Correct behavior of string match variable import with multiple arguments

This refactors the behavior of string match with capture groups to
correctly handle multiple arguments. Now the variable capture applies to
the first match, as documented. Fixes #7938.

CHANGELOG.rst

@@ -20,7 +20,7 @@ Scripting improvements
 - ``echo`` no longer writes its output one byte at a time, improving performance and allowing use with linux' special API files (``/proc``, ``/sys`` and such) (:issue:`7836`).
 - fish should now better handle ``cd`` on filesystems with broken ``stat(3)`` responses (:issue:`7577`).
 - Builtins now properly report a ``$status`` of 1 upon unsuccessful writes (:issue:`7857`).
-- ``string match`` with unmatched capture groups and without the ``--all`` flag now sets an empty variable instead of a variable containing the empty string, matching the documentation.
+- ``string match`` with unmatched capture groups and without the ``--all`` flag now sets an empty variable instead of a variable containing the empty string. It also correctly imports the first match if multiple arguments are provided, matching the documentation. (:issue:`7938`).
 - Better errors when a command in a command substitution wasn't found or is not allowed.
 
 Interactive improvements

src/builtin_string.cpp

@@ -737,6 +737,7 @@ class string_matcher_t {
     int match_count() const { return total_matched; }
 
     virtual bool is_valid() const = 0;
+    virtual void clear_capture_vars() {}
 };
 
 class wildcard_matcher_t final : public string_matcher_t {
@@ -802,6 +803,9 @@ struct compiled_regex_t {
     pcre2_code *code{nullptr};
     pcre2_match_data *match{nullptr};
 
+    // The list of named capture groups.
+    wcstring_list_t capture_group_names;
+
     compiled_regex_t(const wchar_t *argv0, const wcstring &pattern, bool ignore_case,
                      io_streams_t &streams) {
         // Disable some sequences that can lead to security problems.
@@ -824,8 +828,74 @@ struct compiled_regex_t {
             return;
         }
 
+        this->capture_group_names = get_capture_group_names(code);
+        if (!validate_capture_group_names(streams)) {
+            return;
+        }
+
         match = pcre2_match_data_create_from_pattern(code, nullptr);
         assert(match);
+        this->valid_ = true;
+    }
+
+    /// \return the list of capture group names from \p code.
+    static wcstring_list_t get_capture_group_names(const pcre2_code *code) {
+        PCRE2_SPTR name_table;
+        uint32_t name_entry_size;
+        uint32_t name_count;
+
+        pcre2_pattern_info(code, PCRE2_INFO_NAMETABLE, &name_table);
+        pcre2_pattern_info(code, PCRE2_INFO_NAMEENTRYSIZE, &name_entry_size);
+        pcre2_pattern_info(code, PCRE2_INFO_NAMECOUNT, &name_count);
+
+        struct name_table_entry_t {
+#if PCRE2_CODE_UNIT_WIDTH == 8
+            uint8_t match_index_msb;
+            uint8_t match_index_lsb;
+#if CHAR_BIT == PCRE2_CODE_UNIT_WIDTH
+            char name[];
+#else
+            char8_t name[];
+#endif
+#elif PCRE2_CODE_UNIT_WIDTH == 16
+            uint16_t match_index;
+#if WCHAR_T_BITS == PCRE2_CODE_UNIT_WIDTH
+            wchar_t name[];
+#else
+            char16_t name[];
+#endif
+#else
+            uint32_t match_index;
+#if WCHAR_T_BITS == PCRE2_CODE_UNIT_WIDTH
+            wchar_t name[];
+#else
+            char32_t name[];
+#endif  // WCHAR_T_BITS
+#endif  // PCRE2_CODE_UNIT_WIDTH
+        };
+
+        const auto *names = reinterpret_cast<const name_table_entry_t *>(name_table);
+        wcstring_list_t result;
+        result.reserve(name_count);
+        for (uint32_t i = 0; i < name_count; ++i) {
+            const auto &name_entry = names[i * name_entry_size];
+            result.emplace_back(name_entry.name);
+        }
+        return result;
+    }
+
+    /// Check if our capture group names are valid. If any are invalid then report an error to \p
+    /// streams. \return true if all names are valid.
+    bool validate_capture_group_names(io_streams_t &streams) {
+        for (const wcstring &name : this->capture_group_names) {
+            if (env_var_t::flags_for(name.c_str()) & env_var_t::flag_read_only) {
+                // Modification of read-only variables is not allowed
+                streams.err.append_format(
+                    L"Modification of read-only variable \"%ls\" is not allowed\n", name.c_str());
+                return false;
+            }
+        }
+        return true;
     }
 
     ~compiled_regex_t() {
@@ -833,10 +903,13 @@ struct compiled_regex_t {
         pcre2_code_free(code);
     }
 
-    bool is_valid() const { return this->code != nullptr; }
+    bool is_valid() const { return this->valid_; }
 
     compiled_regex_t(const compiled_regex_t &) = delete;
     void operator=(const compiled_regex_t &) = delete;
+
+   private:
+    bool valid_{false};
 };
 
 class pcre2_matcher_t final : public string_matcher_t {
@@ -901,76 +974,25 @@ class pcre2_matcher_t final : public string_matcher_t {
 
     class regex_importer_t {
        private:
-        std::map<wcstring, std::vector<wcstring>> matches_;
-        parser_t &parser_;
+        std::map<wcstring, wcstring_list_t> matches_;
+        env_stack_t &vars_;
         const wcstring &haystack_;
         const compiled_regex_t &regex_;
         const bool all_flag_;
-        bool regex_valid_ = false;
+        bool do_import_{false};
 
        public:
-        regex_importer_t(parser_t &parser, const wcstring &haystack, const compiled_regex_t &regex,
+        regex_importer_t(env_stack_t &vars, const wcstring &haystack, const compiled_regex_t &regex,
                          bool all_flag)
-            : parser_(parser), haystack_(haystack), regex_(regex), all_flag_(all_flag) {}
-
-        /// Enumerates the named groups in the compiled PCRE2 expression, validates the names of
-        /// the groups as variable names, and initializes their value (overriding any previous
-        /// contents).
-        bool init(io_streams_t &streams) {
-            PCRE2_SPTR name_table;
-            uint32_t name_entry_size;
-            uint32_t name_count;
-
-            pcre2_pattern_info(regex_.code, PCRE2_INFO_NAMETABLE, &name_table);
-            pcre2_pattern_info(regex_.code, PCRE2_INFO_NAMEENTRYSIZE, &name_entry_size);
-            pcre2_pattern_info(regex_.code, PCRE2_INFO_NAMECOUNT, &name_count);
-
-            struct name_table_entry_t {
-#if PCRE2_CODE_UNIT_WIDTH == 8
-                uint8_t match_index_msb;
-                uint8_t match_index_lsb;
-#if CHAR_BIT == PCRE2_CODE_UNIT_WIDTH
-                char name[];
-#else
-                char8_t name[];
-#endif
-#elif PCRE2_CODE_UNIT_WIDTH == 16
-                uint16_t match_index;
-#if WCHAR_T_BITS == PCRE2_CODE_UNIT_WIDTH
-                wchar_t name[];
-#else
-                char16_t name[];
-#endif
-#else
-                uint32_t match_index;
-#if WCHAR_T_BITS == PCRE2_CODE_UNIT_WIDTH
-                wchar_t name[];
-#else
-                char32_t name[];
-#endif  // WCHAR_T_BITS
-#endif  // PCRE2_CODE_UNIT_WIDTH
-            };
-
-            auto *names = static_cast<name_table_entry_t *>((void *)(name_table));
-            for (uint32_t i = 0; i < name_count; ++i) {
-                const auto &name_entry = names[i * name_entry_size];
-
-                if (env_var_t::flags_for(name_entry.name) & env_var_t::flag_read_only) {
-                    // Modification of read-only variables is not allowed
-                    streams.err.append_format(
-                        L"Modification of read-only variable \"%S\" is not allowed\n",
-                        name_entry.name);
-                    return false;
-                }
-                matches_.emplace(name_entry.name, std::vector<wcstring>{});
+            : vars_(vars), haystack_(haystack), regex_(regex), all_flag_(all_flag) {
+            for (const wcstring &name : regex_.capture_group_names) {
+                matches_.emplace(name, wcstring_list_t{});
             }
-
-            regex_valid_ = true;
-            return true;
         }
 
         /// This member function should be called each time a match is found
         void import_vars() {
+            do_import_ = true;
             PCRE2_SIZE *ovector = pcre2_get_ovector_pointer(regex_.match);
             for (auto &kv : matches_) {
                 const auto &name = kv.first;
@@ -1014,15 +1036,11 @@ class pcre2_matcher_t final : public string_matcher_t {
         }
 
         ~regex_importer_t() {
-            if (!regex_valid_) {
-                return;
-            }
-
-            auto &vars = parser_.vars();
+            if (!do_import_) return;
             for (auto &kv : matches_) {
                 const wcstring &name = kv.first;
                 wcstring_list_t &value = kv.second;
-                vars.set(name, ENV_DEFAULT, std::move(value));
+                vars_.set(name, ENV_DEFAULT, std::move(value));
             }
         }
     };
@@ -1042,24 +1060,18 @@ class pcre2_matcher_t final : public string_matcher_t {
         // an unrecoverable error.
         assert(regex.code && "report_matches should only be called if the regex was valid");
 
-        regex_importer_t var_importer(this->parser, arg, this->regex, opts.all);
+        regex_importer_t var_importer(this->parser.vars(), arg, this->regex, opts.all);
 
-        // We must manually init the importer rather than relegating this to the constructor
-        // because it will validate the names it is importing to make sure they're all legal and
-        // writeable.
-        if (!var_importer.init(streams)) {
-            // init() directly reports errors itself so it can specify the problem variable
-            return false;
-        }
         // See pcre2demo.c for an explanation of this logic.
         PCRE2_SIZE arglen = arg.length();
         auto rc = report_match(arg, pcre2_match(regex.code, PCRE2_SPTR(arg.c_str()), arglen, 0, 0,
                                                 regex.match, nullptr));
+
         // We only import variables for the *first matching argument*
-        bool had_match = false;
-        if (rc == match_result_t::match && !imported_vars) {
+        bool do_var_import = (rc == match_result_t::match && !imported_vars);
+        if (do_var_import) {
             var_importer.import_vars();
-            had_match = true;
+            imported_vars = true;
         }
 
         switch (rc) {
@@ -1074,7 +1086,7 @@ class pcre2_matcher_t final : public string_matcher_t {
         if (opts.invert_match) return true;
 
         // Report any additional matches.
-        for (auto ovector = pcre2_get_ovector_pointer(regex.match); opts.all; total_matched++) {
+        for (auto *ovector = pcre2_get_ovector_pointer(regex.match); opts.all; total_matched++) {
             uint32_t options = 0;
             PCRE2_SIZE offset = ovector[1];  // start at end of previous match
 
@@ -1092,7 +1104,7 @@ class pcre2_matcher_t final : public string_matcher_t {
             }
 
             // Call import_vars() before modifying the ovector
-            if (rc == match_result_t::match) {
+            if (rc == match_result_t::match && do_var_import) {
                 var_importer.import_vars();
             }
 
@@ -1101,11 +1113,17 @@ class pcre2_matcher_t final : public string_matcher_t {
                 ovector[1] = offset + 1;
             }
         }
-
-        imported_vars |= had_match;
         return true;
     }
 
+    /// Override to clear our capture variables if we had no match.
+    void clear_capture_vars() override {
+        assert(!imported_vars && "Should not already have imported variables");
+        for (const wcstring &name : regex.capture_group_names) {
+            parser.vars().set_empty(name, ENV_DEFAULT);
+        }
+    }
+
     bool is_valid() const override { return regex.is_valid(); }
 };
 
@@ -1150,6 +1168,10 @@ static int string_match(parser_t &parser, io_streams_t &streams, int argc, const
         if (opts.quiet && matcher->match_count() > 0) return STATUS_CMD_OK;
     }
 
+    if (matcher->match_count() == 0) {
+        matcher->clear_capture_vars();
+    }
+
     return matcher->match_count() > 0 ? STATUS_CMD_OK : STATUS_CMD_ERROR;
 }
 

tests/checks/regex-import.fish

@@ -97,3 +97,26 @@ set --show text
 # CHECK: $text[2]: |aaa|
 # CHECK: $text[3]: ||
 # CHECK: $text[4]: |bbb|
+
+# Regression test for #7938.
+set -e text
+echo one\ntwo | string match -ra '(?<text>[a-z]+)'
+# CHECK: one
+# CHECK: one
+# CHECK: two
+# CHECK: two
+set --show text
+# CHECK: $text: set in global scope, unexported, with 1 elements
+# CHECK: $text[1]: |one|
+
+set -e text
+echo three\nfour | string match -qra '(?<text>[a-z]+)'
+set --show text
+# CHECK: $text: set in global scope, unexported, with 1 elements
+# CHECK: $text[1]: |three|
+
+set -e text
+echo 555\nsix | string match -qra '(?<text>[a-z]+)'
+set --show text
+# CHECK: $text: set in global scope, unexported, with 1 elements
+# CHECK: $text[1]: |six|