perf(mcp): prefilter scoped search_code filelist by path_filter

src/mcp/mcp.c

@@ -4435,9 +4435,19 @@ static void classify_all_grep_hits(grep_match_t *gm, int gm_count, cbm_store_t *
     }
 }
 
-/* Write indexed file list for scoped grep. Returns true if scoped. */
+/* Write indexed file list for scoped grep. Returns true if scoped.
+ * When a path_filter is provided, apply it here — before grep — so large
+ * indexed projects do not scan files only for collect_grep_matches to discard
+ * them later. The predicate is IDENTICAL to the post-grep filter: the same
+ * compiled regex run against the same root-relative path (separators
+ * normalized on Windows first), so prefiltering can only skip files whose
+ * hits would be dropped anyway — results-preserving by construction.
+ * *out_written receives the number of records written (0 = the filter
+ * excluded every indexed file). */
 static bool write_scoped_filelist(cbm_mcp_server_t *srv, const char *project, const char *root_path,
-                                  const char *filelist) {
+                                  const char *filelist, bool has_path_filter,
+                                  cbm_regex_t *path_regex, int *out_written) {
+    *out_written = 0;
     cbm_store_t *pre_store = resolve_store(srv, project);
     if (!pre_store) {
         return false;
@@ -4450,8 +4460,17 @@ static bool write_scoped_filelist(cbm_mcp_server_t *srv, const char *project, co
     }
     FILE *fl = fopen(filelist, "wb");
     bool ok = false;
+    int written = 0;
     if (fl) {
         for (int fi = 0; fi < indexed_count; fi++) {
+            if (has_path_filter && path_regex) {
+#ifdef _WIN32
+                cbm_normalize_path_sep(indexed_files[fi]);
+#endif
+                if (cbm_regexec(path_regex, indexed_files[fi], 0, NULL, 0) != CBM_REG_OK) {
+                    continue;
+                }
+            }
             /* Write "<root>/<file>" piece-by-piece (no fixed-size buffer, so an
              * arbitrarily long absolute path cannot overflow). Forward slash join
              * so xargs doesn't treat Windows backslashes as escapes; binary mode
@@ -4468,6 +4487,7 @@ static bool write_scoped_filelist(cbm_mcp_server_t *srv, const char *project, co
 #else
             (void)fputc('\0', fl);
 #endif
+            written++;
         }
         (void)fclose(fl);
         ok = true;
@@ -4476,6 +4496,7 @@ static bool write_scoped_filelist(cbm_mcp_server_t *srv, const char *project, co
         free(indexed_files[fi]);
     }
     free(indexed_files);
+    *out_written = written;
     return ok;
 }
 
@@ -4699,33 +4720,47 @@ static char *handle_search_code(cbm_mcp_server_t *srv, const char *args) {
     char filelist[CBM_SZ_256];
     snprintf(filelist, sizeof(filelist), "%s.files", tmpfile);
     bool scoped = false;
+    int scoped_written = 0;
 
-    scoped = write_scoped_filelist(srv, project, root_path, filelist);
+    scoped = write_scoped_filelist(srv, project, root_path, filelist, has_path_filter,
+                                   has_path_filter ? &path_regex : NULL, &scoped_written);
 
-    char cmd[CBM_SZ_4K];
-    build_grep_cmd(cmd, sizeof(cmd), use_regex, scoped, file_pattern, tmpfile, filelist, root_path);
+    /* Collect grep matches into array */
+    int gm_count = 0;
+    grep_match_t *gm = NULL;
+    if (scoped && scoped_written == 0) {
+        /* The path_filter excluded every indexed file — nothing to scan.
+         * Skip the grep subprocess: xargs on an empty filelist is
+         * platform-dependent (GNU execs grep once with no operands, BSD
+         * skips), and the post-grep filter would drop every hit anyway. */
+        gm = malloc(sizeof(grep_match_t)); /* empty set; freed below */
+        cbm_unlink(tmpfile);
+        cbm_unlink(filelist);
+    } else {
+        char cmd[CBM_SZ_4K];
+        build_grep_cmd(cmd, sizeof(cmd), use_regex, scoped, file_pattern, tmpfile, filelist,
+                       root_path);
+
+        FILE *fp = cbm_popen(cmd, "r");
+        if (!fp) {
+            cbm_unlink(tmpfile);
+            if (scoped) {
+                cbm_unlink(filelist);
+            }
+            free(root_path);
+            free(pattern);
+            free(project);
+            free(file_pattern);
+            return cbm_mcp_text_result("search failed", true);
+        }
 
-    FILE *fp = cbm_popen(cmd, "r");
-    if (!fp) {
+        gm = collect_grep_matches(fp, root_path, strlen(root_path), has_path_filter, &path_regex,
+                                  grep_limit, &gm_count);
+        cbm_pclose(fp);
         cbm_unlink(tmpfile);
         if (scoped) {
             cbm_unlink(filelist);
         }
-        free(root_path);
-        free(pattern);
-        free(project);
-        free(file_pattern);
-        return cbm_mcp_text_result("search failed", true);
-    }
-
-    /* Collect grep matches into array */
-    int gm_count = 0;
-    grep_match_t *gm = collect_grep_matches(fp, root_path, strlen(root_path), has_path_filter,
-                                            &path_regex, grep_limit, &gm_count);
-    cbm_pclose(fp);
-    cbm_unlink(tmpfile);
-    if (scoped) {
-        cbm_unlink(filelist);
     }
 
     /* ── Phase 2+3: Block expansion + graph ranking ──────────── */

tests/test_mcp.c

@@ -1493,6 +1493,166 @@ TEST(search_code_scoped_path_with_spaces_issue687) {
     PASS();
 }
 
+/* Shared fixture for the path_filter prefilter tests (PR #756 distilled):
+ * a project with two indexed files that both contain the search pattern —
+ * src/handler.go (inside the filter) and vendor/other.go (outside it). */
+static cbm_mcp_server_t *setup_prefilter_server(char *tmp, size_t tmp_sz, char *src_path,
+                                                size_t src_sz, char *vendor_path, size_t vendor_sz) {
+    snprintf(tmp, tmp_sz, "/tmp/cbm_srch_pref_XXXXXX");
+    if (!cbm_mkdtemp(tmp)) {
+        return NULL;
+    }
+    char dir[640];
+    snprintf(dir, sizeof(dir), "%s/src", tmp);
+    cbm_mkdir(dir);
+    snprintf(dir, sizeof(dir), "%s/vendor", tmp);
+    cbm_mkdir(dir);
+
+    snprintf(src_path, src_sz, "%s/src/handler.go", tmp);
+    snprintf(vendor_path, vendor_sz, "%s/vendor/other.go", tmp);
+    FILE *fp = fopen(src_path, "w");
+    if (!fp) {
+        return NULL;
+    }
+    fprintf(fp, "package main\n\nfunc HandleRequest() error {\n\treturn nil\n}\n");
+    fclose(fp);
+    fp = fopen(vendor_path, "w");
+    if (!fp) {
+        return NULL;
+    }
+    fprintf(fp, "package vendored\n\nfunc HandleRequest() error {\n\treturn nil\n}\n");
+    fclose(fp);
+
+    cbm_mcp_server_t *srv = cbm_mcp_server_new(NULL);
+    if (!srv) {
+        return NULL;
+    }
+    cbm_store_t *st = cbm_mcp_server_store(srv);
+    const char *proj = "prefilter-search";
+    cbm_mcp_server_set_project(srv, proj);
+    cbm_store_upsert_project(st, proj, tmp);
+
+    cbm_node_t n1 = {.project = proj,
+                     .label = "Function",
+                     .name = "HandleRequest",
+                     .qualified_name = "prefilter-search.main.HandleRequest",
+                     .file_path = "src/handler.go",
+                     .start_line = 3,
+                     .end_line = 5};
+    cbm_node_t n2 = {.project = proj,
+                     .label = "Function",
+                     .name = "HandleRequest",
+                     .qualified_name = "prefilter-search.vendored.HandleRequest",
+                     .file_path = "vendor/other.go",
+                     .start_line = 3,
+                     .end_line = 5};
+    if (cbm_store_upsert_node(st, &n1) <= 0 || cbm_store_upsert_node(st, &n2) <= 0) {
+        cbm_mcp_server_free(srv);
+        return NULL;
+    }
+    return srv;
+}
+
+static void cleanup_prefilter_dir(const char *tmp, const char *src_path, const char *vendor_path) {
+    char dir[640];
+    unlink(src_path);
+    unlink(vendor_path);
+    snprintf(dir, sizeof(dir), "%s/src", tmp);
+    rmdir(dir);
+    snprintf(dir, sizeof(dir), "%s/vendor", tmp);
+    rmdir(dir);
+    rmdir(tmp);
+}
+
+/* PR #756 (distilled): scoped search_code prefilters the indexed filelist by
+ * path_filter before grep runs. POSITIVE invariant guard: a path_filter that
+ * matches the file containing the hit must still return that hit (guards
+ * against over-filtering — the prefilter predicate must stay IDENTICAL to the
+ * post-grep filter in collect_grep_matches), and files outside the filter
+ * stay excluded. Green on pre-prefilter main too (the post-grep filter alone
+ * produced the same results): the change is results-preserving perf-only. */
+TEST(search_code_path_filter_prefilter_keeps_matches) {
+    char tmp[512], src_path[768], vendor_path[768];
+    cbm_mcp_server_t *srv = setup_prefilter_server(tmp, sizeof(tmp), src_path, sizeof(src_path),
+                                                   vendor_path, sizeof(vendor_path));
+    ASSERT_NOT_NULL(srv);
+
+    char *resp = cbm_mcp_server_handle(
+        srv, "{\"jsonrpc\":\"2.0\",\"id\":95,\"method\":\"tools/call\","
+             "\"params\":{\"name\":\"search_code\","
+             "\"arguments\":{\"pattern\":\"HandleRequest\",\"project\":\"prefilter-search\","
+             "\"path_filter\":\"^src/\"}}}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_TRUE(strstr(resp, "\"isError\":true") == NULL);
+    char *inner = extract_text_content(resp);
+    ASSERT_NOT_NULL(inner);
+
+    /* The in-filter hit is returned; the out-of-filter file is not. */
+    ASSERT_NOT_NULL(strstr(inner, "src/handler.go"));
+    ASSERT_TRUE(strstr(inner, "vendor/other.go") == NULL);
+
+    /* Exactly the one in-filter grep match survives (same count before and
+     * after the prefilter — predicate identity). */
+    int grep_matches = -1;
+    const char *g = strstr(inner, "\"total_grep_matches\":");
+    if (g) {
+        sscanf(g, "\"total_grep_matches\":%d", &grep_matches);
+    }
+    ASSERT_EQ(grep_matches, 1);
+
+    free(inner);
+    free(resp);
+    cbm_mcp_server_free(srv);
+    cleanup_prefilter_dir(tmp, src_path, vendor_path);
+    PASS();
+}
+
+/* PR #756 (distilled): path_filter matching ZERO indexed files. With the
+ * prefilter the scoped filelist has 0 records, and handle_search_code now
+ * skips the grep subprocess entirely (xargs on an empty filelist is
+ * platform-dependent: GNU execs grep once with no operands, BSD skips) and
+ * returns the empty result directly. Must be a clean zero-result response —
+ * no error. Green on pre-prefilter main too (there the full filelist is
+ * grepped and the post-grep filter drops every hit — an empty filelist is
+ * unreachable on main): guards the edge the prefilter introduces. */
+TEST(search_code_path_filter_matches_nothing) {
+    char tmp[512], src_path[768], vendor_path[768];
+    cbm_mcp_server_t *srv = setup_prefilter_server(tmp, sizeof(tmp), src_path, sizeof(src_path),
+                                                   vendor_path, sizeof(vendor_path));
+    ASSERT_NOT_NULL(srv);
+
+    char *resp = cbm_mcp_server_handle(
+        srv, "{\"jsonrpc\":\"2.0\",\"id\":96,\"method\":\"tools/call\","
+             "\"params\":{\"name\":\"search_code\","
+             "\"arguments\":{\"pattern\":\"HandleRequest\",\"project\":\"prefilter-search\","
+             "\"path_filter\":\"^no_such_dir/\"}}}");
+    ASSERT_NOT_NULL(resp);
+    ASSERT_TRUE(strstr(resp, "\"isError\":true") == NULL);
+    char *inner = extract_text_content(resp);
+    ASSERT_NOT_NULL(inner);
+
+    int grep_matches = -1;
+    const char *g = strstr(inner, "\"total_grep_matches\":");
+    if (g) {
+        sscanf(g, "\"total_grep_matches\":%d", &grep_matches);
+    }
+    ASSERT_EQ(grep_matches, 0);
+    int results = -1;
+    const char *r = strstr(inner, "\"total_results\":");
+    if (r) {
+        sscanf(r, "\"total_results\":%d", &results);
+    }
+    ASSERT_EQ(results, 0);
+    ASSERT_TRUE(strstr(inner, "handler.go") == NULL);
+    ASSERT_TRUE(strstr(inner, "other.go") == NULL);
+
+    free(inner);
+    free(resp);
+    cbm_mcp_server_free(srv);
+    cleanup_prefilter_dir(tmp, src_path, vendor_path);
+    PASS();
+}
+
 /* issue #283: search_code with regex=true and a syntactically invalid pattern
  * must return an explicit error, not an empty result indistinguishable from a
  * legitimate no-match. */
@@ -3810,6 +3970,8 @@ SUITE(mcp) {
     RUN_TEST(tool_search_code_no_project);
     RUN_TEST(search_code_multi_word);
     RUN_TEST(search_code_scoped_path_with_spaces_issue687);
+    RUN_TEST(search_code_path_filter_prefilter_keeps_matches);
+    RUN_TEST(search_code_path_filter_matches_nothing);
     RUN_TEST(search_code_invalid_regex_errors_issue283);
     RUN_TEST(search_code_literal_pipe_warns_issue282);
     RUN_TEST(search_code_ampersand_accepted_issue272);