Allow renaming URL path parameters from the Params tab (#528)

apps/yaak-client/components/HttpRequestPane.tsx

@@ -1,5 +1,5 @@
 import type { HttpRequest } from "@yaakapp-internal/models";
-import { patchModel } from "@yaakapp-internal/models";
+import { getModel, patchModel } from "@yaakapp-internal/models";
 import type { GenericCompletionOption } from "@yaakapp-internal/plugins";
 import classNames from "classnames";
 import { atom, useAtomValue } from "jotai";
@@ -19,7 +19,7 @@ import { useSendAnyHttpRequest } from "../hooks/useSendAnyHttpRequest";
 import { deepEqualAtom } from "../lib/atoms";
 import { languageFromContentType } from "../lib/contentType";
 import { generateId } from "../lib/generateId";
-import { extractPathPlaceholders } from "../lib/pathPlaceholders";
+import { derivePathPlaceholderPairs, renamePathPlaceholder } from "../lib/pathPlaceholders";
 import { convertRequestBody } from "../lib/requestBodyConversion";
 import {
   BODY_TYPE_BINARY,
@@ -42,7 +42,6 @@ import type { GenericCompletionConfig } from "./core/Editor/genericCompletion";
 import { getUrlCompletionConfig } from "./core/Editor/url/completion";
 import { Editor } from "./core/Editor/LazyEditor";
 import { InlineCode } from "@yaakapp-internal/ui";
-import type { Pair } from "./core/PairEditor";
 import { PlainInput } from "./core/PlainInput";
 import type { TabItem, TabsRef } from "./core/Tabs/Tabs";
 import { setActiveTab, TabContent, Tabs } from "./core/Tabs/Tabs";
@@ -133,20 +132,33 @@ export function HttpRequestPane({ style, fullHeight, className, activeRequest }:
     [activeRequest],
   );
 
-  const { urlParameterPairs, urlParametersKey } = useMemo(() => {
-    const placeholderNames = extractPathPlaceholders(activeRequest.url);
-    const nonEmptyParameters = activeRequest.urlParameters.filter((p) => p.name || p.value);
-    const items: Pair[] = [...nonEmptyParameters];
-    for (const name of placeholderNames) {
-      const item = items.find((p) => p.name === name);
-      if (item) {
-        item.readOnlyName = true;
-      } else {
-        items.push({ name, value: "", enabled: true, readOnlyName: true, id: generateId() });
-      }
-    }
-    return { urlParameterPairs: items, urlParametersKey: placeholderNames.join(",") };
-  }, [activeRequest.url, activeRequest.urlParameters]);
+  // Renaming a path placeholder has to rewrite the URL and rename the parameter together, or the
+  // value detaches from the placeholder.
+  // NOTE: Reads the request fresh rather than closing over `activeRequest`. The row that calls this
+  //  holds onto it until the URL's placeholders change, so a captured request would go stale and
+  //  patch its parameter list back over newer edits.
+  const handleRenamePathPlaceholder = useCallback(
+    (oldName: string, newName: string) => {
+      const request = getModel("http_request", activeRequestId);
+      if (request == null) return false;
+
+      const patch = renamePathPlaceholder(request, oldName, newName);
+      if (patch == null) return false; // Unusable name, so the editor reverts the field
+      void patchModel(request, patch);
+      return true;
+    },
+    [activeRequestId],
+  );
+
+  const { urlParameterPairs, urlParametersKey } = useMemo(
+    () =>
+      derivePathPlaceholderPairs(
+        activeRequest.url,
+        activeRequest.urlParameters,
+        handleRenamePathPlaceholder,
+      ),
+    [activeRequest.url, activeRequest.urlParameters, handleRenamePathPlaceholder],
+  );
 
   let numParams = 0;
   if (

apps/yaak-client/components/UrlParameterEditor.tsx

@@ -1,15 +1,14 @@
-import type { HttpRequest } from "@yaakapp-internal/models";
 import { VStack } from "@yaakapp-internal/ui";
 import { useCallback, useRef } from "react";
 import { useRequestEditor, useRequestEditorEvent } from "../hooks/useRequestEditor";
-import type { PairEditorHandle, PairEditorProps } from "./core/PairEditor";
+import type { EditablePair, PairEditorHandle, PairEditorProps } from "./core/PairEditor";
 import { PairOrBulkEditor } from "./core/PairOrBulkEditor";
 
 type Props = {
   forceUpdateKey: string;
-  pairs: HttpRequest["headers"];
+  pairs: EditablePair[];
   stateKey: PairEditorProps["stateKey"];
-  onChange: (headers: HttpRequest["urlParameters"]) => void;
+  onChange: PairEditorProps["onChange"];
 };
 
 export function UrlParametersEditor({ pairs, forceUpdateKey, onChange, stateKey }: Props) {

apps/yaak-client/components/WebsocketRequestPane.tsx

@@ -1,5 +1,5 @@
 import type { WebsocketRequest } from "@yaakapp-internal/models";
-import { patchModel } from "@yaakapp-internal/models";
+import { getModel, patchModel } from "@yaakapp-internal/models";
 import type { GenericCompletionOption } from "@yaakapp-internal/plugins";
 import { closeWebsocket, connectWebsocket, sendWebsocket } from "@yaakapp-internal/ws";
 import classNames from "classnames";
@@ -20,8 +20,7 @@ import { useRequestEditor, useRequestEditorEvent } from "../hooks/useRequestEdit
 import { useRequestUpdateKey } from "../hooks/useRequestUpdateKey";
 import { deepEqualAtom } from "../lib/atoms";
 import { languageFromContentType } from "../lib/contentType";
-import { generateId } from "../lib/generateId";
-import { extractPathPlaceholders } from "../lib/pathPlaceholders";
+import { derivePathPlaceholderPairs, renamePathPlaceholder } from "../lib/pathPlaceholders";
 import { prepareImportQuerystring } from "../lib/prepareImportQuerystring";
 import { resolvedModelName } from "../lib/resolvedModelName";
 import { CountBadge } from "./core/CountBadge";
@@ -29,7 +28,6 @@ import type { GenericCompletionConfig } from "./core/Editor/genericCompletion";
 import { getUrlCompletionConfig } from "./core/Editor/url/completion";
 import { Editor } from "./core/Editor/LazyEditor";
 import { IconButton } from "./core/IconButton";
-import type { Pair } from "./core/PairEditor";
 import { PlainInput } from "./core/PlainInput";
 import type { TabItem, TabsRef } from "./core/Tabs/Tabs";
 import { setActiveTab, TabContent, Tabs } from "./core/Tabs/Tabs";
@@ -84,20 +82,33 @@ export function WebsocketRequestPane({ style, fullHeight, className, activeReque
     [],
   );
 
-  const { urlParameterPairs, urlParametersKey } = useMemo(() => {
-    const placeholderNames = extractPathPlaceholders(activeRequest.url);
-    const nonEmptyParameters = activeRequest.urlParameters.filter((p) => p.name || p.value);
-    const items: Pair[] = [...nonEmptyParameters];
-    for (const name of placeholderNames) {
-      const item = items.find((p) => p.name === name);
-      if (item) {
-        item.readOnlyName = true;
-      } else {
-        items.push({ name, value: "", enabled: true, readOnlyName: true, id: generateId() });
-      }
-    }
-    return { urlParameterPairs: items, urlParametersKey: placeholderNames.join(",") };
-  }, [activeRequest.url, activeRequest.urlParameters]);
+  // Renaming a path placeholder has to rewrite the URL and rename the parameter together, or the
+  // value detaches from the placeholder.
+  // NOTE: Reads the request fresh rather than closing over `activeRequest`. The row that calls this
+  //  holds onto it until the URL's placeholders change, so a captured request would go stale and
+  //  patch its parameter list back over newer edits.
+  const handleRenamePathPlaceholder = useCallback(
+    (oldName: string, newName: string) => {
+      const request = getModel("websocket_request", activeRequestId);
+      if (request == null) return false;
+
+      const patch = renamePathPlaceholder(request, oldName, newName);
+      if (patch == null) return false; // Unusable name, so the editor reverts the field
+      void patchModel(request, patch);
+      return true;
+    },
+    [activeRequestId],
+  );
+
+  const { urlParameterPairs, urlParametersKey } = useMemo(
+    () =>
+      derivePathPlaceholderPairs(
+        activeRequest.url,
+        activeRequest.urlParameters,
+        handleRenamePathPlaceholder,
+      ),
+    [activeRequest.url, activeRequest.urlParameters, handleRenamePathPlaceholder],
+  );
 
   const tabs = useMemo<TabItem[]>(() => {
     return [

apps/yaak-client/components/core/PairEditor.tsx

@@ -36,10 +36,19 @@ import type { RadioDropdownItem } from "./RadioDropdown";
 import { RadioDropdown } from "./RadioDropdown";
 
 export interface PairEditorHandle {
+  /**
+   * Focus a row's name field once it's able to take focus. Focus can't land immediately when the
+   * row isn't mounted yet or the editor is hidden — eg. sitting in a tab that's still becoming
+   * active — so this retries for up to ~1s. A newer focus request cancels a pending one.
+   */
   focusName(id: string): void;
+  /** Focus a row's value field. See {@link PairEditorHandle.focusName} for timing. */
   focusValue(id: string): void;
 }
 
+/** ~1s at 60fps, plenty for a tab switch to land without spinning forever if it never does */
+const MAX_FOCUS_ATTEMPTS = 60;
+
 export type PairEditorProps = {
   allowFileValues?: boolean;
   allowMultilineValues?: boolean;
@@ -53,7 +62,7 @@ export type PairEditorProps = {
   nameValidate?: InputProps["validate"];
   noScroll?: boolean;
   onChange: (pairs: PairWithId[]) => void;
-  pairs: Pair[];
+  pairs: EditablePair[];
   stateKey: InputProps["stateKey"];
   setRef?: (n: PairEditorHandle) => void;
   valueAutocomplete?: (name: string) => GenericCompletionConfig | undefined;
@@ -72,13 +81,35 @@ export type Pair = {
   contentType?: string;
   filename?: string;
   isFile?: boolean;
-  readOnlyName?: boolean;
 };
 
 export type PairWithId = Pair & {
   id: string;
 };
 
+/**
+ * A pair as handed to the editor. Adds behaviour that only the editor cares about, so the plain
+ * `Pair` stays the shape that gets written to models.
+ */
+export type EditablePair = Pair & {
+  /**
+   * When set, name edits are held until the field blurs and then committed through this, instead
+   * of calling `onChange` on every keystroke. Return false to reject the new name, which reverts
+   * the field. For names that can't be written directly, like a URL path placeholder that lives
+   * in the URL itself.
+   */
+  commitName?: (name: string) => boolean;
+};
+
+type EditablePairWithId = EditablePair & {
+  id: string;
+};
+
+/** Strip the editor-only fields, so they can never reach a model write */
+function toPairData({ commitName: _commitName, ...pair }: EditablePairWithId): PairWithId {
+  return pair;
+}
+
 /** Max number of pairs to show before prompting the user to reveal the rest */
 const MAX_INITIAL_PAIRS = 30;
 
@@ -106,8 +137,8 @@ export function PairEditor({
   setRef,
 }: PairEditorProps) {
   const [hoveredIndex, setHoveredIndex] = useState<number | null>(null);
-  const [isDragging, setIsDragging] = useState<PairWithId | null>(null);
-  const [pairs, setPairs] = useState<PairWithId[]>([]);
+  const [isDragging, setIsDragging] = useState<EditablePairWithId | null>(null);
+  const [pairs, setPairs] = useState<EditablePairWithId[]>([]);
   const [showAll, toggleShowAll] = useToggle(false);
   // NOTE: Use local force update key because we trigger an effect on forceUpdateKey change. If
   //  we simply pass forceUpdateKey to the editor, the data set by useEffect will be stale.
@@ -115,16 +146,38 @@ export function PairEditor({
 
   const rowsRef = useRef<Record<string, RowHandle | null>>({});
 
+  const pendingFocusFrame = useRef<number | null>(null);
+  useEffect(
+    () => () => {
+      if (pendingFocusFrame.current != null) cancelAnimationFrame(pendingFocusFrame.current);
+    },
+    [],
+  );
+
+  const focusWhenReady = useCallback((id: string, field: "name" | "value") => {
+    if (pendingFocusFrame.current != null) cancelAnimationFrame(pendingFocusFrame.current);
+
+    let attemptsLeft = MAX_FOCUS_ATTEMPTS;
+    const attempt = () => {
+      pendingFocusFrame.current = null;
+      const row = rowsRef.current[id];
+      const landed = field === "name" ? row?.focusName() : row?.focusValue();
+      if (landed || --attemptsLeft <= 0) return;
+      pendingFocusFrame.current = requestAnimationFrame(attempt);
+    };
+    attempt();
+  }, []);
+
   const handle = useMemo<PairEditorHandle>(
     () => ({
       focusName(id: string) {
-        rowsRef.current[id]?.focusName();
+        focusWhenReady(id, "name");
       },
       focusValue(id: string) {
-        rowsRef.current[id]?.focusValue();
+        focusWhenReady(id, "value");
       },
     }),
-    [],
+    [focusWhenReady],
   );
 
   const initPairEditorRow = useCallback(
@@ -147,7 +200,7 @@ export function PairEditor({
   // oxlint-disable-next-line react-hooks/exhaustive-deps -- Only care about forceUpdateKey
   useEffect(() => {
     // Remove empty headers on initial render and ensure they all have valid ids (pairs didn't use to have IDs)
-    const newPairs: PairWithId[] = [];
+    const newPairs: EditablePairWithId[] = [];
     for (let i = 0; i < originalPairs.length; i++) {
       const p = originalPairs[i];
       if (!p) continue; // Make TS happy
@@ -155,6 +208,21 @@ export function PairEditor({
       newPairs.push(ensurePairId(p));
     }
 
+    // When the reset holds the exact same rows (eg. renaming a URL path placeholder, which keeps
+    // every row id), swap the data in without rebuilding the row editors. Unfocused inputs re-seed
+    // themselves when `defaultValue` changes, and a rebuild would drop the user's focus and
+    // selection — like tabbing from a placeholder's name into its value.
+    const trailingPair = pairs[pairs.length - 1];
+    const sameRows =
+      trailingPair != null &&
+      isPairEmpty(trailingPair) &&
+      pairs.length === newPairs.length + 1 &&
+      newPairs.every((p, i) => p.id === pairs[i]?.id);
+    if (sameRows) {
+      setPairs([...newPairs, trailingPair]);
+      return;
+    }
+
     // Add empty last pair if there is none
     const lastPair = newPairs[newPairs.length - 1];
     if (lastPair == null || !isPairEmpty(lastPair)) {
@@ -166,10 +234,10 @@ export function PairEditor({
   }, [forceUpdateKey]);
 
   const setPairsAndSave = useCallback(
-    (fn: (pairs: PairWithId[]) => PairWithId[]) => {
+    (fn: (pairs: EditablePairWithId[]) => EditablePairWithId[]) => {
       setPairs((oldPairs) => {
         const pairs = fn(oldPairs);
-        onChange(pairs);
+        onChange(pairs.map(toPairData));
         return pairs;
       });
     },
@@ -177,7 +245,7 @@ export function PairEditor({
   );
 
   const handleChange = useCallback(
-    (pair: PairWithId) =>
+    (pair: EditablePairWithId) =>
       setPairsAndSave((pairs) => pairs.map((p) => (pair.id !== p.id ? p : pair))),
     [setPairsAndSave],
   );
@@ -362,14 +430,14 @@ export function PairEditor({
 
 type PairEditorRowProps = {
   className?: string;
-  pair: PairWithId;
+  pair: EditablePairWithId;
   forceFocusNamePairId?: string | null;
   forceFocusValuePairId?: string | null;
-  onChange?: (pair: PairWithId) => void;
-  onDelete?: (pair: PairWithId, focusPrevious: boolean) => void;
-  onFocusName?: (pair: PairWithId) => void;
-  onFocusValue?: (pair: PairWithId) => void;
-  onSubmit?: (pair: PairWithId) => void;
+  onChange?: (pair: EditablePairWithId) => void;
+  onDelete?: (pair: EditablePairWithId, focusPrevious: boolean) => void;
+  onFocusName?: (pair: EditablePairWithId) => void;
+  onFocusValue?: (pair: EditablePairWithId) => void;
+  onSubmit?: (pair: EditablePairWithId) => void;
   isLast?: boolean;
   disabled?: boolean;
   disableDrag?: boolean;
@@ -397,8 +465,8 @@ type PairEditorRowProps = {
 >;
 
 interface RowHandle {
-  focusName(): void;
-  focusValue(): void;
+  focusName(): boolean;
+  focusValue(): boolean;
 }
 
 export function PairEditorRow({
@@ -436,9 +504,11 @@ export function PairEditorRow({
   const handle = useRef<RowHandle>({
     focusName() {
       nameInputRef.current?.focus();
+      return nameInputRef.current?.isFocused() ?? false;
     },
     focusValue() {
       valueInputRef.current?.focus();
+      return valueInputRef.current?.isFocused() ?? false;
     },
   });
 
@@ -471,11 +541,37 @@ export function PairEditorRow({
     [onChange, pair],
   );
 
+  // The name being typed into a deferred-commit field, before it's committed or reverted
+  const pendingName = useRef<string | null>(null);
+
   const handleChangeName = useMemo(
-    () => (name: string) => onChange?.({ ...pair, name }),
+    () => (name: string) => {
+      // Keep the edit local until commit. Writing on every keystroke would reset the editor from
+      // beneath the cursor, since the pairs are derived from the name being edited.
+      if (pair.commitName != null) pendingName.current = name;
+      else onChange?.({ ...pair, name });
+    },
     [onChange, pair],
   );
 
+  const revertName = useCallback(() => {
+    const nameInput = nameInputRef.current;
+    if (nameInput != null) {
+      const changes = { from: 0, to: nameInput.value().length, insert: pair.name };
+      nameInput.dispatch({ changes });
+    }
+    pendingName.current = null;
+  }, [pair.name]);
+
+  const handleBlurName = useCallback(() => {
+    if (pair.commitName == null) return;
+
+    const name = pendingName.current;
+    pendingName.current = null;
+    if (name == null || name === pair.name) return;
+    if (!pair.commitName(name)) revertName();
+  }, [pair, revertName]);
+
   const handleChangeValueText = useMemo(
     () => (value: string) => onChange?.({ ...pair, value, isFile: false }),
     [onChange, pair],
@@ -596,7 +692,7 @@ export function PairEditorRow({
           stateKey={`name.${pair.id}.${stateKey}`}
           disabled={disabled}
           wrapLines={false}
-          readOnly={pair.readOnlyName || isDraggingGlobal}
+          readOnly={isDraggingGlobal}
           size="sm"
           required={!isLast && !!pair.enabled && !!pair.value}
           validate={nameValidate}
@@ -606,6 +702,7 @@ export function PairEditorRow({
           defaultValue={pair.name}
           label="Name"
           name={`name[${index}]`}
+          onBlur={handleBlurName}
           onChange={handleChangeName}
           onFocus={handleFocusName}
           placeholder={namePlaceholder ?? "name"}
@@ -808,7 +905,7 @@ function FileActionsDropdown({
   );
 }
 
-function emptyPair(): PairWithId {
+function emptyPair(): EditablePairWithId {
   return ensurePairId({ enabled: true, name: "", value: "" });
 }
 

apps/yaak-client/components/core/PairEditor.util.tsx

@@ -1,9 +1,10 @@
 import { generateId } from "../../lib/generateId";
 import type { Pair, PairWithId } from "./PairEditor";
 
-export function ensurePairId(p: Pair): PairWithId {
+// NOTE: Generic so callers keep whatever they passed in (eg. an EditablePair stays editable)
+export function ensurePairId<T extends Pair>(p: T): T & PairWithId {
   if (typeof p.id === "string") {
-    return p as PairWithId;
+    return p as T & PairWithId;
   }
   return { ...p, id: p.id ?? generateId() };
 }

apps/yaak-client/lib/pathPlaceholders.test.ts

@@ -1,5 +1,9 @@
 import { describe, expect, test } from "vite-plus/test";
-import { extractPathPlaceholders } from "./pathPlaceholders";
+import {
+  derivePathPlaceholderPairs,
+  extractPathPlaceholders,
+  renamePathPlaceholder,
+} from "./pathPlaceholders";
 
 describe("extractPathPlaceholders", () => {
   test("extracts a single placeholder", () => {
@@ -26,3 +30,185 @@ describe("extractPathPlaceholders", () => {
     expect(extractPathPlaceholders("https://example.com/foo/bar?q=1#hash")).toEqual([]);
   });
 });
+
+describe("derivePathPlaceholderPairs", () => {
+  const neverRename = () => false;
+
+  test("adds a row for a placeholder with no parameter", () => {
+    const { urlParameterPairs } = derivePathPlaceholderPairs("/users/:id", [], neverRename);
+    expect(urlParameterPairs).toMatchObject([{ name: ":id", value: "", enabled: true }]);
+    expect(urlParameterPairs[0]?.commitName).toBeTypeOf("function");
+  });
+
+  test("gives the existing parameter for a placeholder a commitName, without mutating it", () => {
+    const parameter = { name: ":id", value: "123", enabled: true, id: "p1" };
+    const { urlParameterPairs } = derivePathPlaceholderPairs(
+      "/users/:id",
+      [parameter],
+      neverRename,
+    );
+    expect(urlParameterPairs[0]).toMatchObject({ name: ":id", value: "123", id: "p1" });
+    expect(urlParameterPairs[0]?.commitName).toBeTypeOf("function");
+    expect(parameter).toEqual({ name: ":id", value: "123", enabled: true, id: "p1" });
+  });
+
+  test("leaves query parameters alone", () => {
+    const { urlParameterPairs } = derivePathPlaceholderPairs(
+      "/users/:id",
+      [{ name: "q", value: "hi", enabled: true, id: "p1" }],
+      neverRename,
+    );
+    expect(urlParameterPairs[0]).toEqual({ name: "q", value: "hi", enabled: true, id: "p1" });
+    expect(urlParameterPairs[1]?.commitName).toBeTypeOf("function");
+  });
+
+  test("commitName renames this row's placeholder", () => {
+    const renames: [string, string][] = [];
+    const { urlParameterPairs } = derivePathPlaceholderPairs(
+      "/a/:x/b/:y",
+      [],
+      (oldName, newName) => {
+        renames.push([oldName, newName]);
+        return true;
+      },
+    );
+    urlParameterPairs[1]?.commitName?.(":z");
+    expect(renames).toEqual([[":y", ":z"]]);
+  });
+
+  test("drops empty parameters", () => {
+    const { urlParameterPairs } = derivePathPlaceholderPairs(
+      "/users",
+      [
+        { name: "", value: "", enabled: true, id: "p1" },
+        { name: "q", value: "", enabled: true, id: "p2" },
+      ],
+      neverRename,
+    );
+    expect(urlParameterPairs).toMatchObject([{ name: "q", id: "p2" }]);
+  });
+
+  test("collapses a placeholder that appears twice into one row", () => {
+    const { urlParameterPairs } = derivePathPlaceholderPairs("/a/:id/b/:id", [], neverRename);
+    expect(urlParameterPairs).toMatchObject([{ name: ":id" }]);
+  });
+
+  test("gives a derived row the same id every time, so re-deriving is stable", () => {
+    const first = derivePathPlaceholderPairs("/users/:id", [], neverRename);
+    const second = derivePathPlaceholderPairs("/users/:id", [], neverRename);
+    expect(first.urlParameterPairs[0]?.id).toEqual(second.urlParameterPairs[0]?.id);
+  });
+
+  test("derived row ids avoid colliding with a persisted derived id", () => {
+    // A derived id sticks to the parameter once the user gives the row a value. If its placeholder
+    // is then renamed away in the URL bar, the parameter survives as a stray still holding the id,
+    // and the replacement placeholder's row must not collide with it.
+    const stray = { name: ":old", value: "42", enabled: true, id: "path-placeholder:0" };
+    const { urlParameterPairs } = derivePathPlaceholderPairs("/pets/:new", [stray], neverRename);
+    const ids = urlParameterPairs.map((p) => p.id);
+    expect(new Set(ids).size).toEqual(ids.length);
+  });
+
+  test("keeps a derived row's id stable across a rename", () => {
+    const before = derivePathPlaceholderPairs("/a/:x/b/:y", [], neverRename);
+    const after = derivePathPlaceholderPairs("/a/:x2/b/:y", [], neverRename);
+    expect(after.urlParameterPairs.map((p) => p.id)).toEqual(
+      before.urlParameterPairs.map((p) => p.id),
+    );
+  });
+
+  test("keys off the placeholder names", () => {
+    expect(derivePathPlaceholderPairs("/a/:x/b/:y", [], neverRename).urlParametersKey).toEqual(
+      ":x,:y",
+    );
+    expect(derivePathPlaceholderPairs("/a/b", [], neverRename).urlParametersKey).toEqual("");
+  });
+});
+
+describe("renamePathPlaceholder", () => {
+  const model = (url: string, urlParameters: { name: string; value: string }[] = []) => ({
+    url,
+    urlParameters,
+  });
+
+  test("renames the placeholder in the URL", () => {
+    expect(
+      renamePathPlaceholder(model("https://x.com/pets/:petId/info"), ":petId", ":animalId"),
+    ).toEqual({ url: "https://x.com/pets/:animalId/info", urlParameters: [] });
+  });
+
+  test("carries the parameter value over to the new name", () => {
+    const patch = renamePathPlaceholder(
+      model("/pets/:petId", [
+        { name: "q", value: "1" },
+        { name: ":petId", value: "42" },
+      ]),
+      ":petId",
+      ":animalId",
+    );
+    expect(patch).toEqual({
+      url: "/pets/:animalId",
+      urlParameters: [
+        { name: "q", value: "1" },
+        { name: ":animalId", value: "42" },
+      ],
+    });
+  });
+
+  test("renames every occurrence of a repeated placeholder", () => {
+    expect(renamePathPlaceholder(model("/a/:id/b/:id"), ":id", ":key")?.url).toEqual(
+      "/a/:key/b/:key",
+    );
+  });
+
+  test("adds a missing leading colon", () => {
+    expect(renamePathPlaceholder(model("/pets/:petId"), ":petId", "animalId")?.url).toEqual(
+      "/pets/:animalId",
+    );
+  });
+
+  test("renames a placeholder followed by a literal colon", () => {
+    expect(renamePathPlaceholder(model("/tasks/:id:cancel"), ":id", ":taskId")?.url).toEqual(
+      "/tasks/:taskId:cancel",
+    );
+  });
+
+  test("does not rename a placeholder the new name is a prefix of", () => {
+    expect(renamePathPlaceholder(model("/a/:id/b/:idx"), ":id", ":key")?.url).toEqual(
+      "/a/:key/b/:idx",
+    );
+  });
+
+  test("does not touch a same-named segment that isn't a placeholder", () => {
+    expect(renamePathPlaceholder(model("/id/:id?x=:id"), ":id", ":key")?.url).toEqual(
+      "/id/:key?x=:id",
+    );
+  });
+
+  test("treats regex characters in the old name literally", () => {
+    expect(renamePathPlaceholder(model("/a/:i.d/b/:iXd"), ":i.d", ":key")?.url).toEqual(
+      "/a/:key/b/:iXd",
+    );
+  });
+
+  test.each([[""], [":"], [":a/b"], [":a?b"], [":a#b"], [":a:b"], [":a b"], [":a\tb"]])(
+    "rejects the unusable name %j",
+    (name) => {
+      expect(renamePathPlaceholder(model("/pets/:petId"), ":petId", name)).toBeNull();
+    },
+  );
+
+  test("rejects a name already used by another placeholder", () => {
+    expect(renamePathPlaceholder(model("/pets/:petId/:ownerId"), ":petId", ":ownerId")).toBeNull();
+  });
+
+  test("allows renaming a placeholder to itself", () => {
+    expect(renamePathPlaceholder(model("/pets/:petId"), ":petId", ":petId")?.url).toEqual(
+      "/pets/:petId",
+    );
+  });
+
+  test("rejects renaming a placeholder that isn't in the URL", () => {
+    expect(renamePathPlaceholder(model("/pets/:petId"), ":other", ":animalId")).toBeNull();
+  });
+});

apps/yaak-client/lib/pathPlaceholders.ts

@@ -1,3 +1,6 @@
+import type { HttpUrlParameter } from "@yaakapp-internal/models";
+import type { EditablePair } from "../components/core/PairEditor";
+
 /**
  * Extract `:name`-style path placeholders from a URL string.
  *
@@ -12,3 +15,88 @@
 export function extractPathPlaceholders(url: string): string[] {
   return Array.from(url.matchAll(/\/(:[^/?#:]+)/g)).map((m) => m[1] ?? "");
 }
+
+/**
+ * Build the rows for the Params tab: the request's URL parameters, plus a row for each path
+ * placeholder in the URL that doesn't have one yet. A placeholder that appears more than once
+ * in the URL still gets a single row.
+ *
+ * Only placeholder rows get a `commitName`, which makes the editor hold name edits until blur and
+ * hand them to `renamePlaceholder` instead of writing on every keystroke — renaming has to rewrite
+ * the URL too. `renamePlaceholder` returns false to reject the new name, which reverts the field.
+ *
+ * `urlParametersKey` changes whenever the URL's placeholders do, and is used to reset the pair
+ * editor so derived rows appear and disappear along with the URL.
+ */
+export function derivePathPlaceholderPairs(
+  url: string,
+  urlParameters: HttpUrlParameter[],
+  renamePlaceholder: (oldName: string, newName: string) => boolean,
+): { urlParameterPairs: EditablePair[]; urlParametersKey: string } {
+  const placeholderNames = extractPathPlaceholders(url);
+  const commitNameFor = (oldName: string) => (newName: string) =>
+    renamePlaceholder(oldName, newName);
+
+  // NOTE: Copy each parameter because `commitName` is UI-only. Adding it in place would mutate the
+  //  persisted model.
+  const urlParameterPairs: EditablePair[] = urlParameters
+    .filter((p) => p.name || p.value)
+    .map((p) =>
+      placeholderNames.includes(p.name) ? { ...p, commitName: commitNameFor(p.name) } : { ...p },
+    );
+
+  // NOTE: Ids are derived from the placeholder's position instead of generated, so neither
+  //  re-deriving nor renaming hands a row a new identity. The pair editor keys rows by id, so a
+  //  changed id remounts the row and drops the user's focus.
+  //
+  //  A derived id sticks to the parameter once the user gives the row a value, so a parameter that
+  //  outlives its placeholder (renamed away in the URL bar) still holds one. Skip past taken ids
+  //  so a new placeholder at that position can't collide with it.
+  const takenIds = new Set(urlParameterPairs.map((p) => p.id));
+  const uniquePlaceholderNames = [...new Set(placeholderNames)];
+  for (const [index, name] of uniquePlaceholderNames.entries()) {
+    if (urlParameterPairs.some((p) => p.name === name)) continue;
+
+    let id = `path-placeholder:${index}`;
+    for (let bump = index + 1; takenIds.has(id); bump++) id = `path-placeholder:${bump}`;
+    takenIds.add(id);
+
+    urlParameterPairs.push({ name, value: "", enabled: true, commitName: commitNameFor(name), id });
+  }
+
+  return { urlParameterPairs, urlParametersKey: placeholderNames.join(",") };
+}
+
+/**
+ * Compute the patch for renaming a path placeholder: every occurrence replaced in the URL, and
+ * the matching URL parameter renamed so the user's value follows along. Both have to be applied
+ * together, or the value detaches from the placeholder.
+ *
+ * Returns `null` when the rename can't be applied, meaning the caller should leave the model
+ * alone. That's the case when the new name wouldn't parse as a placeholder anymore (empty, or
+ * containing `/`, `?`, `#`, `:`, or whitespace) or when it's already used by another placeholder
+ * in the URL. A missing leading `:` is added rather than rejected, since focusing the name field
+ * selects all of its text and typing over it is the natural way to rename.
+ */
+export function renamePathPlaceholder(
+  model: { url: string; urlParameters: HttpUrlParameter[] },
+  oldName: string,
+  newName: string,
+): { url: string; urlParameters: HttpUrlParameter[] } | null {
+  const name = newName.startsWith(":") ? newName : `:${newName}`;
+  if (!/^:[^/?#:\s]+$/.test(name)) return null;
+
+  const placeholderNames = extractPathPlaceholders(model.url);
+  if (!placeholderNames.includes(oldName)) return null;
+  if (name !== oldName && placeholderNames.includes(name)) return null;
+
+  const pattern = new RegExp(`(/)${escapeRegExp(oldName)}(?=[/?#:]|$)`, "g");
+  return {
+    url: model.url.replace(pattern, (_match, slash: string) => `${slash}${name}`),
+    urlParameters: model.urlParameters.map((p) => (p.name === oldName ? { ...p, name } : p)),
+  };
+}
+
+function escapeRegExp(text: string): string {
+  return text.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}