From 74c22372966bcd90fbe31d3c6f1188d01b1f57a7 Mon Sep 17 00:00:00 2001
From: Tim Stack <timothyshanestack@gmail.com>
Date: Tue, 16 Aug 2022 22:39:24 -0700
Subject: [PATCH] [loader] add some help text to the error for values without a
 corresponding capture

---
 src/log_format.cc                             | 20 ++++++++++++++++++-
 ...1d6f35e8a9ae4fd3e91ffaa82a037b5a847ab7.err |  3 +++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/log_format.cc b/src/log_format.cc
index b9932de5..72d08542 100644
--- a/src/log_format.cc
+++ b/src/log_format.cc
@@ -1904,6 +1904,8 @@ external_log_format::build(std::vector<lnav::console::user_message>& errors)
         }
 
         if (this->elf_type == elf_type_t::ELF_TYPE_TEXT) {
+            std::set<std::string> available_captures;
+
             bool found_in_pattern = false;
             for (const auto& pat : this->elf_patterns) {
                 auto cap_index = pat.second->p_pcre->name_index(
@@ -1912,8 +1914,20 @@ external_log_format::build(std::vector<lnav::console::user_message>& errors)
                     found_in_pattern = true;
                     break;
                 }
+
+                for (auto name_iter = pat.second->p_pcre->named_begin();
+                     name_iter != pat.second->p_pcre->named_end();
+                     ++name_iter)
+                {
+                    available_captures.insert(name_iter->pnc_name);
+                }
             }
             if (!found_in_pattern) {
+                auto notes
+                    = attr_line_t("the following captures are available:\n  ")
+                          .join(available_captures,
+                                VC_ROLE.value(role_t::VCR_SYMBOL),
+                                ", ");
                 errors.emplace_back(
                     lnav::console::user_message::error(
                         attr_line_t("invalid value ")
@@ -1924,7 +1938,11 @@ external_log_format::build(std::vector<lnav::console::user_message>& errors)
                         .with_reason(
                             attr_line_t("no patterns have a capture named ")
                                 .append_quoted(vd->vd_meta.lvm_name.get()))
-                        .with_snippets(this->get_snippets()));
+                        .with_note(notes)
+                        .with_snippets(this->get_snippets())
+                        .with_help("values are populated from captures in "
+                                   "patterns, so at least one pattern must "
+                                   "have a capture with this value name"));
             }
         }
 
diff --git a/test/expected/test_format_loader.sh_3f1d6f35e8a9ae4fd3e91ffaa82a037b5a847ab7.err b/test/expected/test_format_loader.sh_3f1d6f35e8a9ae4fd3e91ffaa82a037b5a847ab7.err
index 69a66d99..5394f53c 100644
--- a/test/expected/test_format_loader.sh_3f1d6f35e8a9ae4fd3e91ffaa82a037b5a847ab7.err
+++ b/test/expected/test_format_loader.sh_3f1d6f35e8a9ae4fd3e91ffaa82a037b5a847ab7.err
@@ -101,6 +101,9 @@
 ✘ error: invalid value “/invalid_props_log/value/non-existent”
  reason: no patterns have a capture named “non-existent”
  --> {test_dir}/bad-config/formats/invalid-properties/format.json:4
+ = note: the following captures are available:
+           body, pid, timestamp
+ = help: values are populated from captures in patterns, so at least one pattern must have a capture with this value name
 ✘ error: invalid value for property “/invalid_props_log/timestamp-field”
  reason: “ts” was not found in the pattern at /invalid_props_log/regex/std
  --> {test_dir}/bad-config/formats/invalid-properties/format.json:4