Parser: better syntax error prediction

nois-lang · Jun 5, 2023 · 3a83943 · 3a83943
1 parent 4628c76
commit 3a83943
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Showing 3 changed files with 5 additions and 8 deletions.
diff --git a/data/test.no b/data/test.no
diff --git a/src/location.ts b/src/location.ts
@@ -37,6 +37,7 @@ export const prettyIndex = (index: number, source: Source): string => {
     const highlight = ' '.repeat(start.column) + '^'
     const lineNum = `${start.line + 1} | `
     return `\
+    
 ${lineNum}${line}
 ${' '.repeat(lineNum.length)}${highlight}`
 }

diff --git a/src/parser/parser.ts b/src/parser/parser.ts
@@ -56,18 +56,19 @@ export const rules: Map<ParserTokenName, Rule> = new Map(rawRules.map((r: Rule)
 export const parse = (tokens: LexerToken[], node: TokenName = 'program', index: number = 0): Token | SyntaxErrorInfo | true => {
     const rule = rules.get(<ParserTokenName>node)!
     if (rule) {
-        const errorInfos: SyntaxErrorInfo[] = []
+        let syntaxError: SyntaxErrorInfo | undefined
         for (const branch of rule.branches) {
             if (isEmptyBranch(branch)) return true
             const transform = { name: <ParserTokenName>node, branch }
             const branchToken = parseTransform(transform, tokens, index)
             if ('name' in branchToken) {
                 return branchToken
             } else {
-                errorInfos.push(branchToken)
+                if (branchToken.location.start > (syntaxError?.location.start ?? -1))
+                    syntaxError = branchToken
             }
         }
-        return errorInfos.at(-1)!
+        return syntaxError!
     } else {
         const error = { expect: [node], got: tokens[index].name, location: tokens[index].location }
         return node === tokens[index].name ? tokens[index] : error