Support running all available patch checks

The `BaseErrorProneJavaCompiler` [supports](https://github.com/google/error-prone/blob/master/check_api/src/main/java/com/google/errorprone/BaseErrorProneJavaCompiler.java#L225) running _all_ patch checks; it just requires that one doesn't provide any explicitly named checkers.

In practice this doesn't work, however, because:
- `PatchingOptions` [requires](https://github.com/google/error-prone/blob/master/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java#L142) a named checker or a custom refactorer.
- Specifying `-XepPatchChecks:` without any explicit check will [cause](https://github.com/google/error-prone/blob/master/check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java#L404) the empty string to be stored as a named checker.

This PR proposes to resolve the above issues by:
1. Requiring `-XepPatchLocation` when `-XepPatchChecks` is specified, but not vice versa.
2. Omitting empty strings from `-XepPatchChecks:`.

Fixes google#947

COPYBARA_INTEGRATE_REVIEW=google#947 from PicnicSupermarket:bugfix/support-empty-PatchChecks c5d9125
PiperOrigin-RevId: 565064731

check_api/src/main/java/com/google/errorprone/ErrorProneOptions.java

@@ -140,21 +140,7 @@ abstract static class Builder {
 
       abstract Builder importOrganizer(ImportOrganizer importOrganizer);
 
-      abstract PatchingOptions autoBuild();
-
-      final PatchingOptions build() {
-
-        PatchingOptions patchingOptions = autoBuild();
-
-        // If anything is specified, then (checkers or refaster) and output must be set.
-        if ((!patchingOptions.namedCheckers().isEmpty()
-                || patchingOptions.customRefactorer().isPresent())
-            ^ patchingOptions.doRefactor()) {
-          throw new InvalidCommandLineOptionException(
-              "-XepPatchChecks and -XepPatchLocation must be specified together");
-        }
-        return patchingOptions;
-      }
+      abstract PatchingOptions build();
     }
   }
 
@@ -419,6 +405,8 @@ public static ErrorProneOptions processArgs(Iterable<String> args) {
      * You can pass the IGNORE_UNKNOWN_CHECKS_FLAG to opt-out of that checking.  This allows you to
      * use command lines from different versions of error-prone interchangeably.
      */
+    boolean patchLocationSet = false;
+    boolean patchCheckSet = false;
     Builder builder = new Builder();
     for (String arg : args) {
       switch (arg) {
@@ -458,6 +446,7 @@ public static ErrorProneOptions processArgs(Iterable<String> args) {
           } else if (arg.startsWith(ErrorProneFlags.PREFIX)) {
             builder.parseFlag(arg);
           } else if (arg.startsWith(PATCH_OUTPUT_LOCATION)) {
+            patchLocationSet = true;
             String remaining = arg.substring(PATCH_OUTPUT_LOCATION.length());
             if (remaining.equals("IN_PLACE")) {
               builder.patchingOptionsBuilder().inPlace(true);
@@ -468,6 +457,7 @@ public static ErrorProneOptions processArgs(Iterable<String> args) {
               builder.patchingOptionsBuilder().baseDirectory(remaining);
             }
           } else if (arg.startsWith(PATCH_CHECKS_PREFIX)) {
+            patchCheckSet = true;
             String remaining = arg.substring(PATCH_CHECKS_PREFIX.length());
             if (remaining.startsWith("refaster:")) {
               // Refaster rule, load from InputStream at file
@@ -485,7 +475,8 @@ public static ErrorProneOptions processArgs(Iterable<String> args) {
                         }
                       });
             } else {
-              Iterable<String> checks = Splitter.on(',').trimResults().split(remaining);
+              Iterable<String> checks =
+                  Splitter.on(',').trimResults().omitEmptyStrings().split(remaining);
               builder.patchingOptionsBuilder().namedCheckers(ImmutableSet.copyOf(checks));
             }
           } else if (arg.startsWith(PATCH_IMPORT_ORDER_PREFIX)) {
@@ -505,6 +496,11 @@ public static ErrorProneOptions processArgs(Iterable<String> args) {
       }
     }
 
+    if (patchCheckSet && !patchLocationSet) {
+      throw new InvalidCommandLineOptionException(
+          "-XepPatchLocation must be specified when -XepPatchChecks is");
+    }
+
     return builder.build(remainingArgs.build());
   }
 

check_api/src/test/java/com/google/errorprone/ErrorProneOptionsTest.java

@@ -238,9 +238,6 @@ public void recognizesPatch() {
 
   @Test
   public void throwsExceptionWithBadPatchArgs() {
-    assertThrows(
-        InvalidCommandLineOptionException.class,
-        () -> ErrorProneOptions.processArgs(new String[] {"-XepPatchLocation:IN_PLACE"}));
     assertThrows(
         InvalidCommandLineOptionException.class,
         () ->
@@ -257,6 +254,24 @@ public void recognizesRefaster() {
     assertThat(options.patchingOptions().customRefactorer()).isPresent();
   }
 
+  @Test
+  public void understandsEmptySetOfNamedCheckers() {
+    ErrorProneOptions options =
+        ErrorProneOptions.processArgs(new String[] {"-XepPatchLocation:IN_PLACE"});
+    assertThat(options.patchingOptions().doRefactor()).isTrue();
+    assertThat(options.patchingOptions().inPlace()).isTrue();
+    assertThat(options.patchingOptions().namedCheckers()).isEmpty();
+    assertThat(options.patchingOptions().customRefactorer()).isAbsent();
+
+    options =
+        ErrorProneOptions.processArgs(
+            new String[] {"-XepPatchLocation:IN_PLACE", "-XepPatchChecks:"});
+    assertThat(options.patchingOptions().doRefactor()).isTrue();
+    assertThat(options.patchingOptions().inPlace()).isTrue();
+    assertThat(options.patchingOptions().namedCheckers()).isEmpty();
+    assertThat(options.patchingOptions().customRefactorer()).isAbsent();
+  }
+
   @Test
   public void importOrder_staticFirst() {
     ErrorProneOptions options =