Lspwhy explains the last language server query asked, its kind, argument and place, not always a definition at the cursor

Lspwhy said it explains how the last request was answered, but it always
replayed a definition query at the current cursor. So after a failed Hover
it narrated a gd somewhere else, which told nothing about the failure.
Now the core remembers the last query (kind, argument, pane, offset), and
Lspwhy sends it as `<kind> <arg>`, at the query's offset when asked from
the same pane. The client narrates that kind: lsp.explaining reads it, and
the heading names it ("the hover query at byte N"). With nothing asked yet
it is a definition, as before. The effect's arg grows to 160 bytes so a
128-byte argument fits with its kind.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 26 insertions, 0 deletions

diff --git a/src/lsp/lsp.zig b/src/lsp/lsp.zig
index 43f94f95..33e95570 100644
--- a/src/lsp/lsp.zig
+++ b/src/lsp/lsp.zig
@@ -31,8 +31,34 @@ pub const Req = struct {
     offset: u32,
     arg: []const u8 = "",
     root: []const u8 = "",
+    /// For `explain`: the query it narrates, read from `arg` (`<kind>
+    /// <arg>`) by `explaining`; a definition when none was asked before.
+    explains: Kind = .definition,
 };
 
+/// An `explain` request made the one it narrates: `explains` and `arg` set
+/// from its `<kind> <arg>`; any other request as it is.
+pub fn explaining(req: Req) Req {
+    if (req.kind != .explain) return req;
+    var r = req;
+    const sp = std.mem.indexOfScalar(u8, req.arg, ' ') orelse req.arg.len;
+    const named = std.meta.stringToEnum(Kind, req.arg[0..sp]) orelse .definition;
+    r.explains = if (named == .explain or named == .status) .definition else named;
+    r.arg = if (sp < req.arg.len) req.arg[sp + 1 ..] else "";
+    return r;
+}
+
+test "an explain request narrates the query named in its arg, a definition by default" {
+    const base: Req = .{ .kind = .explain, .path = "/x.zig", .source = "", .offset = 0 };
+    var r = base;
+    r.arg = "hover ";
+    try std.testing.expectEqual(Kind.hover, explaining(r).explains);
+    r.arg = "rename newName";
+    try std.testing.expectEqual(Kind.rename, explaining(r).explains);
+    try std.testing.expectEqualStrings("newName", explaining(r).arg);
+    try std.testing.expectEqual(Kind.definition, explaining(base).explains);
+}
+
 /// Every language, Zig's (zls) included, through the protocol client, which
 /// runs its server as a child process. None on the web or the board.
 const backends = if (@import("pardes_config").platform == .web or @import("pardes_config").platform == .esp32p4)