[test] Repro for GC thrashing

This is bug #2123.

Unrelated:

[spec/ysh-builtin-eval] Nicer example

spec/ysh-builtin-eval.test.sh

@@ -669,7 +669,7 @@ var s = io->evalExpr(ex, dollar0='z', pos_args=:|a b c|, vars=vars)
 
 echo $s
 
-proc where(; pred) {
+proc my-where (; pred) {
   # note: for line in (io.stdin) is messed up by spec test framework
 
   while read --raw-line (&line) {
@@ -682,10 +682,18 @@ proc where(; pred) {
   }
 }
 
-seq 5 | where [_line ~== 2 or _line ~== 4]
+
+seq 5 | my-where [_line ~== 2 or _line ~== 4]
+echo ---
+
+seq 5 10 | my-where [_line % 2 === 1]
 
 ## STDOUT:
 z a b hello
 2
 4
+---
+5
+7
+9
 ## END

test/bug-2123.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+demo() {
+  local ysh=_bin/cxx-opt/ysh
+  ninja $ysh
+
+  #OILS_GC_STATS=1 $ysh test/bug-2123.ysh
+
+  # max RSS
+  # 246
+  /usr/bin/time --format '%e %M' $ysh test/bug-2123.ysh
+}
+
+"$@"

test/bug-2123.ysh

@@ -0,0 +1,78 @@
+# Run with _bin/cxx-opt/ysh
+
+proc filter (; predicate) {
+	for line in (io.stdin) {
+		if (io->evalExpr(predicate, vars={_val: fromJson8(line)})) {
+			write -- $line
+		}
+	}
+}
+
+#
+# Setup
+#
+
+var f = '_tmp/b1'
+
+for i in (0 ..= 100_000) {
+	json write ({}, space=0)
+} > $f
+
+#
+# Benchmarks
+#
+
+var N = 2
+
+proc with-default {
+  write -- u'get() with default\n'
+  write -- 'BEFORE ------------------------------------------------------'
+
+  for _ in (0 ..< N) {
+    time for line in (io.stdin) {
+      call fromJson8(line)
+    } < $f
+    write
+  }
+
+  echo 'FILTER with default'
+  time filter [get(_val, 'missing-key', 0) === 0] < $f >/dev/null
+
+  write -- 'AFTER -------------------------------------------------------'
+
+  for _ in (0 ..< N) {
+    time for line in (io.stdin) {
+      call fromJson8(line)
+    } < $f
+    write
+  }
+}
+
+proc without-default {
+  write -- u'get() without default\n'
+  write -- 'BEFORE ------------------------------------------------------'
+
+  for _ in (0 ..< N) {
+    time for line in (io.stdin) {
+      call fromJson8(line)
+    } < $f
+    write
+  }
+
+  echo 'FILTER without default'
+  time filter [get(_val, 'missing-key')] < $f #>/dev/null
+
+  write -- 'AFTER -------------------------------------------------------'
+
+  for _ in (0 ..< N) {
+    time for line in (io.stdin) {
+      call fromJson8(line)
+    } < $f
+    write
+  }
+}
+
+
+with-default
+without-default
+

test/ysh-runtime-errors.sh

@@ -406,6 +406,10 @@ test-eggex-convert-func() {
   _ysh-expr-error 'var pat = / <capture d+: evalExpr> /; var m = "10" => search(pat) => group(1)'
 }
 
+test-eval-expr() {
+  _ysh-expr-error 'var expr = ^[x + 1]; = io->evalExpr(expr, pos_args=[42])'
+}
+
 test-int-convert() {
   _ysh-expr-error '= int({})'
   _ysh-expr-error '= int([])'