fix: point selector warning LOCs at the actual selector line

findSelectorLineOffset only handled descendant (`& `) and child
(`& > `) combinator prefixes when stripping Stylis-normalized
selectors to search for them in the raw CSS. Sibling combinators
(`& +`, `& ~`) were not handled, so warnings for selectors like
`& + span` or `& ~ div` always pointed at the template literal
start (line offset 0) instead of the selector's actual line.

Extend the combinator strip regex from `^&\s*>\s*` to
`^&\s*[>+~]\s*` and broaden the search prefix to also match
combinator characters preceding the tag name in the raw CSS.

Co-authored-by: Kenneth Skovhus <skovhus@users.noreply.github.com>

Author: cursoragent

src/__tests__/css-ir.test.ts

@@ -193,6 +193,42 @@ describe("findSelectorLineOffset", () => {
   }`;
     expect(findSelectorLineOffset(css, "& > button")).toBe(2);
   });
+
+  it("finds adjacent sibling selectors (Stylis '&+span' → raw '+ span {')", () => {
+    const css = `color: red;
+
+  & + span {
+    margin-left: 8px;
+  }`;
+    expect(findSelectorLineOffset(css, "&+span")).toBe(2);
+  });
+
+  it("finds general sibling selectors (Stylis '&~div' → raw '~ div {')", () => {
+    const css = `color: red;
+
+  & ~ div {
+    opacity: 0.5;
+  }`;
+    expect(findSelectorLineOffset(css, "&~div")).toBe(2);
+  });
+
+  it("finds sibling selectors written without & (Stylis '&+span' → raw '+ span {')", () => {
+    const css = `color: red;
+
+  + span {
+    margin-left: 8px;
+  }`;
+    expect(findSelectorLineOffset(css, "&+span")).toBe(2);
+  });
+
+  it("finds child combinator with Stylis-normalized spaces (Stylis '&>button' → raw '> button {')", () => {
+    const css = `color: red;
+
+  > button {
+    opacity: 0.5;
+  }`;
+    expect(findSelectorLineOffset(css, "&>button")).toBe(2);
+  });
 });
 
 /** Helper to create a minimal slot for testing (expression is unused by the IR). */

src/__tests__/transform.test.ts

@@ -607,6 +607,66 @@ export const App = () => <Container />;
     expect(typeof warning.loc?.column).toBe("number");
   });
 
+  it("should warn with correct line number for sibling combinator selector", () => {
+    const source = `
+import styled from 'styled-components';
+
+const Box = styled.div\`
+  color: red;
+
+  & + span {
+    margin-left: 8px;
+  }
+\`;
+
+export const App = () => <Box />;
+`;
+
+    const result = transformWithWarnings(
+      { source, path: "test.tsx" },
+      { jscodeshift: j, j, stats: () => {}, report: () => {} },
+      { adapter: fixtureAdapter },
+    );
+
+    expect(result.code).toBeNull();
+    const warning = result.warnings.find(
+      (w) => w.type === "Unsupported selector: sibling combinator",
+    );
+    expect(warning).toBeDefined();
+    // Line 4 is template start, `& + span` is on line 7 (3 lines into template content)
+    expect(warning?.loc?.line).toBe(7);
+  });
+
+  it("should warn with correct line number for descendant/child/sibling selector", () => {
+    const source = `
+import styled from 'styled-components';
+
+const Box = styled.div\`
+  color: red;
+
+  a {
+    text-decoration: none;
+  }
+\`;
+
+export const App = () => <Box><span /></Box>;
+`;
+
+    const result = transformWithWarnings(
+      { source, path: "test.tsx" },
+      { jscodeshift: j, j, stats: () => {}, report: () => {} },
+      { adapter: fixtureAdapter },
+    );
+
+    expect(result.code).toBeNull();
+    const warning = result.warnings.find(
+      (w) => w.type === "Unsupported selector: descendant/child/sibling selector",
+    );
+    expect(warning).toBeDefined();
+    // Line 4 is template start, `a {` is on line 7 (3 lines into template content)
+    expect(warning?.loc?.line).toBe(7);
+  });
+
   it("should emit info warning for & + & (adjacent sibling broadens to general)", () => {
     const source = `
 import styled from "styled-components";

src/internal/css-ir.ts

@@ -634,11 +634,15 @@ export function findSelectorLineOffset(rawCss: string, selector: string): number
     }
   }
 
-  // For element selectors: Stylis produces "& svg" from "svg { ... }".
-  // Strip the "& " prefix and search for the tag name followed by whitespace or {.
-  const stripped = selector.replace(/^&\s+/, "").replace(/^&\s*>\s*/, "");
+  // For element/combinator selectors: Stylis produces "& svg" from "svg { ... }",
+  // "&>button" from "> button { ... }", "&+span" from "+ span { ... }", etc.
+  // Strip the "& " prefix and any combinator (>, +, ~), then search for the
+  // remaining text followed by whitespace or {.
+  const stripped = selector.replace(/^&\s+/, "").replace(/^&\s*[>+~]\s*/, "");
   if (stripped !== selector) {
-    const tagMatch = rawCss.match(new RegExp(`(?:^|\\s)${escapeRegExp(stripped)}\\s*[{,]`, "m"));
+    const tagMatch = rawCss.match(
+      new RegExp(`(?:^|[\\s>+~])${escapeRegExp(stripped)}\\s*[{,]`, "m"),
+    );
     if (tagMatch) {
       return countNewlinesBefore(rawCss, tagMatch.index! + 1);
     }