Allow coalescing through trivia

I also noticed that `lexQuantifier` could silently
eat trivia if it failed to lex a quantification,
so also fix that.

Author: hamishknight

Sources/_RegexParser/Regex/Parse/LexicalAnalysis.swift

@@ -480,35 +480,37 @@ extension Parser {
   ///
   mutating func lexQuantifier(
   ) -> (Located<Quant.Amount>, Located<Quant.Kind>, [AST.Trivia])? {
-    var trivia: [AST.Trivia] = []
+    tryEating { p in
+      var trivia: [AST.Trivia] = []
 
-    if let t = lexNonSemanticWhitespace() { trivia.append(t) }
+      if let t = p.lexNonSemanticWhitespace() { trivia.append(t) }
 
-    let amt: Located<Quant.Amount>? = recordLoc { p in
-      if p.tryEat("*") { return .zeroOrMore }
-      if p.tryEat("+") { return .oneOrMore }
-      if p.tryEat("?") { return .zeroOrOne }
+      let amt: Located<Quant.Amount>? = p.recordLoc { p in
+        if p.tryEat("*") { return .zeroOrMore }
+        if p.tryEat("+") { return .oneOrMore }
+        if p.tryEat("?") { return .zeroOrOne }
 
-      return p.tryEating { p in
-        guard p.tryEat("{"),
-              let range = p.lexRange(trivia: &trivia),
-              p.tryEat("}")
-        else { return nil }
-        return range.value
+        return p.tryEating { p in
+          guard p.tryEat("{"),
+                let range = p.lexRange(trivia: &trivia),
+                p.tryEat("}")
+          else { return nil }
+          return range.value
+        }
       }
-    }
-    guard let amt = amt else { return nil }
+      guard let amt = amt else { return nil }
 
-    // PCRE allows non-semantic whitespace here in extended syntax mode.
-    if let t = lexNonSemanticWhitespace() { trivia.append(t) }
+      // PCRE allows non-semantic whitespace here in extended syntax mode.
+      if let t = p.lexNonSemanticWhitespace() { trivia.append(t) }
 
-    let kind: Located<Quant.Kind> = recordLoc { p in
-      if p.tryEat("?") { return .reluctant  }
-      if p.tryEat("+") { return .possessive }
-      return .eager
-    }
+      let kind: Located<Quant.Kind> = p.recordLoc { p in
+        if p.tryEat("?") { return .reluctant  }
+        if p.tryEat("+") { return .possessive }
+        return .eager
+      }
 
-    return (amt, kind, trivia)
+      return (amt, kind, trivia)
+    }
   }
 
   /// Try to consume a range, returning `nil` if unsuccessful.

Sources/_StringProcessing/ByteCodeGen.swift

@@ -812,6 +812,10 @@ fileprivate extension Compiler.ByteCodeGen {
           current.append(lhs)
           rangeOperands.append(String(rhs))
           return true
+        case .trivia:
+          // Trivia can be completely ignored if we've already coalesced
+          // something.
+          return !current.isEmpty
         default:
           return false
         }
@@ -927,6 +931,10 @@ fileprivate extension Compiler.ByteCodeGen {
         case .quotedLiteral(let q):
           str += q
           return true
+        case .trivia:
+          // Trivia can be completely ignored if we've already coalesced
+          // something.
+          return !str.isEmpty
         default:
           return false
         }

Sources/_StringProcessing/PrintAsPattern.swift

@@ -304,6 +304,10 @@ extension PrettyPrinter {
         case .quotedLiteral(let q):
           literal.append(q)
           return true
+        case .trivia:
+          // Trivia can be completely ignored if we've already coalesced
+          // something.
+          return !literal.isEmpty
         default:
           return false
         }

Tests/RegexTests/MatchTests.swift

@@ -345,6 +345,23 @@ extension RegexTests {
       input: "e\u{301}0e\u{302}",
       match: "e\u{301}0e\u{302}"
     )
+    firstMatchTest(
+      #"(?x) e \u{35C} \u{315}(?#hello)\u{301}"#,
+      input: "e\u{301}\u{315}\u{35C}",
+      match: "e\u{301}\u{315}\u{35C}"
+    )
+    firstMatchTest(
+      #"(?x) e \u{35C} \u{315 301}"#,
+      input: "e\u{301}\u{315}\u{35C}",
+      match: "e\u{301}\u{315}\u{35C}"
+    )
+
+    // We don't coalesce across groups.
+    firstMatchTests(
+      #"e\u{301}(?:\u{315}\u{35C})?"#,
+      ("e\u{301}", "e\u{301}"),
+      ("e\u{301}\u{315}\u{35C}", nil)
+    )
 
     // Escape sequences that represent scalar values.
     firstMatchTest(#"\a[\b]\e\f\n\r\t"#,
@@ -824,6 +841,30 @@ extension RegexTests {
       ("e\u{301}\u{315}\u{35C}", "e\u{301}\u{315}\u{35C}"),
       ("e\u{35C}\u{301}\u{315}", "e\u{35C}\u{301}\u{315}")
     )
+    firstMatchTests(
+      #"(?x) [ e \u{315} \u{301} \u{35C} ]"#,
+      ("e", nil),
+      ("e\u{315}", nil),
+      ("e\u{301}", nil),
+      ("e\u{315}\u{301}\u{35C}", "e\u{315}\u{301}\u{35C}"),
+      ("e\u{301}\u{315}\u{35C}", "e\u{301}\u{315}\u{35C}"),
+      ("e\u{35C}\u{301}\u{315}", "e\u{35C}\u{301}\u{315}")
+    )
+
+    // We don't coalesce across character classes.
+    firstMatchTests(
+      #"e[\u{315}\u{301}\u{35C}]"#,
+      ("e", nil),
+      ("e\u{315}", nil),
+      ("e\u{315}\u{301}", nil),
+      ("e\u{301}\u{315}\u{35C}", nil)
+    )
+    firstMatchTests(
+      #"[e[\u{301}]]"#,
+      ("e", "e"),
+      ("\u{301}", "\u{301}"),
+      ("e\u{301}", nil)
+    )
 
     firstMatchTests(
       #"[a-z1\u{E9}-\u{302}\u{E1}3-59]"#,
@@ -982,6 +1023,16 @@ extension RegexTests {
       ("e\u{302}", nil),
       ("e\u{303}", "e\u{303}"))
 
+    firstMatchTests(
+      #"(?x) [ e \u{301} [ e \u{303} ] -- [ [ e \u{301} ] e \u{302} ] ]"#,
+      ("e", nil),
+      ("\u{301}", nil),
+      ("\u{302}", nil),
+      ("\u{303}", nil),
+      ("e\u{301}", nil),
+      ("e\u{302}", nil),
+      ("e\u{303}", "e\u{303}"))
+
     firstMatchTest("[-]", input: "123-abcxyz", match: "-")
 
     // These are metacharacters in certain contexts, but normal characters
@@ -2152,6 +2203,11 @@ extension RegexTests {
       #"\u{65 301}"#,
       (eComposed, true),
       (eDecomposed, true))
+
+    matchTest(
+      #"(?x) \u{65} \u{301}"#,
+      (eComposed, true),
+      (eDecomposed, true))
   }
 
   func testCanonicalEquivalenceCharacterClass() throws {

Tests/RegexTests/RenderDSLTests.swift

@@ -177,6 +177,18 @@ extension RenderDSLTests {
       }
       """#)
 
+    try testConversion(#"(?x) a \u{301}"#, #"""
+      Regex {
+        "a\u{301}"
+      }
+      """#)
+
+    try testConversion(#"(?x) [ a b c \u{301} ] "#, #"""
+      Regex {
+        One(.anyOf("abc\u{301}"))
+      }
+      """#)
+
     try testConversion(#"👨\u{200D}👨\u{200D}👧\u{200D}👦"#, #"""
       Regex {
         "👨\u{200D}👨\u{200D}👧\u{200D}👦"