From ca07652e7f168b7abdb6823ead83a2e93f4916b7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20F=C3=A4rber?= <01mf02@gmail.com>
Date: Thu, 18 Jan 2024 12:35:19 +0100
Subject: [PATCH] Turn a few `Vec<T>` into `Box<[T]>` to signal fixed length.

This was inspired by
<https://blog.polybdenum.com/2024/01/17/identifying-the-collect-vec-memory-leak-footgun.html>.
---
 jaq-interpret/src/filter.rs | 12 ++++++------
 jaq-interpret/src/lir.rs    |  6 +++---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/jaq-interpret/src/filter.rs b/jaq-interpret/src/filter.rs
index c1ac8f7ba..b05775999 100644
--- a/jaq-interpret/src/filter.rs
+++ b/jaq-interpret/src/filter.rs
@@ -9,11 +9,11 @@ use jaq_syn::{MathOp, OrdOp};
 
 /// Function from a value to a stream of value results.
 #[derive(Debug, Clone)]
-pub struct Owned(Id, Vec<Ast>);
+pub struct Owned(Id, Box<[Ast]>);
 
 impl Default for Owned {
     fn default() -> Self {
-        Self(Id(0), Vec::from([Ast::Id]))
+        Self(Id(0), Box::new([Ast::Id]))
     }
 }
 
@@ -41,12 +41,12 @@ pub(crate) struct Call {
     pub id: Id,
     pub typ: CallTyp,
     pub skip: usize,
-    pub args: Vec<Bind<Id, Id>>,
+    pub args: Box<[Bind<Id, Id>]>,
 }
 
 impl Owned {
     pub(crate) fn new(main: Id, recs: Vec<Ast>) -> Self {
-        Self(main, recs)
+        Self(main, recs.into())
     }
 }
 
@@ -61,7 +61,7 @@ pub(crate) enum Ast {
     Float(f64),
     Str(String),
     Array(Id),
-    Object(Vec<(Id, Id)>),
+    Object(Box<[(Id, Id)]>),
 
     Try(Id, Id),
     Neg(Id),
@@ -107,7 +107,7 @@ pub(crate) enum Ast {
     Var(usize),
     Call(Call),
 
-    Native(Native, Vec<Id>),
+    Native(Native, Box<[Id]>),
 }
 
 // we can unfortunately not make a `Box<dyn ... + Clone>`
diff --git a/jaq-interpret/src/lir.rs b/jaq-interpret/src/lir.rs
index 60ed9f312..d4ee88afd 100644
--- a/jaq-interpret/src/lir.rs
+++ b/jaq-interpret/src/lir.rs
@@ -59,7 +59,7 @@ fn recurse(typ: CallTyp) -> Filter {
         id: RECURSE,
         typ,
         skip: 0,
-        args: Vec::new(),
+        args: Default::default(),
     })
 }
 
@@ -67,7 +67,7 @@ impl Ctx {
     /// `{}[]` returns zero values.
     fn empty(&mut self) -> Filter {
         // `{}`
-        let obj = Filter::Object(Vec::new());
+        let obj = Filter::Object(Default::default());
         // `[]`
         let path = (path::Part::Range(None, None), path::Opt::Essential);
         Filter::Path(self.id_of_ast(obj), Path(Vec::from([path])))
@@ -156,7 +156,7 @@ impl Ctx {
                 match call {
                     mir::Call::Arg(a) if args.is_empty() => Filter::Var(a),
                     mir::Call::Arg(_) => panic!("higher-order argument encountered"),
-                    mir::Call::Native(n) => Filter::Native(n, args),
+                    mir::Call::Native(n) => Filter::Native(n, args.into()),
                     mir::Call::Def { id, skip, tail } => {
                         let callable = self.get_callable(id);
                         let args = callable.sig.args.iter().zip(args);