primops: add builtins.rebaseHash

src/libexpr/primops.cc

@@ -3631,6 +3631,51 @@ static RegisterPrimOp primop_hashString({
     .fun = prim_hashString,
 });
 
+static void prim_rebaseHash(EvalState & state, const PosIdx pos, Value * * args, Value & v)
+{
+    auto type = state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.rebaseHash");
+    std::optional<HashType> ht = parseHashType(type);
+    if (!ht)
+        state.debugThrowLastTrace(Error({
+            .msg = hintfmt("unknown hash type '%1%'", type),
+            .errPos = state.positions[pos],
+        }));
+
+    auto base = state.forceStringNoCtx(*args[1], pos, "while evaluating the second argument passed to builtins.rebaseHash");
+    Base hb;
+    if (base == "sri") {
+        hb = SRI;
+    } else if (base == "base16") {
+        hb = Base16;
+    } else if (base == "base32") {
+        hb = Base32;
+    } else if (base == "base64") {
+        hb = Base64;
+    } else {
+        state.debugThrowLastTrace(Error({
+            .msg = hintfmt("unknown hash format '%1%'", base),
+            .errPos = state.positions[pos],
+        }));
+    }
+
+    PathSet context; // discarded
+    auto s = state.forceString(*args[2], context, pos, "while evaluating the third argument passed to builtins.rebaseHash");
+
+    v.mkString(Hash::parseAny(s, ht).to_string(hb, hb == SRI));
+}
+
+static RegisterPrimOp primop_rebaseHash({
+    .name = "__rebaseHash",
+    .args = {"type", "base", "s"},
+    .doc = R"(
+      Return a *base* representation of the hash *s*. The hash algorithm
+      specified by *type* must be one of `"md5"`, `"sha1"`, `"sha256"` or
+      `"sha512"`. The hash format specified by *base* must be one of
+      `"base16"`, `"base32"`, `"base64"` or `"sri"`.
+    )",
+    .fun = prim_rebaseHash,
+});
+
 struct RegexCache
 {
     // TODO use C++20 transparent comparison when available