8043251: Bogus javac error: required: no arguments, found: no arguments

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java

@@ -4173,17 +4173,34 @@ JCDiagnostic getDiagnostic(JCDiagnostic.DiagnosticType dkind,
 
             Pair<Symbol, JCDiagnostic> c = errCandidate();
             Symbol ws = c.fst.asMemberOf(site, types);
-            return diags.create(dkind, log.currentSource(), pos,
-                      "cant.apply.symbol",
-                      compactMethodDiags ?
-                              d -> MethodResolutionDiagHelper.rewrite(diags, pos, log.currentSource(), dkind, c.snd) : null,
-                      kindName(ws),
-                      ws.name == names.init ? ws.owner.name : ws.name,
-                      methodArguments(ws.type.getParameterTypes()),
-                      methodArguments(argtypes),
-                      kindName(ws.owner),
-                      ws.owner.type,
-                      c.snd);
+
+            // If the problem is due to type arguments, then the method parameters aren't relevant,
+            // so use the error message that omits them to avoid confusion.
+            switch (c.snd.getCode()) {
+                case "compiler.misc.wrong.number.type.args":
+                case "compiler.misc.explicit.param.do.not.conform.to.bounds":
+                    return diags.create(dkind, log.currentSource(), pos,
+                              "cant.apply.symbol.noargs",
+                              compactMethodDiags ?
+                                      d -> MethodResolutionDiagHelper.rewrite(diags, pos, log.currentSource(), dkind, c.snd) : null,
+                              kindName(ws),
+                              ws.name == names.init ? ws.owner.name : ws.name,
+                              kindName(ws.owner),
+                              ws.owner.type,
+                              c.snd);
+                default:
+                    return diags.create(dkind, log.currentSource(), pos,
+                              "cant.apply.symbol",
+                              compactMethodDiags ?
+                                      d -> MethodResolutionDiagHelper.rewrite(diags, pos, log.currentSource(), dkind, c.snd) : null,
+                              kindName(ws),
+                              ws.name == names.init ? ws.owner.name : ws.name,
+                              methodArguments(ws.type.getParameterTypes()),
+                              methodArguments(argtypes),
+                              kindName(ws.owner),
+                              ws.owner.type,
+                              c.snd);
+            }
         }
 
         @Override

src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties

@@ -233,6 +233,11 @@ compiler.err.switch.expression.no.result.expressions=\
 compiler.err.call.must.be.first.stmt.in.ctor=\
     call to {0} must be first statement in constructor
 
+# 0: symbol kind, 1: name, 2: symbol kind, 3: type, 4: message segment
+compiler.err.cant.apply.symbol.noargs=\
+    {0} {1} in {2} {3} cannot be applied to given types;\n\
+    reason: {4}
+
 # 0: symbol kind, 1: name, 2: list of type or message segment, 3: list of type or message segment, 4: symbol kind, 5: type, 6: message segment
 compiler.err.cant.apply.symbol=\
     {0} {1} in {4} {5} cannot be applied to given types;\n\

test/langtools/tools/javac/Diagnostics/8043251/T8043251.java

@@ -0,0 +1,10 @@
+/**
+ * @test /nodynamiccopyright/
+ * @bug     8043251
+ * @summary Confusing error message with wrong number of type parameters
+ * @compile/fail/ref=T8043251.out -XDrawDiagnostics T8043251.java
+ */
+import java.util.function.Function;
+class T8043251 {
+    Function<String, String> f = Function.<String, String>identity();
+}

test/langtools/tools/javac/Diagnostics/8043251/T8043251.out

@@ -0,0 +1,2 @@
+T8043251.java:9:42: compiler.err.cant.apply.symbol.noargs: kindname.method, identity, kindname.interface, java.util.function.Function<T,R>, (compiler.misc.wrong.number.type.args: 1)
+1 error

test/langtools/tools/javac/diags/examples/ExplicitParamsDoNotConformToBounds.java

@@ -21,7 +21,7 @@
  * questions.
  */
 
-// key: compiler.err.cant.apply.symbol
+// key: compiler.err.cant.apply.symbol.noargs
 // key: compiler.misc.explicit.param.do.not.conform.to.bounds
 
 class ExplicitParamsDoNotConformToBounds {

test/langtools/tools/javac/diags/examples/WrongNumberTypeArgsFragment.java

@@ -21,7 +21,7 @@
  * questions.
  */
 
-// key: compiler.err.cant.apply.symbol
+// key: compiler.err.cant.apply.symbol.noargs
 // key: compiler.misc.wrong.number.type.args
 
 import java.util.*;