libexpr: fix elided value counting in printer

using the total-attrs-printed and total-list-items-printed counters to
calculate how many attrs were elided only works properly if no nesting
is involved. once things do nest the global counter can exceed the size
of the currently printed object, leading to unsigned wrapping and great
overestimation of elided counts. counting locally in addition to global
counts fixes this.

these are functional tests because creating these objects requires the
evaluator to not be a huge amount of code, and we also want defaults to
be tested for cli usage.

fixes #14

Change-Id: Icb9a0cb21b2f4bacbc5e9dcdd8c0b9055b4088a7

6 files changed, 39 insertions, 3 deletions

diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index 7ef21dfa9..71ab1edbf 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -337,11 +337,12 @@ private:
 
             auto prettyPrint = shouldPrettyPrintAttrs(sorted);
 
+            size_t printedHere = 0;
             for (auto & i : sorted) {
                 printSpace(prettyPrint);
 
                 if (attrsPrinted >= options.maxAttrs) {
-                    printElided(sorted.size() - attrsPrinted, "attribute", "attributes");
+                    printElided(sorted.size() - printedHere, "attribute", "attributes");
                     break;
                 }
 
@@ -350,6 +351,7 @@ private:
                 print(*i.second, depth + 1);
                 output << ";";
                 attrsPrinted++;
+                printedHere++;
             }
 
             decreaseIndent();
@@ -394,11 +396,12 @@ private:
             output << "[";
             auto listItems = v.listItems();
             auto prettyPrint = shouldPrettyPrintList(listItems);
+            size_t printedHere = 0;
             for (auto elem : listItems) {
                 printSpace(prettyPrint);
 
                 if (listItemsPrinted >= options.maxListItems) {
-                    printElided(v.listSize() - listItemsPrinted, "item", "items");
+                    printElided(v.listSize() - printedHere, "item", "items");
                     break;
                 }
 
@@ -408,6 +411,7 @@ private:
                     printNullptr();
                 }
                 listItemsPrinted++;
+                printedHere++;
             }
 
             decreaseIndent();
diff --git a/tests/functional/lang/eval-fail-bad-string-interpolation-4.err.exp b/tests/functional/lang/eval-fail-bad-string-interpolation-4.err.exp
index 6f907106b..b262e814d 100644
--- a/tests/functional/lang/eval-fail-bad-string-interpolation-4.err.exp
+++ b/tests/functional/lang/eval-fail-bad-string-interpolation-4.err.exp
@@ -6,4 +6,4 @@ error:
              |   ^
            10|
 
-       error: cannot coerce a set to a string: { a = { a = { a = { a = "ha"; b = "ha"; c = "ha"; d = "ha"; e = "ha"; f = "ha"; g = "ha"; h = "ha"; j = "ha"; }; «4294967295 attributes elided» }; «4294967294 attributes elided» }; «4294967293 attributes elided» }
+       error: cannot coerce a set to a string: { a = { a = { a = { a = "ha"; b = "ha"; c = "ha"; d = "ha"; e = "ha"; f = "ha"; g = "ha"; h = "ha"; j = "ha"; }; «8 attributes elided» }; «8 attributes elided» }; «8 attributes elided» }
diff --git a/tests/functional/lang/eval-fail-print-limit-list.err.exp b/tests/functional/lang/eval-fail-print-limit-list.err.exp
new file mode 100644
index 000000000..2f347d15a
--- /dev/null
+++ b/tests/functional/lang/eval-fail-print-limit-list.err.exp
@@ -0,0 +1,12 @@
+error:
+       … in the condition of the assert statement
+         at /pwd/lang/eval-fail-print-limit-list.nix:1:1:
+            1| assert (
+             | ^
+            2|   let x = [ 1 [ 2 3 4 5 6 7 8 9 x 10 11 ] 12 ];
+
+       error: expected a Boolean but found a list: [ 1 [ 2 3 4 5 6 7 8 9 [ 1 «2 items elided» ] «2 items elided» ] «1 item elided» ]
+       at /pwd/lang/eval-fail-print-limit-list.nix:1:1:
+            1| assert (
+             | ^
+            2|   let x = [ 1 [ 2 3 4 5 6 7 8 9 x 10 11 ] 12 ];
diff --git a/tests/functional/lang/eval-fail-print-limit-list.nix b/tests/functional/lang/eval-fail-print-limit-list.nix
new file mode 100644
index 000000000..14715f04d
--- /dev/null
+++ b/tests/functional/lang/eval-fail-print-limit-list.nix
@@ -0,0 +1,4 @@
+assert (
+  let x = [ 1 [ 2 3 4 5 6 7 8 9 x 10 11 ] 12 ];
+  in builtins.deepSeq x x
+); 1
diff --git a/tests/functional/lang/eval-fail-print-limit-set.err.exp b/tests/functional/lang/eval-fail-print-limit-set.err.exp
new file mode 100644
index 000000000..c5086fb76
--- /dev/null
+++ b/tests/functional/lang/eval-fail-print-limit-set.err.exp
@@ -0,0 +1,12 @@
+error:
+       … in the condition of the assert statement
+         at /pwd/lang/eval-fail-print-limit-set.nix:1:1:
+            1| assert (
+             | ^
+            2|   let x = { a.a.a.a.a.a.a.a.a = { a.a = 1; b = 2; }; a.b.c.x = 3; c = 4; };
+
+       error: expected a Boolean but found a set: { a = { a = { a = { a = { a = { a = { a = { a = { a = { a = { ... }; b = 2; }; }; }; }; }; }; }; }; «1 attribute elided» }; «1 attribute elided» }
+       at /pwd/lang/eval-fail-print-limit-set.nix:1:1:
+            1| assert (
+             | ^
+            2|   let x = { a.a.a.a.a.a.a.a.a = { a.a = 1; b = 2; }; a.b.c.x = 3; c = 4; };
diff --git a/tests/functional/lang/eval-fail-print-limit-set.nix b/tests/functional/lang/eval-fail-print-limit-set.nix
new file mode 100644
index 000000000..b268cb7f7
--- /dev/null
+++ b/tests/functional/lang/eval-fail-print-limit-set.nix
@@ -0,0 +1,4 @@
+assert (
+  let x = { a.a.a.a.a.a.a.a.a = { a.a = 1; b = 2; }; a.b.c.x = 3; c = 4; };
+  in builtins.deepSeq x x
+); 1