Statically check that COMMON_STRINGS cannot cause overflows

boa-dev · Jun 30, 2022 · 0c2ef02 · 0c2ef02
1 parent b00bdf6
commit 0c2ef02
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Showing 4 changed files with 34 additions and 25 deletions.
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/boa_interner/Cargo.toml b/boa_interner/Cargo.toml
@@ -14,3 +14,4 @@ license = "Unlicense/MIT"
 serde = { version = "1.0.137", features = ["derive"], optional = true }
 phf = { version = "0.10.1", features = ["macros"] }
 rustc-hash = "1.1.0"
+static_assertions = "1.1.0"
diff --git a/boa_interner/src/lib.rs b/boa_interner/src/lib.rs
@@ -70,6 +70,8 @@
     rustdoc::missing_doc_code_examples
 )]
 
+extern crate static_assertions as sa;
+
 mod fixed_string;
 mod interned_str;
 mod sym;
@@ -263,8 +265,8 @@ impl Interner {
         COMMON_STRINGS.get_index(string).map(|idx|
             // SAFETY: `idx >= 0`, since it's an `usize`, and `idx + 1 > 0`.
             // In this case, we don't need to worry about overflows
-            // because `COMMON_STRINGS` would need to be of considerable
-            // size to cause an overflow, even on machines with `usize = u32`.
+            // because we have a static assertion in place checking that
+            // `COMMON_STRINGS.len() < usize::MAX`.
             unsafe {
                 Sym::new_unchecked(idx + 1)
             })

diff --git a/boa_interner/src/sym.rs b/boa_interner/src/sym.rs
@@ -117,27 +117,32 @@ impl Sym {
 ///
 /// `COMMON_STRINGS` and the constants defined in [`Sym`] must always
 /// be in sync.
-pub(super) static COMMON_STRINGS: phf::OrderedSet<&'static str> = phf::phf_ordered_set! {
-    "",
-    "arguments",
-    "await",
-    "yield",
-    "eval",
-    "default",
-    "null",
-    "RegExp",
-    "get",
-    "set",
-    "<main>",
-    "raw",
-    "static",
-    "prototype",
-    "constructor",
-    "implements",
-    "interface",
-    "let",
-    "package",
-    "private",
-    "protected",
-    "public",
+pub(super) static COMMON_STRINGS: phf::OrderedSet<&'static str> = {
+    const COMMON_STRINGS: phf::OrderedSet<&'static str> = phf::phf_ordered_set! {
+        "",
+        "arguments",
+        "await",
+        "yield",
+        "eval",
+        "default",
+        "null",
+        "RegExp",
+        "get",
+        "set",
+        "<main>",
+        "raw",
+        "static",
+        "prototype",
+        "constructor",
+        "implements",
+        "interface",
+        "let",
+        "package",
+        "private",
+        "protected",
+        "public",
+    };
+    // A `COMMON_STRINGS` of size `usize::MAX` would cause an overflow on our `Interner`
+    sa::const_assert!(COMMON_STRINGS.len() < usize::MAX);
+    COMMON_STRINGS
 };