feat(source): add mapping source for listing key mappings

Implements a new source that lists all Vim key mappings across different
modes. Shows mapping definitions, attributes (silent, noremap, etc.), and
supports filtering by mode and buffer-local status.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: lambdalisue

builtin/source/mapping.ts

@@ -0,0 +1,167 @@
+import * as fn from "@denops/std/function";
+
+import { defineSource, type Source } from "../../source.ts";
+
+type Detail = {
+  /**
+   * Mapping key/lhs
+   */
+  lhs: string;
+
+  /**
+   * Mapping value/rhs
+   */
+  rhs: string;
+
+  /**
+   * Mapping mode
+   */
+  mode: string;
+
+  /**
+   * Whether the mapping is buffer-local
+   */
+  bufferLocal: boolean;
+
+  /**
+   * Whether the mapping is silent
+   */
+  silent: boolean;
+
+  /**
+   * Whether the mapping is noremap
+   */
+  noremap: boolean;
+
+  /**
+   * Whether the mapping waits for more input
+   */
+  nowait: boolean;
+
+  /**
+   * Whether the mapping is an expression
+   */
+  expr: boolean;
+};
+
+export type MappingOptions = {
+  /**
+   * Which modes to include mappings from.
+   * Default includes all common modes.
+   * @default ["n", "i", "v", "x", "s", "o", "c", "t"]
+   */
+  modes?: string[];
+
+  /**
+   * Whether to include buffer-local mappings.
+   * @default true
+   */
+  includeBufferLocal?: boolean;
+
+  /**
+   * Whether to include plugin mappings (mappings containing <Plug>).
+   * @default false
+   */
+  includePluginMappings?: boolean;
+};
+
+/**
+ * Creates a Source that generates items from Vim key mappings.
+ *
+ * This Source retrieves all key mappings from specified modes and
+ * generates items for each one, showing their definitions and attributes.
+ *
+ * @param options - Options to customize mapping listing.
+ * @returns A Source that generates items representing mappings.
+ */
+export function mapping(
+  options: Readonly<MappingOptions> = {},
+): Source<Detail> {
+  const modes = options.modes ?? ["n", "i", "v", "x", "s", "o", "c", "t"];
+  const includeBufferLocal = options.includeBufferLocal ?? true;
+  const includePluginMappings = options.includePluginMappings ?? false;
+
+  return defineSource(async function* (denops, _params, { signal }) {
+    const items: Array<{
+      id: number;
+      value: string;
+      detail: Detail;
+    }> = [];
+
+    let id = 0;
+    for (const mode of modes) {
+      // Get mappings for this mode
+      const mappingList = await fn.maplist(denops, mode) as MappingInfo[];
+      signal?.throwIfAborted();
+
+      for (const mapping of mappingList) {
+        // Skip buffer-local mappings if not included
+        if (mapping.buffer && !includeBufferLocal) {
+          continue;
+        }
+
+        // Skip plugin mappings if not included
+        if (!includePluginMappings && mapping.rhs.includes("<Plug>")) {
+          continue;
+        }
+
+        // Build attributes
+        const attributes: string[] = [];
+        if (mapping.silent) attributes.push("silent");
+        if (mapping.noremap) attributes.push("noremap");
+        if (mapping.nowait) attributes.push("nowait");
+        if (mapping.expr) attributes.push("expr");
+        if (mapping.buffer) attributes.push("buffer");
+
+        // Format mode indicator
+        const modeIndicator = mode === "n" ? " " : `[${mode}]`;
+
+        // Format display value
+        const attrStr = attributes.length > 0
+          ? ` (${attributes.join(", ")})`
+          : "";
+        const truncatedRhs = mapping.rhs.length > 50
+          ? mapping.rhs.substring(0, 47) + "..."
+          : mapping.rhs;
+
+        items.push({
+          id: id++,
+          value: `${modeIndicator} ${mapping.lhs}${attrStr} → ${truncatedRhs}`,
+          detail: {
+            lhs: mapping.lhs,
+            rhs: mapping.rhs,
+            mode: mode,
+            bufferLocal: mapping.buffer,
+            silent: mapping.silent,
+            noremap: mapping.noremap,
+            nowait: mapping.nowait,
+            expr: mapping.expr,
+          },
+        });
+      }
+    }
+
+    // Sort by mode and then by lhs
+    items.sort((a, b) => {
+      const modeCmp = a.detail.mode.localeCompare(b.detail.mode);
+      if (modeCmp !== 0) return modeCmp;
+      return a.detail.lhs.localeCompare(b.detail.lhs);
+    });
+
+    yield* items;
+  });
+}
+
+type MappingInfo = {
+  lhs: string;
+  rhs: string;
+  silent: boolean;
+  noremap: boolean;
+  nowait: boolean;
+  expr: boolean;
+  buffer: boolean;
+  mode: string;
+  sid: number;
+  lnum: number;
+  script: boolean;
+};

builtin/source/mod.ts

@@ -10,6 +10,7 @@ export * from "./jumplist.ts";
 export * from "./line.ts";
 export * from "./list.ts";
 export * from "./loclist.ts";
+export * from "./mapping.ts";
 export * from "./mark.ts";
 export * from "./noop.ts";
 export * from "./oldfiles.ts";