From 584a50d0dc3bf450c91c6cab560656f65b01eeb1 Mon Sep 17 00:00:00 2001
From: Jon Ross-Perkins <jperkins@google.com>
Date: Wed, 15 Mar 2023 18:01:48 -0700
Subject: [PATCH] Fix check-diagnostics for pre-commit (#2683)

Unused diagnostics were incorrectly always returning "false" regardless of whether there was an issue. It was still looking for registry file changes, not kind file changes. Also, this should only be run once per pre-commit run (pass_filenames=false).

Remove the one unused diagnostic.
---
 .pre-commit-config.yaml                    | 4 +++-
 toolchain/diagnostics/check_diagnostics.py | 6 ++++--
 toolchain/diagnostics/diagnostic_kind.def  | 3 ---
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 5b98f6072992..133a2b11e5ed 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -103,8 +103,10 @@ repos:
           (?x)^(
               toolchain/.*\.cpp|
               toolchain/.*\.h|
-              toolchain/diagnostics/diagnostic_registry\.def
+              toolchain/diagnostics/check_diagnostics\.py|
+              toolchain/diagnostics/diagnostic_kind\.def
           )$
+        pass_filenames: false
 
   # Run linters last, as formatters and other checks may fix issues.
   - repo: local
diff --git a/toolchain/diagnostics/check_diagnostics.py b/toolchain/diagnostics/check_diagnostics.py
index b2154a71defb..4c4db33237dc 100755
--- a/toolchain/diagnostics/check_diagnostics.py
+++ b/toolchain/diagnostics/check_diagnostics.py
@@ -15,8 +15,8 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 import collections
 from concurrent import futures
 import itertools
-from pathlib import Path
 import os
+from pathlib import Path
 import re
 import sys
 from typing import Dict, List, NamedTuple, Set
@@ -98,9 +98,11 @@ def check_uniqueness(uses: Dict[str, List[Location]]) -> bool:
 def check_unused(decls: Set[str], uses: Dict[str, List[Location]]) -> bool:
     """If any diagnostic is unused, prints an error and returns true."""
     unused = decls.difference(uses.keys())
+    if not unused:
+        return False
     for diag in sorted(unused):
         print(f"Unused diagnostic: {diag}")
-    return False
+    return True
 
 
 def main() -> None:
diff --git a/toolchain/diagnostics/diagnostic_kind.def b/toolchain/diagnostics/diagnostic_kind.def
index 9dfda228fa1c..ff4bfefa223f 100644
--- a/toolchain/diagnostics/diagnostic_kind.def
+++ b/toolchain/diagnostics/diagnostic_kind.def
@@ -84,9 +84,6 @@ CARBON_DIAGNOSTIC_KIND(ExpectedDeclarationName)
 CARBON_DIAGNOSTIC_KIND(ExpectedDeclarationSemiOrDefinition)
 CARBON_DIAGNOSTIC_KIND(MethodImplNotAllowed)
 
-// Class and interface diagnostics
-CARBON_DIAGNOSTIC_KIND(ExpectedDeducedParam)
-
 // ============================================================================
 // Semantics diagnostics
 // ============================================================================