Allow unknown type annotation on catch clause variable

src/compiler/checker.ts

@@ -7688,7 +7688,7 @@ namespace ts {
             // Handle catch clause variables
             const declaration = symbol.valueDeclaration;
             if (isCatchClauseVariableDeclarationOrBindingElement(declaration)) {
-                return anyType;
+                return tryGetTypeFromEffectiveTypeNode(declaration) === unknownType ? unknownType : anyType;
             }
             // Handle export default expressions
             if (isSourceFile(declaration) && isJsonSourceFile(declaration)) {
@@ -32140,7 +32140,7 @@ namespace ts {
             if (catchClause) {
                 // Grammar checking
                 if (catchClause.variableDeclaration) {
-                    if (catchClause.variableDeclaration.type) {
+                    if (catchClause.variableDeclaration.type && tryGetTypeFromEffectiveTypeNode(catchClause.variableDeclaration) !== unknownType) {
                         grammarErrorOnFirstToken(catchClause.variableDeclaration.type, Diagnostics.Catch_clause_variable_cannot_have_a_type_annotation);
                     }
                     else if (catchClause.variableDeclaration.initializer) {

tests/baselines/reference/catchClauseWithUnknownTypeAnnotation.js

@@ -0,0 +1,19 @@
+//// [catchClauseWithUnknownTypeAnnotation.ts]
+try {
+} catch (e: unknown) {
+}
+type UnknownAlias = unknown;
+try {
+} catch (e: UnknownAlias) {
+}
+
+
+//// [catchClauseWithUnknownTypeAnnotation.js]
+try {
+}
+catch (e) {
+}
+try {
+}
+catch (e) {
+}

tests/baselines/reference/catchClauseWithUnknownTypeAnnotation.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/compiler/catchClauseWithUnknownTypeAnnotation.ts ===
+try {
+} catch (e: unknown) {
+>e : Symbol(e, Decl(catchClauseWithUnknownTypeAnnotation.ts, 1, 9))
+}
+type UnknownAlias = unknown;
+>UnknownAlias : Symbol(UnknownAlias, Decl(catchClauseWithUnknownTypeAnnotation.ts, 2, 1))
+
+try {
+} catch (e: UnknownAlias) {
+>e : Symbol(e, Decl(catchClauseWithUnknownTypeAnnotation.ts, 5, 9))
+>UnknownAlias : Symbol(UnknownAlias, Decl(catchClauseWithUnknownTypeAnnotation.ts, 2, 1))
+}
+

tests/baselines/reference/catchClauseWithUnknownTypeAnnotation.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/catchClauseWithUnknownTypeAnnotation.ts ===
+try {
+} catch (e: unknown) {
+>e : unknown
+}
+type UnknownAlias = unknown;
+>UnknownAlias : unknown
+
+try {
+} catch (e: UnknownAlias) {
+>e : unknown
+}
+

tests/cases/compiler/catchClauseWithUnknownTypeAnnotation.ts

@@ -0,0 +1,7 @@
+try {
+} catch (e: unknown) {
+}
+type UnknownAlias = unknown;
+try {
+} catch (e: UnknownAlias) {
+}