From 93a327b9f4eee0da0c91129af8495259447e0cc9 Mon Sep 17 00:00:00 2001
From: Kevin Mehall <km@kevinmehall.net>
Date: Mon, 15 Feb 2021 10:32:54 -0700
Subject: [PATCH] Restore support for `[^ ]` inverted pattern syntax.

---
 peg-macros/translate.rs   | 28 +++++++++-------------------
 src/lib.rs                |  7 +++++--
 tests/run-pass/pattern.rs | 12 ++++++++++++
 3 files changed, 26 insertions(+), 21 deletions(-)
 create mode 100644 tests/run-pass/pattern.rs

diff --git a/peg-macros/translate.rs b/peg-macros/translate.rs
index cbb5db4..87b07ea 100644
--- a/peg-macros/translate.rs
+++ b/peg-macros/translate.rs
@@ -343,15 +343,6 @@ fn labeled_seq(context: &Context, exprs: &[TaggedExpr], inner: TokenStream) -> T
     })
 }
 
-fn cond_swap<T>(swap: bool, tup: (T, T)) -> (T, T) {
-    let (a, b) = tup;
-    if swap {
-        (b, a)
-    } else {
-        (a, b)
-    }
-}
-
 fn compile_expr(context: &Context, e: &Expr, result_used: bool) -> TokenStream {
     match e {
         LiteralExpr(ref s) => {
@@ -363,17 +354,16 @@ fn compile_expr(context: &Context, e: &Expr, result_used: bool) -> TokenStream {
         }
 
         PatternExpr(ref pattern_group) => {
-            let invert = false;
-            let pattern = pattern_group.stream();
-            let pat_str = pattern.to_string();
+            let pat_str = pattern_group.to_string();
 
-            let (in_set, not_in_set) = cond_swap(
-                invert,
-                (
-                    quote! { ::peg::RuleResult::Matched(__next, ()) },
-                    quote! { __err_state.mark_failure(__pos, #pat_str) },
-                ),
-            );
+            let success_res = quote! { ::peg::RuleResult::Matched(__next, ()) };
+            let failure_res = quote! { __err_state.mark_failure(__pos, #pat_str) };
+
+            let (pattern, in_set, not_in_set) = if let Some(pattern) = group_check_prefix(pattern_group, '^') {
+                (pattern, failure_res, success_res)
+            } else {
+                (pattern_group.stream(), success_res, failure_res)
+            };
 
             let in_set_arm = quote!( #pattern => #in_set, );
 
diff --git a/src/lib.rs b/src/lib.rs
index be1be86..5e8a846 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -63,7 +63,9 @@
 //!
 //!   * `"keyword"` - _Literal:_ match a literal string.
 //!   * `['0'..='9']`  - _Pattern:_ match a single element that matches a Rust `match`-style
-//!     pattern. [(details)](#match-expressions)
+//!     pattern. [(details)](#pattern-expressions)
+//!   * `[^ '0'..='9']`  - _Inverted pattern:_ match a single element that does not match a Rust `match`-style
+//!     pattern. [(details)](#pattern-expressions)
 //!   * `some_rule()` - _Rule:_ match a rule defined elsewhere in the grammar and return its
 //!     result. Arguments in the parentheses are Rust expressions.
 //!   * `_` or `__` or `___` - _Rule (underscore):_ As a special case, rule names
@@ -130,7 +132,8 @@
 //!
 //! The `[pat]` syntax expands into a [Rust `match`
 //! pattern](https://doc.rust-lang.org/book/ch18-03-pattern-syntax.html) against the next character
-//! (or element) of the input.
+//! (or element) of the input. When the pattern begins with `^`, the matching behavior is inverted:
+//! the expression succeeds only if the pattern does *not* match.
 //!
 //! To match sets of characters, use Rust's `..=` inclusive range pattern
 //! syntax and `|` to match multiple patterns. For example `['a'..='z' | 'A'..='Z']` matches an
diff --git a/tests/run-pass/pattern.rs b/tests/run-pass/pattern.rs
new file mode 100644
index 0000000..c3fadc7
--- /dev/null
+++ b/tests/run-pass/pattern.rs
@@ -0,0 +1,12 @@
+peg::parser!( grammar test() for str {
+    pub rule alphanumeric() = ['a'..='z' | 'A'..='Z' | '0'..='9']*
+    pub rule inverted_pat() -> &'input str = "(" s:$([^')']*) ")" {s}
+});
+
+fn main() {
+    assert!(test::alphanumeric("azAZ09").is_ok());
+    assert!(test::alphanumeric("@").is_err());
+
+    assert_eq!(test::inverted_pat("(asdf)"), Ok("asdf"));
+}
+