fix: Diagnose recursion when resolving expressions (#2264)

Author: technohippy

src/resolver.ts

@@ -996,6 +996,9 @@ export class Resolver extends DiagnosticEmitter {
     return null;
   }
 
+  /** resolving expressions */
+  private resolvingExpressions: Set<Expression> = new Set();
+
   /** Resolves an expression to its static type. */
   resolveExpression(
     /** The expression to resolve. */
@@ -1006,6 +1009,21 @@ export class Resolver extends DiagnosticEmitter {
     ctxType: Type = Type.auto,
     /** How to proceed with eventual diagnostics. */
     reportMode: ReportMode = ReportMode.REPORT
+  ): Type | null {
+    const resolvingExpressions = this.resolvingExpressions;
+    if (resolvingExpressions.has(node)) return null;
+    resolvingExpressions.add(node);
+    const resolved = this.doResolveExpression(node, ctxFlow, ctxType, reportMode);
+    resolvingExpressions.delete(node);
+    return resolved;
+  }
+
+  /** Resolves an expression to its static type. (may cause stack overflow) */
+  private doResolveExpression(
+    node: Expression,
+    ctxFlow: Flow,
+    ctxType: Type = Type.auto,
+    reportMode: ReportMode = ReportMode.REPORT
   ): Type | null {
     while (node.kind == NodeKind.PARENTHESIZED) { // skip
       node = (<ParenthesizedExpression>node).expression;

tests/compiler/avoid-resolve-loop.json

@@ -0,0 +1,10 @@
+{
+  "asc_flags": [
+  ],
+  "stderr": [
+    "AS225: Expression cannot be represented by a type.",
+    "TS2448: Variable 'avoid-resolve-loop/e' used before its declaration.",
+    "TS2322: Type 'void' is not assignable to type '<auto>'.",
+    "AS225: Expression cannot be represented by a type."
+  ]
+}

tests/compiler/avoid-resolve-loop.ts

@@ -0,0 +1,4 @@
+let a = a[0];
+
+let e = e;
+typeof [e];