArray(buf))) : Blob).size();
+            sum += (to_candid (k) : Blob).size() + (to_candid (Buffer.toArray(buf)) : Blob).size();
             sampled += 1;
           };
           i += 1;

backend/main/Users.mo

@@ -34,7 +34,7 @@ module {
       var sampled = 0;
       for ((k, v) in _users.entries()) {
         if (i % stride == 0) {
-          sum += (to_candid ((k, v)) : Blob).size();
+          sum += (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size();
           sampled += 1;
         };
         i += 1;

backend/main/main-canister.mo

@@ -622,11 +622,11 @@ actor class Main() = this {
 
   let SAMPLE_SIZE : Nat = 10_000;
 
-  // Serializes a random sample of up to SAMPLE_SIZE entries and extrapolates
-  // the total byte count, keeping to_candid allocations bounded.
+  // Samples up to SAMPLE_SIZE entries and extrapolates the total byte count,
+  // keeping to_candid allocations bounded regardless of map size.
   func sampleMapBytes<K, V>(
     map : TrieMap.TrieMap<K, V>,
-    serialize : (K, V) -> Blob,
+    entryBytes : (K, V) -> Nat,
   ) : Nat {
     let total = map.size();
     if (total == 0) return 0;
@@ -636,7 +636,7 @@ actor class Main() = this {
     var sampled = 0;
     for ((k, v) in map.entries()) {
       if (i % stride == 0) {
-        sum += serialize(k, v).size();
+        sum += entryBytes(k, v);
         sampled += 1;
       };
       i += 1;
@@ -657,55 +657,55 @@ actor class Main() = this {
 
       packageVersions = {
         count = packageVersions.size();
-        bytes = sampleMapBytes(packageVersions, func(k : PackageName, v : [PackageVersion]) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageVersions, func(k : PackageName, v : [PackageVersion]) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packageConfigs = {
         count = packageConfigs.size();
-        bytes = sampleMapBytes(packageConfigs, func(k : PackageId, v : PackageConfigV3) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageConfigs, func(k : PackageId, v : PackageConfigV3) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       highestConfigs = {
         count = highestConfigs.size();
-        bytes = sampleMapBytes(highestConfigs, func(k : PackageName, v : PackageConfigV3) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(highestConfigs, func(k : PackageName, v : PackageConfigV3) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packagePublications = {
         count = packagePublications.size();
-        bytes = sampleMapBytes(packagePublications, func(k : PackageId, v : PackagePublication) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packagePublications, func(k : PackageId, v : PackagePublication) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       ownersByPackage = {
         count = ownersByPackage.size();
-        bytes = sampleMapBytes(ownersByPackage, func(k : PackageName, v : [Principal]) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(ownersByPackage, func(k : PackageName, v : [Principal]) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       maintainersByPackage = {
         count = maintainersByPackage.size();
-        bytes = sampleMapBytes(maintainersByPackage, func(k : PackageName, v : [Principal]) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(maintainersByPackage, func(k : PackageName, v : [Principal]) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       fileIdsByPackage = {
         count = fileIdsByPackage.size();
-        bytes = sampleMapBytes(fileIdsByPackage, func(k : PackageId, v : [FileId]) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(fileIdsByPackage, func(k : PackageId, v : [FileId]) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       hashByFileId = {
         count = hashByFileId.size();
-        bytes = sampleMapBytes(hashByFileId, func(k : FileId, v : Blob) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(hashByFileId, func(k : FileId, v : Blob) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packageFileStats = {
         count = packageFileStats.size();
-        bytes = sampleMapBytes(packageFileStats, func(k : PackageId, v : PackageFileStats) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageFileStats, func(k : PackageId, v : PackageFileStats) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packageTestStats = {
         count = packageTestStats.size();
-        bytes = sampleMapBytes(packageTestStats, func(k : PackageId, v : TestStats) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageTestStats, func(k : PackageId, v : TestStats) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packageBenchmarks = {
         count = packageBenchmarks.size();
-        bytes = sampleMapBytes(packageBenchmarks, func(k : PackageId, v : Benchmarks) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageBenchmarks, func(k : PackageId, v : Benchmarks) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packageNotes = {
         count = packageNotes.size();
-        bytes = sampleMapBytes(packageNotes, func(k : PackageId, v : Text) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageNotes, func(k : PackageId, v : Text) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
       packageDocsCoverage = {
         count = packageDocsCoverage.size();
-        bytes = sampleMapBytes(packageDocsCoverage, func(k : PackageId, v : Float) : Blob = to_candid ((k, v)));
+        bytes = sampleMapBytes(packageDocsCoverage, func(k : PackageId, v : Float) : Nat { (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size() });
       };
 
       downloadsByPackageName = dlStats.downloadsByPackageName;

backend/storage/storage-manager.mo

@@ -187,7 +187,7 @@ module {
         var sampled = 0;
         for ((k, v) in storages.entries()) {
           if (i % stride == 0) {
-            sum += (to_candid ((k, v)) : Blob).size();
+            sum += (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size();
             sampled += 1;
           };
           i += 1;
@@ -204,7 +204,7 @@ module {
         var sampled = 0;
         for ((k, v) in storageByFileId.entries()) {
           if (i % stride == 0) {
-            sum += (to_candid ((k, v)) : Blob).size();
+            sum += (to_candid (k) : Blob).size() + (to_candid (v) : Blob).size();
             sampled += 1;
           };
           i += 1;