throw error when paths option mapping empty array

src/compiler/diagnosticMessages.json

@@ -2336,6 +2336,10 @@
         "category": "Error",
         "code": 5065
     },
+    "Substitutions for pattern '{0}' shouldn't be an empty array.": {
+        "category": "Error",
+        "code": 5066
+    },
     "Concatenate and emit output to single file.": {
         "category": "Message",
         "code": 6001
@@ -2800,11 +2804,11 @@
         "category": "Error",
         "code": 6133
     },
-    "Report errors on unused locals.": {
+    "Report errors on unused locals.": {
         "category": "Message",
         "code": 6134
     },
-    "Report errors on unused parameters.": {
+    "Report errors on unused parameters.": {
         "category": "Message",
         "code": 6135
     },

src/compiler/program.ts

@@ -2200,6 +2200,9 @@ namespace ts {
                         programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Pattern_0_can_have_at_most_one_Asterisk_character, key));
                     }
                     if (isArray(options.paths[key])) {
+                        if (options.paths[key].length === 0) {
+                            programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Substitutions_for_pattern_0_shouldn_t_be_an_empty_array, key));
+                        }
                         for (const subst of options.paths[key]) {
                             const typeOfSubst = typeof subst;
                             if (typeOfSubst === "string") {

tests/baselines/reference/pathsValidation3.errors.txt

@@ -0,0 +1,6 @@
+error TS5066: Substitutions for pattern 'foo' shouldn't be an empty array.
+
+
+!!! error TS5066: Substitutions for pattern 'foo' shouldn't be an empty array.
+==== tests/cases/compiler/a.ts (0 errors) ====
+    let x = 1;

tests/baselines/reference/pathsValidation3.js

@@ -0,0 +1,5 @@
+//// [a.ts]
+let x = 1;
+
+//// [a.js]
+var x = 1;

tests/cases/compiler/pathsValidation3.ts

@@ -0,0 +1,12 @@
+// @filename: tsconfig.json
+{
+    "compilerOptions": {
+        "baseUrl": ".",
+        "paths": {
+            "foo": []
+        }
+    }
+}
+
+// @filename: a.ts
+let x = 1;