feat(kernel/error_msgs): improve cryptic type mismatch error messages where the types may seem identical because key information is being suppressed

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/frontends/lean/parser.cpp

@@ -17,6 +17,7 @@ Author: Leonardo de Moura
 #include "kernel/replace_fn.h"
 #include "kernel/abstract.h"
 #include "kernel/instantiate.h"
+#include "kernel/error_msgs.h"
 #include "library/parser_nested_exception.h"
 #include "library/aliases.h"
 #include "library/private.h"
@@ -34,6 +35,7 @@ Author: Leonardo de Moura
 #include "frontends/lean/parser_bindings.h"
 #include "frontends/lean/notation_cmd.h"
 #include "frontends/lean/elaborator.h"
+#include "frontends/lean/pp_options.h"
 
 #ifndef LEAN_DEFAULT_PARSER_SHOW_ERRORS
 #define LEAN_DEFAULT_PARSER_SHOW_ERRORS true
@@ -1043,6 +1045,7 @@ void parser::parse_imports() {
 bool parser::parse_commands() {
     // We disable hash-consing while parsing to make sure the pos-info are correct.
     scoped_expr_caching disable(false);
+    scoped_set_distinguishing_pp_options set(get_distinguishing_pp_options());
     try {
         bool done = false;
         parse_imports();

src/frontends/lean/pp.cpp

@@ -99,7 +99,8 @@ expr pretty_fn::purify(expr const & e) {
         });
 }
 
-void pretty_fn::set_options(options const & o) {
+void pretty_fn::set_options_core(options const & o) {
+    m_options       = o;
     m_indent        = get_pp_indent(o);
     m_max_depth     = get_pp_max_depth(o);
     m_max_steps     = get_pp_max_steps(o);
@@ -112,6 +113,12 @@ void pretty_fn::set_options(options const & o) {
     m_private_names = get_pp_private_names(o);
 }
 
+void pretty_fn::set_options(options const & o) {
+    if (is_eqp(o, m_options))
+        return;
+    set_options_core(o);
+}
+
 format pretty_fn::pp_level(level const & l) {
     return ::lean::pp(l, m_unicode, m_indent);
 }
@@ -411,7 +418,7 @@ auto pretty_fn::pp(expr const & e) -> result {
 
 pretty_fn::pretty_fn(environment const & env, options const & o):
     m_env(env), m_tc(env) {
-    set_options(o);
+    set_options_core(o);
     m_meta_prefix   = "M";
     m_next_meta_idx = 1;
 }
@@ -424,7 +431,8 @@ format pretty_fn::operator()(expr const & e) {
 formatter_factory mk_pretty_formatter_factory() {
     return [](environment const & env, options const & o) { // NOLINT
         auto fn_ptr = std::make_shared<pretty_fn>(env, o);
-        return formatter(o, [=](expr const & e) {
+        return formatter(o, [=](expr const & e, options const & new_o) {
+                fn_ptr->set_options(new_o);
                 return (*fn_ptr)(e);
             });
     };

src/frontends/lean/pp.h

@@ -29,6 +29,7 @@ private:
     name_map<name>     m_purify_local_table;
     name_set           m_purify_used_locals;
     // cached configuration
+    options            m_options;
     unsigned           m_indent;
     unsigned           m_max_depth;
     unsigned           m_max_steps;
@@ -40,8 +41,6 @@ private:
     bool               m_full_names;
     bool               m_private_names;
 
-    void set_options(options const & o);
-
     unsigned max_bp() const { return std::numeric_limits<unsigned>::max(); }
     name mk_metavar_name(name const & m);
     name mk_local_name(name const & n, name const & suggested);
@@ -69,11 +68,13 @@ private:
     result pp_have(expr const & e);
     result pp_show(expr const & e);
     result pp_macro(expr const & e);
+    void set_options_core(options const & o);
 
 public:
     pretty_fn(environment const & env, options const & o);
     result pp(expr const & e);
-
+    void set_options(options const & o);
+    options const & get_options() const { return m_options; }
     format operator()(expr const & e);
 };
 

src/frontends/lean/pp_options.cpp

@@ -48,6 +48,18 @@ static name g_pp_universes        {"pp", "universes"};
 static name g_pp_full_names       {"pp", "full_names"};
 static name g_pp_private_names    {"pp", "private_names"};
 
+list<options> const & get_distinguishing_pp_options() {
+    static options g_universes_true(g_pp_universes, true);
+    static options g_implicit_true(g_pp_implicit, true);
+    static options g_coercion_true(g_pp_coercion, true);
+    static options g_notation_false(g_pp_notation, false);
+    static options g_implicit_coercion = join(g_coercion_true, g_implicit_true);
+    static options g_implicit_notation = join(g_notation_false, g_implicit_true);
+    static options g_all = join(join(g_universes_true, g_implicit_true), join(g_coercion_true, g_notation_false));
+    static list<options> g_distinguishing_pp_options({g_universes_true, g_implicit_true, g_coercion_true, g_implicit_coercion, g_implicit_notation, g_all});
+    return g_distinguishing_pp_options;
+}
+
 RegisterUnsignedOption(g_pp_max_depth, LEAN_DEFAULT_PP_MAX_DEPTH,
                        "(pretty printer) maximum expression depth, after that it will use ellipsis");
 RegisterUnsignedOption(g_pp_max_steps, LEAN_DEFAULT_PP_MAX_STEPS,

src/frontends/lean/pp_options.h

@@ -15,4 +15,5 @@ bool     get_pp_coercion(options const & opts);
 bool     get_pp_universes(options const & opts);
 bool     get_pp_full_names(options const & opts);
 bool     get_pp_private_names(options const & opts);
+list<options> const & get_distinguishing_pp_options();
 }

src/kernel/error_msgs.cpp

@@ -4,6 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 
 Author: Leonardo de Moura
 */
+#include <string>
 #include "kernel/error_msgs.h"
 
 namespace lean {
@@ -19,35 +20,88 @@ format pp_function_expected(formatter const & fmt, expr const & e) {
     return compose(format("function expected at"), pp_indent_expr(fmt, e));
 }
 
+MK_THREAD_LOCAL_GET_DEF(list<options>, get_distinguishing_pp_options)
+
+list<options> set_distinguishing_pp_options(list<options> const & opts) {
+    list<options> r = get_distinguishing_pp_options();
+    get_distinguishing_pp_options() = opts;
+    return r;
+}
+
+static std::tuple<format, format> pp_until_different(formatter const & fmt, expr const & e1, expr const & e2, list<options> extra) {
+    formatter fmt1 = fmt;
+    while (true) {
+        format r1 = pp_indent_expr(fmt1, e1);
+        format r2 = pp_indent_expr(fmt1, e2);
+        if (!format_pp_eq(r1, r2, fmt1.get_options()))
+            return mk_pair(r1, r2);
+        if (!extra)
+            return mk_pair(pp_indent_expr(fmt, e1), pp_indent_expr(fmt, e2));
+        options o = join(head(extra), fmt.get_options());
+        fmt1  = fmt.update_options(o);
+        extra = tail(extra);
+    }
+}
+
+std::tuple<format, format> pp_until_different(formatter const & fmt, expr const & e1, expr const & e2) {
+    return pp_until_different(fmt, e1, e2, get_distinguishing_pp_options());
+}
+
 format pp_app_type_mismatch(formatter const & fmt, expr const & app, expr const & expected_type, expr const & given_type) {
     format r;
+    format expected_fmt, given_fmt;
+    std::tie(expected_fmt, given_fmt) = pp_until_different(fmt, expected_type, given_type);
     r += format("type mismatch at application");
     r += pp_indent_expr(fmt, app);
     r += compose(line(), format("expected type:"));
-    r += pp_indent_expr(fmt, expected_type);
+    r += expected_fmt;
     r += compose(line(), format("given type:"));
-    r += pp_indent_expr(fmt, given_type);
+    r += given_fmt;
     return r;
 }
 
 format pp_def_type_mismatch(formatter const & fmt, name const & n, expr const & expected_type, expr const & given_type) {
+    format expected_fmt, given_fmt;
+    std::tie(expected_fmt, given_fmt) = pp_until_different(fmt, expected_type, given_type);
     format r("type mismatch at definition '");
     r += format(n);
     r += format("', expected type");
-    r += pp_indent_expr(fmt, expected_type);
+    r += expected_fmt;
     r += compose(line(), format("given type:"));
-    r += pp_indent_expr(fmt, given_type);
+    r += given_fmt;
     return r;
 }
 
 format pp_type_mismatch(formatter const & fmt, expr const & expected_type, expr const & given_type) {
+    format expected_fmt, given_fmt;
+    std::tie(expected_fmt, given_fmt) = pp_until_different(fmt, expected_type, given_type);
     format r("type mismatch, expected type:");
-    r += ::lean::pp_indent_expr(fmt, expected_type);
+    r += expected_fmt;
     r += compose(line(), format("given type:"));
-    r += ::lean::pp_indent_expr(fmt, given_type);
+    r += given_fmt;
     return r;
 }
 
+static format pp_until_meta_visible(formatter const & fmt, expr const & e, list<options> extra) {
+    formatter fmt1 = fmt;
+    while (true) {
+        format r = pp_indent_expr(fmt1, e);
+        std::ostringstream out;
+        out << mk_pair(r, fmt1.get_options());
+        if (out.str().find("?M") != std::string::npos)
+            return r;
+        if (!extra)
+            return pp_indent_expr(fmt, e);
+        options o = join(head(extra), fmt.get_options());
+        fmt1  = fmt.update_options(o);
+        extra = tail(extra);
+    }
+}
+
+format pp_until_meta_visible(formatter const & fmt, expr const & e) {
+    return pp_until_meta_visible(fmt, e, get_distinguishing_pp_options());
+}
+
 format pp_decl_has_metavars(formatter const & fmt, name const & n, expr const & e, bool is_type) {
     format r("failed to add declaration '");
     r += format(n);
@@ -57,7 +111,7 @@ format pp_decl_has_metavars(formatter const & fmt, name const & n, expr const &
     else
         r += format("value");
     r += format(" has metavariables");
-    r += pp_indent_expr(fmt, e);
+    r += pp_until_meta_visible(fmt, e);
     return r;
 }
 }

src/kernel/error_msgs.h

@@ -15,4 +15,20 @@ format pp_app_type_mismatch(formatter const & fmt, expr const & app, expr const
 format pp_def_type_mismatch(formatter const & fmt, name const & n, expr const & expected_type, expr const & given_type);
 format pp_type_mismatch(formatter const & fmt, expr const & expected_type, expr const & given_type);
 format pp_decl_has_metavars(formatter const & fmt, name const & n, expr const & e, bool is_type);
+
+/** \brief Set a list extra configuration options that are used to try to distinguish error such as given/expected type mismatch
+    This is a trick used to avoid cryptic error messages when to types seem identical because the pretty printer is suppressing
+    universes and/or implicit arguments. The error messages will keep using these extra options until it finds one that
+    can distinguish given/expected type. The extra options do not override user provided options.
+
+    \remark This is a thread local information.
+    \remark Consider using #scoped_set_distinguishing_pp_options
+*/
+list<options> set_distinguishing_pp_options(list<options> const & opts);
+struct scoped_set_distinguishing_pp_options {
+    list<options> m_old;
+    scoped_set_distinguishing_pp_options(list<options> const & os):m_old(set_distinguishing_pp_options(os)) {}
+    ~scoped_set_distinguishing_pp_options() { set_distinguishing_pp_options(m_old); }
+};
+std::tuple<format, format> pp_until_different(formatter const & fmt, expr const & e1, expr const & e2);
 }

src/kernel/formatter.cpp

@@ -246,7 +246,7 @@ std::ostream & operator<<(std::ostream & out, expr const & e) {
 
 formatter_factory mk_simple_formatter_factory() {
     return [](environment const & env, options const & o) { // NOLINT
-        return formatter(o, [=](expr const & e) {
+        return formatter(o, [=](expr const & e, options const &) {
                 std::ostringstream s;
                 print_expr_fn pr(s, env.prop_proof_irrel());
                 pr(e);

src/kernel/formatter.h

@@ -28,12 +28,13 @@ std::pair<expr, expr> binding_body_fresh(expr const & b, bool preserve_type = fa
 std::pair<expr, expr> let_body_fresh(expr const & l, bool preserve_type = false);
 
 class formatter {
-    std::function<format(expr const &)> m_fn;
+    std::function<format(expr const &, options const &)> m_fn;
     options                             m_options;
 public:
-    formatter(options const & o, std::function<format(expr const &)> const & fn):m_fn(fn), m_options(o) {}
-    format operator()(expr const & e) const { return m_fn(e); }
+    formatter(options const & o, std::function<format(expr const &, options const &)> const & fn):m_fn(fn), m_options(o) {}
+    format operator()(expr const & e) const { return m_fn(e, m_options); }
     options const & get_options() const { return m_options; }
+    formatter update_options(options const & o) const { return formatter(o, m_fn); }
 };
 
 typedef std::function<formatter(environment const &, options const &)> formatter_factory;

src/util/sexpr/format.cpp

@@ -350,6 +350,14 @@ std::ostream & operator<<(std::ostream & out, std::pair<format const &, options
     return pretty(out, p.second, p.first);
 }
 
+bool format_pp_eq(format const & f1, format const & f2, options const & o) {
+    std::ostringstream out1;
+    std::ostringstream out2;
+    out1 << mk_pair(f1, o);
+    out2 << mk_pair(f2, o);
+    return out1.str() == out2.str();
+}
+
 format pp(name const & n) {
     return format(n.to_string());
 }

src/util/sexpr/format.h

@@ -318,6 +318,9 @@ format pp(name const & n);
 format pp(sexpr const & s, options const & o);
 format pp(sexpr const & s);
 
+/** \brief Return true iff \c f1 and \c f2 are equal when formatted with options \c o */
+bool format_pp_eq(format const & f1, format const & f2, options const & o);
+
 UDATA_DEFS(format)
 void open_format(lua_State * L);
 }