3 files changed, 36 insertions, 16 deletions
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.exp
index a148ebc3b53f..cd5a6c0d5490 100644
--- a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.exp
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.exp
@@ -1 +1 @@
-[ "1" "4.200000" "" "" "1" "foo" "/etc" "Hello World" "Hello World" "1" "out" "2" "1 4.200000   1 foo /etc Hello World Hello World 1 out 2" ]
+[ "" " " " /deep/thought" " 2  3" " flat" "1" "4.200000" "" "" "1" "foo" "/etc" "Hello World" "Hello World" "1" "out" "2" "    /deep/thought  2  3  flat 1 4.200000   1 foo /etc Hello World Hello World 1 out 2" ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.nix
index e4dc18ac96a7..eb8011158fd0 100644
--- a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.nix
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-toString.nix
@@ -5,19 +5,24 @@ let
   };
 
   toStringExamples = [
-    (toString 1)
-    (toString 4.2)
-    (toString null)
-    (toString false)
-    (toString true)
-    (toString "foo")
-    (toString /etc)
-    (toString toStringableSet)
-    (toString { __toString = _: toStringableSet; })
-    (toString { __toString = _: true; })
-    (toString { outPath = "out"; })
-    (toString { outPath = { outPath = { __toString = _: 2; }; }; })
+    null
+    [ null false ]
+    [ null /deep/thought ]
+    [ [ null 2 ] null 3 ]
+    [ false "flat" ]
+    1
+    4.2
+    null
+    false
+    true
+    "foo"
+    /etc
+    toStringableSet
+    { __toString = _: toStringableSet; }
+    { __toString = _: true; }
+    { outPath = "out"; }
+    { outPath = { outPath = { __toString = _: 2; }; }; }
   ];
 in
 
-toStringExamples ++ [ (toString toStringExamples) ]
+(builtins.map toString toStringExamples) ++ [ (toString toStringExamples) ]
diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs
index 0007735cc096..567a2f3df21b 100644
--- a/tvix/eval/src/value/mod.rs
+++ b/tvix/eval/src/value/mod.rs
@@ -315,6 +315,9 @@ impl Value {
     ) -> Result<Value, ErrorKind> {
         let mut result = String::new();
         let mut vals = vec![self];
+        // Track if we are coercing the first value of a list to correctly emit
+        // separating white spaces.
+        let mut is_list_head = None;
         loop {
             let value = if let Some(v) = vals.pop() {
                 v.force(co, span.clone()).await?
@@ -392,6 +395,12 @@ impl Value {
                     for elem in list.into_iter().rev() {
                         vals.push(elem);
                     }
+                    // In case we are coercing a list within a list we don't want
+                    // to touch this. Since the algorithm is nonrecursive, the
+                    // space would not have been created yet (due to continue).
+                    if is_list_head.is_none() {
+                        is_list_head = Some(true);
+                    }
                     continue;
                 }
 
@@ -419,9 +428,15 @@ impl Value {
                     panic!("tvix bug: .coerce_to_string() called on internal value")
                 }
             };
-            if !result.is_empty() {
-                result.push(' ');
+
+            if let Some(head) = is_list_head {
+                if !head {
+                    result.push(' ');
+                } else {
+                    is_list_head = Some(false);
+                }
             }
+
             result.push_str(&coerced?);
         }
     }