Add hs_expression_ext_info() API function

This is a variant of hs_expression_info() that can also accept extended
parameters.

src/hs_compile.h

@@ -158,7 +158,7 @@ typedef struct hs_platform_info {
 
 /**
  * A type containing information related to an expression that is returned by
- * @ref hs_expression_info().
+ * @ref hs_expression_info() or @ref hs_expression_ext_info.
  */
 typedef struct hs_expr_info {
     /**
@@ -201,7 +201,8 @@ typedef struct hs_expr_info {
 
 /**
  * A structure containing additional parameters related to an expression,
- * passed in at build time to @ref hs_compile_ext_multi().
+ * passed in at build time to @ref hs_compile_ext_multi() or @ref
+ * hs_expression_ext_info.
  *
  * These parameters allow the set of matches produced by a pattern to be
  * constrained at compile time, rather than relying on the application to
@@ -401,7 +402,7 @@ hs_error_t hs_compile_multi(const char *const *expressions,
                             hs_database_t **db, hs_compile_error_t **error);
 
 /**
- * The multiple regular expression compiler with extended pattern support.
+ * The multiple regular expression compiler with extended parameter support.
  *
  * This function call compiles a group of expressions into a database in the
  * same way as @ref hs_compile_multi(), but allows additional parameters to be
@@ -550,6 +551,62 @@ hs_error_t hs_expression_info(const char *expression, unsigned int flags,
                               hs_expr_info_t **info,
                               hs_compile_error_t **error);
 
+/**
+ * Utility function providing information about a regular expression, with
+ * extended parameter support. The information provided in @ref hs_expr_info_t
+ * includes the minimum and maximum width of a pattern match.
+ *
+ * @param expression
+ *      The NULL-terminated expression to parse. Note that this string must
+ *      represent ONLY the pattern to be matched, with no delimiters or flags;
+ *      any global flags should be specified with the @a flags argument.  For
+ *      example, the expression `/abc?def/i` should be compiled by providing
+ *      `abc?def` as the @a expression, and @ref HS_FLAG_CASELESS as the @a
+ *      flags.
+ *
+ * @param flags
+ *      Flags which modify the behaviour of the expression. Multiple flags may
+ *      be used by ORing them together. Valid values are:
+ *       - HS_FLAG_CASELESS - Matching will be performed case-insensitively.
+ *       - HS_FLAG_DOTALL - Matching a `.` will not exclude newlines.
+ *       - HS_FLAG_MULTILINE - `^` and `$` anchors match any newlines in data.
+ *       - HS_FLAG_SINGLEMATCH - Only one match will be generated by the
+ *                               expression per stream.
+ *       - HS_FLAG_ALLOWEMPTY - Allow expressions which can match against an
+ *                              empty string, such as `.*`.
+ *       - HS_FLAG_UTF8 - Treat this pattern as a sequence of UTF-8 characters.
+ *       - HS_FLAG_UCP - Use Unicode properties for character classes.
+ *       - HS_FLAG_PREFILTER - Compile pattern in prefiltering mode.
+ *       - HS_FLAG_SOM_LEFTMOST - Report the leftmost start of match offset
+ *                                when a match is found.
+ *
+ * @param ext
+ *      A pointer to a filled @ref hs_expr_ext_t structure that defines
+ *      extended behaviour for this pattern. NULL may be specified if no
+ *      extended parameters are needed.
+ *
+ * @param info
+ *      On success, a pointer to the pattern information will be returned in
+ *      this parameter, or NULL on failure. This structure is allocated using
+ *      the allocator supplied in @ref hs_set_allocator() (or malloc() if no
+ *      allocator was set) and should be freed by the caller.
+ *
+ * @param error
+ *      If the call fails, a pointer to a @ref hs_compile_error_t will be
+ *      returned, providing details of the error condition. The caller is
+ *      responsible for deallocating the buffer using the @ref
+ *      hs_free_compile_error() function.
+ *
+ * @return
+ *      @ref HS_SUCCESS is returned on successful compilation; @ref
+ *      HS_COMPILER_ERROR on failure, with details provided in the error
+ *      parameter.
+ */
+hs_error_t hs_expression_ext_info(const char *expression, unsigned int flags,
+                                  const hs_expr_ext_t *ext,
+                                  hs_expr_info_t **info,
+                                  hs_compile_error_t **error);
+
 /**
  * Populates the platform information based on the current host.
  *