Merge pull request #1887 from contour-terminal/fix/1861

Remove empty-string terminfo capabilities that cause input to be swallowed

Author: christianparpart

metainfo.xml

@@ -107,6 +107,7 @@
     <release version="0.6.3" urgency="medium" type="development">
       <description>
         <ul>
+          <li>Fixes keyboard input being swallowed in programs like less and bat due to empty-string terminfo capabilities (#1861)</li>
           <li>Fixes F3 key not reaching PTY applications when a keybinding matches but its action does not execute, by falling through to the terminal instead of silently consuming the key event</li>
           <li>Fixes F3/Shift+F3 search navigation keybindings firing in any mode instead of only when Search mode is active</li>
           <li>Fixes build failure on Alpine Linux (musl libc) due to missing close_range() function (#1879)</li>

src/vtbackend/Capabilities.cpp

@@ -274,10 +274,6 @@ namespace
         String { Undefined, "kUP5"sv, "\033[1;5A"sv },
         String { Undefined, "kUP6"sv, "\033[1;6A"sv },
         String { Undefined, "kUP7"sv, "\033[1;7A"sv },
-        String { "K1"_tcap, "ka1"sv, ""sv },         // upper left of keypad
-        String { "K3"_tcap, "ka3"sv, ""sv },         // upper right of keypad
-        String { "K4"_tcap, "kc1"sv, ""sv },         // center of keypad
-        String { "K5"_tcap, "kc3"sv, ""sv },         // lower right of keypad
         String { "kl"_tcap, "kcub1"sv, "\033OD"sv }, // app: cursor left
         String { "kd"_tcap, "kcud1"sv, "\033OB"sv }, // app: cursor left
         String { "kr"_tcap, "kcuf1"sv, "\033OC"sv }, // app: cursor right
@@ -347,14 +343,11 @@ namespace
         String { "k7"_tcap, "kf7"sv, "\033[18~"sv },
         String { "k8"_tcap, "kf8"sv, "\033[19~"sv },
         String { "k9"_tcap, "kf9"sv, "\033[20~"sv },
-        String { "%1"_tcap, "khlp"sv, ""sv },
         String { "kh"_tcap, "khome"sv, "\033OH"sv },
         String { "kI"_tcap, "kich1"sv, "\033[2~"sv },
         String { "Km"_tcap, "kmous"sv, "\033[M"sv },
         String { "kN"_tcap, "knp"sv, "\033[6~"sv },
         String { "kP"_tcap, "kpp"sv, "\033[5~"sv },
-        String { "&8"_tcap, "kund"sv, ""sv },
-
         // {{{ Extensions originally introduced by tmux.
         //
         String { "Ss"_tcap, "Ss"sv, "\033[%p1%d q" }, // Set cursor style.
@@ -492,7 +485,7 @@ string StaticDatabase::terminfo() const
             output << "    " << cap.name << "#" << cap.value << ",\n";
 
     for (auto const& cap: strings)
-        if (!cap.name.empty())
+        if (!cap.name.empty() && !cap.value.empty())
             output << "    " << cap.name << "=" << crispy::escape(cap.value, crispy::numeric_escape::Octal)
                    << ",\n";
 

src/vtbackend/Capabilities_test.cpp

@@ -5,7 +5,8 @@
 
 #include <catch2/catch_test_macros.hpp>
 
-#include <format>
+#include <regex>
+#include <string>
 
 using namespace std::string_view_literals;
 using crispy::fromHexString;
@@ -32,3 +33,85 @@ TEST_CASE("Capabilities.get")
     auto const bce = tcap.numericCapability("bce");
     REQUIRE(bce);
 }
+
+// Issue #1861: Empty string terminfo capabilities cause input to be swallowed in programs
+// like less and bat. When capabilities are defined as empty strings (e.g., "ka1=,"),
+// buggy parsers match any input against them.
+TEST_CASE("Capabilities.terminfo_no_empty_string_values", "[issue-1861]")
+{
+    vtbackend::capabilities::StaticDatabase const tcap;
+    auto const terminfo = tcap.terminfo();
+
+    // The regex matches sequences like "\n    name=,\n" where the value after '=' is empty.
+    // In terminfo format, "name=value," defines a string capability.
+    // "name=,\n" means the value is an empty string — this must never appear.
+    // Note: We avoid std::regex::multiline because MSVC does not support it.
+    auto const emptyValuePattern = std::regex(R"(\n\s+(\w+)=,\n)");
+
+    auto begin = std::sregex_iterator(terminfo.begin(), terminfo.end(), emptyValuePattern);
+    auto end = std::sregex_iterator();
+
+    std::string emptyCapNames;
+    for (auto it = begin; it != end; ++it)
+    {
+        if (!emptyCapNames.empty())
+            emptyCapNames += ", ";
+        emptyCapNames += (*it)[1].str();
+    }
+
+    INFO("Capabilities with empty string values: " << emptyCapNames);
+    CHECK(emptyCapNames.empty());
+}
+
+// Verify that previously-empty keypad capabilities (ka1, ka3, kc1, kc3) are no longer
+// present in the terminfo output at all — they should be omitted, not set to empty.
+TEST_CASE("Capabilities.keypad_caps_not_in_terminfo", "[issue-1861]")
+{
+    vtbackend::capabilities::StaticDatabase const tcap;
+    auto const terminfo = tcap.terminfo();
+
+    CHECK(terminfo.find("ka1=") == std::string::npos);
+    CHECK(terminfo.find("ka3=") == std::string::npos);
+    CHECK(terminfo.find("kc1=") == std::string::npos);
+    CHECK(terminfo.find("kc3=") == std::string::npos);
+}
+
+// Verify that khlp and kund (which were also empty) are omitted.
+TEST_CASE("Capabilities.help_undo_caps_not_in_terminfo", "[issue-1861]")
+{
+    vtbackend::capabilities::StaticDatabase const tcap;
+    auto const terminfo = tcap.terminfo();
+
+    CHECK(terminfo.find("khlp=") == std::string::npos);
+    CHECK(terminfo.find("kund=") == std::string::npos);
+}
+
+// Verify that non-empty string capabilities are still present in terminfo output.
+TEST_CASE("Capabilities.non_empty_caps_still_present", "[issue-1861]")
+{
+    vtbackend::capabilities::StaticDatabase const tcap;
+    auto const terminfo = tcap.terminfo();
+
+    // These are well-known capabilities that must still be present.
+    CHECK(terminfo.find("bold=") != std::string::npos);
+    CHECK(terminfo.find("clear=") != std::string::npos);
+    CHECK(terminfo.find("kcub1=") != std::string::npos);
+    CHECK(terminfo.find("kcud1=") != std::string::npos);
+    CHECK(terminfo.find("kf1=") != std::string::npos);
+    CHECK(terminfo.find("smkx=") != std::string::npos);
+    CHECK(terminfo.find("rmkx=") != std::string::npos);
+}
+
+// Verify that the stringCapability() API returns an empty view for removed capabilities,
+// confirming they are no longer part of the static database.
+TEST_CASE("Capabilities.removed_caps_return_empty_from_api", "[issue-1861]")
+{
+    vtbackend::capabilities::StaticDatabase const tcap;
+
+    CHECK(tcap.stringCapability("ka1").empty());
+    CHECK(tcap.stringCapability("ka3").empty());
+    CHECK(tcap.stringCapability("kc1").empty());
+    CHECK(tcap.stringCapability("kc3").empty());
+    CHECK(tcap.stringCapability("khlp").empty());
+    CHECK(tcap.stringCapability("kund").empty());
+}