libutil-test-support: Add HasSubstrIgnoreANSIMatcher

This matcher is useful for checking error messages, which
always contain ANSI escapes.

src/libutil-test-support/include/nix/util/tests/gmock-matchers.hh

@@ -0,0 +1,56 @@
+#pragma once
+///@file
+
+#include "nix/util/terminal.hh"
+#include <gmock/gmock.h>
+
+namespace nix::testing {
+
+namespace internal {
+
+/**
+ * GMock matcher that matches substring while stripping off all ANSI escapes.
+ * Useful for checking exceptions messages in unit tests.
+ */
+class HasSubstrIgnoreANSIMatcher
+{
+public:
+    explicit HasSubstrIgnoreANSIMatcher(std::string substring)
+        : substring(std::move(substring))
+    {
+    }
+
+    bool MatchAndExplain(const char * s, ::testing::MatchResultListener * listener) const
+    {
+        return s != nullptr && MatchAndExplain(std::string(s), listener);
+    }
+
+    template<typename MatcheeStringType>
+    bool MatchAndExplain(const MatcheeStringType & s, [[maybe_unused]] ::testing::MatchResultListener * listener) const
+    {
+        return filterANSIEscapes(s, /*filterAll=*/true).find(substring) != substring.npos;
+    }
+
+    void DescribeTo(::std::ostream * os) const
+    {
+        *os << "has substring " << substring;
+    }
+
+    void DescribeNegationTo(::std::ostream * os) const
+    {
+        *os << "has no substring " << substring;
+    }
+
+private:
+    std::string substring;
+};
+
+} // namespace internal
+
+inline ::testing::PolymorphicMatcher<internal::HasSubstrIgnoreANSIMatcher>
+HasSubstrIgnoreANSIMatcher(const std::string & substring)
+{
+    return ::testing::MakePolymorphicMatcher(internal::HasSubstrIgnoreANSIMatcher(substring));
+}
+
+} // namespace nix::testing

src/libutil-test-support/include/nix/util/tests/meson.build

@@ -4,6 +4,7 @@ include_dirs = [include_directories('../../..')]
 
 headers = files(
   'characterization.hh',
+  'gmock-matchers.hh',
   'gtest-with-params.hh',
   'hash.hh',
   'nix_api_util.hh',