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[PATCH 5/5] c++: demonstrate custom error messages in the examples
From: |
Akim Demaille |
Subject: |
[PATCH 5/5] c++: demonstrate custom error messages in the examples |
Date: |
Sun, 12 Sep 2021 12:05:49 +0200 |
Let's use c++/glr to demonstrate custom error messages in C++ (not
just in glr2.cc).
* examples/c++/glr/c++-types.yy (report_syntax_error): New.
* examples/c++/glr/c++-types.test: Adjust.
* examples/c/bistromathic/parse.y: Comment changes.
* tests/local.at (AT_YYERROR_DEFINE(c++)): Use a nicer way to print
the lookakead's name.
---
examples/c++/README.md | 9 +++++++
examples/c++/glr/README.md | 3 +++
examples/c++/glr/c++-types.test | 2 +-
examples/c++/glr/c++-types.yy | 43 ++++++++++++++++++++++++++++++---
examples/c/bistromathic/parse.y | 5 ++--
tests/local.at | 7 ++----
6 files changed, 58 insertions(+), 11 deletions(-)
diff --git a/examples/c++/README.md b/examples/c++/README.md
index 93cd09d5..dff3783e 100644
--- a/examples/c++/README.md
+++ b/examples/c++/README.md
@@ -39,6 +39,15 @@ examples.
Extracted from the documentation: [A Complete C++
Example](https://www.gnu.org/software/bison/manual/html_node/A-Complete-C_002b_002b-Example.html).
+## glr
+
+This example demonstrates the use of GLR parsers to handle (local)
+ambiguities in the C++ language. See the node "Merging GLR Parses" in
+Bison's documentation.
+
+It uses (Bison) variants to store objects as semantic values. It also
+demonstrates custom error messages in C++.
+
<!---
Local Variables:
diff --git a/examples/c++/glr/README.md b/examples/c++/glr/README.md
index 26067c27..ed06a0c6 100644
--- a/examples/c++/glr/README.md
+++ b/examples/c++/glr/README.md
@@ -4,6 +4,9 @@ This example demonstrates the use of GLR parsers to handle
(local)
ambiguities in the C++ language. See the node "Merging GLR Parses" in
Bison's documentation.
+It uses (Bison) variants to store objects as semantic values. It also
+demonstrates custom error messages in C++.
+
<!---
Local Variables:
fill-column: 76
diff --git a/examples/c++/glr/c++-types.test b/examples/c++/glr/c++-types.test
index 7440ea24..db5be8d7 100644
--- a/examples/c++/glr/c++-types.test
+++ b/examples/c++/glr/c++-types.test
@@ -47,4 +47,4 @@ run 0 "\
5.0-13: <OR>(<init-declare>(T, y, +(z, q)), =(<cast>(y, T), +(z, q)))
7.0-15: <error>
9.0-5: +(z, q)
-err: 7.5: syntax error, unexpected identifier, expecting = or + or )"
+err: 7.5: syntax error on token identifier (expected = or + or ))"
diff --git a/examples/c++/glr/c++-types.yy b/examples/c++/glr/c++-types.yy
index fa8889de..a3131b05 100644
--- a/examples/c++/glr/c++-types.yy
+++ b/examples/c++/glr/c++-types.yy
@@ -27,8 +27,8 @@
%locations
%debug
-// Nice error messages with details.
-%define parse.error detailed
+// Custom error messages.
+%define parse.error custom
%code requires
{
@@ -44,9 +44,11 @@
#include <fstream>
#include <cstring>
+ // Merge two semantic values.
static Node
stmt_merge (const Node& x0, const Node& x1);
+ // Fetch a token.
static yy::parser::symbol_type
yylex ();
}
@@ -100,13 +102,41 @@ declarator
std::istream* input = nullptr;
yy::parser::location_type loc;
-// An error reporting function.
+
+/*---------.
+| Parser. |
+`---------*/
+
+// Generate a custom error message.
+void
+yy::parser::report_syntax_error (const context& ctx) const
+{
+ std::cerr << ctx.location () << ": syntax error";
+ if (!ctx.lookahead ().empty ())
+ std::cerr << " on token " << ctx.lookahead ().name ();
+ {
+ enum { TOKENMAX = 10 };
+ symbol_kind_type expected[TOKENMAX];
+ int n = ctx.expected_tokens (expected, TOKENMAX);
+ if (0 < n)
+ {
+ for (int i = 0; i < n; ++i)
+ std::cerr << (i == 0 ? " (expected " : " or ")
+ << symbol_name (expected[i]);
+ std::cerr << ')';
+ }
+ }
+ std::cerr << '\n';
+}
+
+// Report the error to the user.
void
yy::parser::error (const location_type& l, const std::string& m)
{
std::cerr << l << ": " << m << '\n';
}
+// Fetch the next token.
static yy::parser::symbol_type
yylex ()
{
@@ -168,12 +198,19 @@ yylex ()
}
}
+// Merge two semantic values as an AST including both alternatives.
static Node
stmt_merge (const Node& x0, const Node& x1)
{
return Nterm ("<OR>", x0, x1);
}
+
+/*-------.
+| Main. |
+`-------*/
+
+// Parse `file` using parser `parse`.
int
process (yy::parser& parse, const std::string& file)
{
diff --git a/examples/c/bistromathic/parse.y b/examples/c/bistromathic/parse.y
index e06db523..8b1591e6 100644
--- a/examples/c/bistromathic/parse.y
+++ b/examples/c/bistromathic/parse.y
@@ -465,8 +465,9 @@ yyreport_syntax_error (const yypcontext_t *ctx, const
user_context *uctx)
}
-// Called by yyparse on error.
-void yyerror (const YYLTYPE *loc, const user_context *uctx, char const
*format, ...)
+// Called by yyparse on errors to report the error to the user.
+void
+yyerror (const YYLTYPE *loc, const user_context *uctx, char const *format, ...)
{
if (uctx->silent)
return;
diff --git a/tests/local.at b/tests/local.at
index 170e5da1..1138df47 100644
--- a/tests/local.at
+++ b/tests/local.at
@@ -823,11 +823,8 @@ m4_define([AT_YYERROR_DEFINE(c++)],
++*nerrs;]])[]AT_LOCATION_IF([[
std::cerr << ctx.location () << ": ";]])[
std::cerr << "syntax error";
- {
- symbol_kind_type la = ctx.token ();
- if (la != symbol_kind::S_YYEMPTY)
- std::cerr << " on token [" << symbol_name (la) << ']';
- }
+ if (!ctx.lookahead ().empty ())
+ std::cerr << " on token [" << ctx.lookahead ().name () << ']';
{
enum { TOKENMAX = 10 };
symbol_kind_type expected[TOKENMAX];
--
2.32.0