Print pattern strings of anonymous pattern on conflict messages

2 files changed, 28 insertions, 10 deletions

diff --git a/grammar/grammar.go b/grammar/grammar.go
index a43b133..353beef 100644
--- a/grammar/grammar.go
+++ b/grammar/grammar.go
@@ -17,6 +17,7 @@ type astActionEntry struct {
 type Grammar struct {
 	lexSpec              *mlspec.LexSpec
 	skipLexKinds         []mlspec.LexKind
+	sym2AnonPat          map[symbol]string
 	productionSet        *productionSet
 	augmentedStartSymbol symbol
 	symbolTable          *symbolTable
@@ -47,6 +48,7 @@ func (b *GrammarBuilder) Build(root *spec.RootNode) (*Grammar, error) {
 	return &Grammar{
 		lexSpec:              symTabAndLexSpec.lexSpec,
 		skipLexKinds:         symTabAndLexSpec.skip,
+		sym2AnonPat:          symTabAndLexSpec.sym2AnonPat,
 		productionSet:        prodsAndActs.prods,
 		augmentedStartSymbol: prodsAndActs.augStartSym,
 		symbolTable:          symTabAndLexSpec.symTab,
@@ -57,6 +59,7 @@ func (b *GrammarBuilder) Build(root *spec.RootNode) (*Grammar, error) {
 type symbolTableAndLexSpec struct {
 	symTab      *symbolTable
 	anonPat2Sym map[string]symbol
+	sym2AnonPat map[symbol]string
 	lexSpec     *mlspec.LexSpec
 	skip        []mlspec.LexKind
 }
@@ -95,6 +98,7 @@ func (b *GrammarBuilder) genSymbolTableAndLexSpec(root *spec.RootNode) (*symbolT
 	}
 
 	anonPat2Sym := map[string]symbol{}
+	sym2AnonPat := map[symbol]string{}
 	var anonEntries []*mlspec.LexEntry
 	{
 		anonPats := []string{}
@@ -127,6 +131,7 @@ func (b *GrammarBuilder) genSymbolTableAndLexSpec(root *spec.RootNode) (*symbolT
 				return nil, err
 			}
 			anonPat2Sym[p] = sym
+			sym2AnonPat[sym] = p
 
 			anonEntries = append(anonEntries, &mlspec.LexEntry{
 				Kind:    mlspec.LexKind(kind),
@@ -160,6 +165,7 @@ func (b *GrammarBuilder) genSymbolTableAndLexSpec(root *spec.RootNode) (*symbolT
 	return &symbolTableAndLexSpec{
 		symTab:      symTab,
 		anonPat2Sym: anonPat2Sym,
+		sym2AnonPat: sym2AnonPat,
 		lexSpec: &mlspec.LexSpec{
 			Entries: entries,
 		},
@@ -494,6 +500,7 @@ func Compile(gram *Grammar) (*spec.CompiledGrammar, error) {
 		termCount:    len(terms),
 		nonTermCount: len(nonTerms),
 		symTab:       gram.symbolTable,
+		sym2AnonPat:  gram.sym2AnonPat,
 	}
 	tab, err := slr.build()
 	if err != nil {
diff --git a/grammar/slr.go b/grammar/slr.go
index 3794ab7..221bf8f 100644
--- a/grammar/slr.go
+++ b/grammar/slr.go
@@ -170,6 +170,7 @@ type slrTableBuilder struct {
 	termCount    int
 	nonTermCount int
 	symTab       *symbolTable
+	sym2AnonPat  map[symbol]string
 }
 
 func (b *slrTableBuilder) build() (*ParsingTable, error) {
@@ -229,17 +230,9 @@ func (b *slrTableBuilder) build() (*ParsingTable, error) {
 			fmt.Fprintf(&msg, "\n")
 			switch c := conflict.(type) {
 			case *shiftReduceConflict:
-				sym, ok := b.symTab.toText(c.sym)
-				if !ok {
-					sym = fmt.Sprintf("<not found: %v>", c.sym)
-				}
-				fmt.Fprintf(&msg, "%v: shift/reduce conflict (shift %v, reduce %v) on %v", c.state, c.nextState, c.prodNum, sym)
+				fmt.Fprintf(&msg, "%v: shift/reduce conflict (shift %v, reduce %v) on %v", c.state, c.nextState, c.prodNum, b.symbolToText(c.sym))
 			case *reduceReduceConflict:
-				sym, ok := b.symTab.toText(c.sym)
-				if !ok {
-					sym = fmt.Sprintf("<not found: %v>", c.sym)
-				}
-				fmt.Fprintf(&msg, "%v: reduce/reduce conflict (reduce %v and %v) on %v", c.state, c.prodNum1, c.prodNum2, sym)
+				fmt.Fprintf(&msg, "%v: reduce/reduce conflict (reduce %v and %v) on %v", c.state, c.prodNum1, c.prodNum2, b.symbolToText(c.sym))
 			}
 		}
 		return nil, fmt.Errorf("%v conflicts:%v", len(conflicts), msg.String())
@@ -247,3 +240,21 @@ func (b *slrTableBuilder) build() (*ParsingTable, error) {
 
 	return ptab, nil
 }
+
+func (b *slrTableBuilder) symbolToText(sym symbol) string {
+	text, ok := b.symTab.toText(sym)
+	if !ok {
+		return fmt.Sprintf("<symbol not found: %v>", sym)
+	}
+
+	if strings.HasPrefix(text, "_") {
+		pat, ok := b.sym2AnonPat[sym]
+		if !ok {
+			return fmt.Sprintf("<pattern not found: %v>", text)
+		}
+
+		return fmt.Sprintf(`"%v"`, pat)
+	}
+
+	return text
+}