fix: a swap split across steps the user pays for shows every amount it spends (closes #625)

The swap's Amount line took only the first swap step's amount. It now
gives the total the steps take of Token In: the amount of the step that
sets the input side plus what each later step the user pays takes of it.
A take of another token, one after an amount that is not a quantity, or
one the decoder cannot tell, gets lines of its own; an unread take, a
V3_SWAP_EXACT_OUT's included, leaves no figure wherever it stands. A V4
step counts every SETTLE paid by the user and every SETTLE_ALL. A
PERMIT2_PERMIT names Token In, and its amount stands only in the plain
shape of Uniswap's own routes, with every later step read.

Model: opus-5-5

README.md

@@ -3180,15 +3180,16 @@ Currently supported:
   other than the one that sets the input side, whose input or one of whose
   `SETTLE`s or `SETTLE_ALL`s it cannot read, which the router still runs; a V2
   or V3 exact-in or V2 exact-out step or a `PERMIT2_TRANSFER_FROM` whose input
-  it cannot read; every `PERMIT2_TRANSFER_FROM_BATCH`; and, once the input side
-  is set, every `V3_SWAP_EXACT_OUT`, which the decoder does not read, and every
-  step it fails on. Each such step gives one `Moved from the sender` line among
-  those, reading `Unknown (could not be decoded)`. That line, or any line for a
-  token the decoder does not know, leaves no `Amount` line, whose figure might
-  be too low. Then each `PERMIT2_TRANSFER_FROM` but one into the router, in step
-  order, gives three lines: `Moved from the sender`, the amount it moves, for
-  example `1000000.0000 USDT`; `Token moved`, giving the token's address as the
-  `Token In` line does; and `Moved to`, which reads
+  it cannot read; every `PERMIT2_TRANSFER_FROM_BATCH`; every
+  `V3_SWAP_EXACT_OUT`, which the decoder does not read, wherever it stands; and
+  every step it fails on. Each such step gives one `Moved from the sender` line
+  among those, reading `Unknown (could not be decoded)`. That line, or any line
+  for a token the decoder does not know, leaves no `Amount` line, whose figure
+  might be too low, and such a step before a `PERMIT2_PERMIT` keeps the permit's
+  amount from standing. Then each `PERMIT2_TRANSFER_FROM` but one into the
+  router, in step order, gives three lines: `Moved from the sender`, the amount
+  it moves, for example `1000000.0000 USDT`; `Token moved`, giving the token's
+  address as the `Token In` line does; and `Moved to`, which reads
   `The V2 pair the next swap spends` for a hop and `The sender` for `address(1)`
   on every router but `UniversalRouterV1`, and otherwise gives the address. A
   move into the router needs none of them, because its `Paid to` line and

src/shared/uniswap.js

@@ -1234,10 +1234,11 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // V4 step, other than the one that sets the input side, whose input
         // or one of whose SETTLEs or SETTLE_ALLs it cannot read; a V2 or V3
         // exact-in or V2 exact-out step or PERMIT2_TRANSFER_FROM whose input
-        // it cannot read; a PERMIT2_TRANSFER_FROM_BATCH; and, once the input
-        // side is set, a V3_SWAP_EXACT_OUT or a step it fails on. It is
-        // recorded with a null token and amount: one line says so, and there
-        // is no Amount line, whose figure may then be too low.
+        // it cannot read; a PERMIT2_TRANSFER_FROM_BATCH; a V3_SWAP_EXACT_OUT;
+        // and a step it fails on. It is recorded with a null token and
+        // amount: one line says so, there is no Amount line, whose figure may
+        // then be too low, and the amount of a permit after it does not stand
+        // (see permitStands).
         const spentUnread = () => {
             userPaid.push({ token: null, amount: null });
         };
@@ -1489,11 +1490,11 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                 } else if (command === "V3_SWAP_EXACT_OUT") {
                     // This decoder does not read it
                     // (https://git.eeqj.de/sneak/AutistMask/issues/601). It
-                    // may pay any address and take from the sender, so once
-                    // the input side is set it leaves no Amount figure.
+                    // may pay any address and take from the sender, so
+                    // wherever it stands it leaves no Amount figure.
                     payeeUnread = true;
                     stepsUnread.push(i);
-                    if (inputEstablished) spentUnread();
+                    spentUnread();
                 } else if (command === "V2_SWAP_EXACT_IN") {
                     const s = decodeV2SwapExactIn(inputs[i]);
                     if (s) {
@@ -1749,7 +1750,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                 // take from the sender.
                 payeeUnread = true;
                 stepsUnread.push(i);
-                if (inputEstablished) spentUnread();
+                spentUnread();
             }
             if (allowedToFail) {
                 commandNames[i] += " (allowed to fail)";
@@ -1774,11 +1775,10 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // it in full (see stepsUnread). Permit2 then lets the router take no
         // more of the token than that amount, so the permit covers every take
         // of it. A later step this decoder did not read may raise what Permit2
-        // lets the router take, as a PERMIT2_PERMIT_BATCH can. A step this
-        // decoder does not read that may take from the sender leaves no
-        // figure, permit or not, when it comes after the step that sets the
-        // input side (see spentUnread()), and an EXECUTE_SUB_PLAN step leaves
-        // both sides unknown (below).
+        // lets the router take, as a PERMIT2_PERMIT_BATCH can. A step that
+        // may take from the sender what this decoder did not read leaves no
+        // figure, permit or not (see spentUnread()), and an EXECUTE_SUB_PLAN
+        // step leaves both sides unknown (below).
         const stepCommands = Array.from(
             commandsBytes,
             (b) => commands[b & commandTypeMask],

tests/uniswap.test.js

@@ -1876,23 +1876,69 @@ describe("uniswap decoder", () => {
             },
         );
 
-        // This decoder does not read a V3_SWAP_EXACT_OUT, so what one takes
-        // after the step that sets the input side leaves no Amount figure.
-        test("a V3 exact-in of 600 USDT, then a V3_SWAP_EXACT_OUT the user pays for, shows no Amount figure", () => {
-            // Its input is (recipient, amountOut, amountInMax, path,
-            // payerIsUser), laid out as encodeV3SwapExactIn() writes one; an
-            // exact-out path lists the token bought first.
-            const exactOut = encodeV3SwapExactIn(
-                USER_ADDR,
-                390000000n,
-                USDT_400,
-                [USDC_ADDR, USDT_ADDR],
-            );
-            const result = decodeSteps([0x00, 0x01], [V3_600, exactOut]);
-            expect(linesBetweenTokens(result)).toEqual([
-                ["Moved from the sender", UNDECODED],
+        // A V3_SWAP_EXACT_OUT the user pays for, of at most `amountInMax`
+        // USDT for USDC. Its input is (recipient, amountOut, amountInMax,
+        // path, payerIsUser), laid out as encodeV3SwapExactIn() writes one;
+        // an exact-out path lists the token bought first.
+        const v3ExactOut = (amountInMax) =>
+            encodeV3SwapExactIn(USER_ADDR, 390000000n, amountInMax, [
+                USDC_ADDR,
+                USDT_ADDR,
             ]);
-        });
+        // A split exact-out route: a V3_SWAP_EXACT_OUT of at most 6,000 USDT
+        // and a V2_SWAP_EXACT_OUT of at most 4,000 USDT, both paid by the
+        // user, then a SWEEP of USDC to the user.
+        const EXACT_OUT_SPLIT = [
+            v3ExactOut(6000000000n),
+            encodeV2SwapExactOut(USER_ADDR, 390000000n, 4000000000n, [
+                USDT_ADDR,
+                USDC_ADDR,
+            ]),
+            coder.encode(
+                ["address", "address", "uint256"],
+                [USDC_ADDR, USER_ADDR, 0n],
+            ),
+        ];
+        // This decoder does not read a V3_SWAP_EXACT_OUT, so what one takes
+        // leaves no Amount figure wherever it stands, and a permit's amount
+        // does not stand.
+        test.each([
+            {
+                kind: "a V3 exact-in of 600 USDT, then a V3_SWAP_EXACT_OUT",
+                commands: [0x00, 0x01],
+                inputs: [V3_600, v3ExactOut(USDT_400)],
+            },
+            {
+                kind: "a PERMIT2_PERMIT of 10,000 USDT, then a V3_SWAP_EXACT_OUT, a V2_SWAP_EXACT_OUT and a SWEEP",
+                commands: [0x0a, 0x01, 0x09, 0x04],
+                inputs: [
+                    encodePermit2(USDT_ADDR, 10000000000n, ROUTER_ADDR),
+                    ...EXACT_OUT_SPLIT,
+                ],
+            },
+            {
+                kind: "a V3_SWAP_EXACT_OUT, a V2_SWAP_EXACT_OUT and a SWEEP",
+                commands: [0x01, 0x09, 0x04],
+                inputs: EXACT_OUT_SPLIT,
+            },
+            {
+                kind: "a V3_SWAP_EXACT_OUT of at most 9,400 USDT, then a PERMIT2_PERMIT of 600 USDT and a V3 exact-in of 600 USDT",
+                commands: [0x01, 0x0a, 0x00],
+                inputs: [
+                    v3ExactOut(9400000000n),
+                    encodePermit2(USDT_ADDR, USDT_600, ROUTER_ADDR),
+                    V3_600,
+                ],
+            },
+        ])(
+            "$kind, all paid by the user, shows no Amount figure",
+            ({ commands, inputs }) => {
+                const result = decodeSteps(commands, inputs);
+                expect(linesBetweenTokens(result)).toEqual([
+                    ["Moved from the sender", UNDECODED],
+                ]);
+            },
+        );
 
         // A later step's amount that cannot be added to the Amount line,
         // because the amount of the step that set the input side is not a