Add DateTimeExampleStringCheck ErrorProne plugin

mug-errorprone/BUILD

@@ -10,6 +10,7 @@ java_library(
         "@maven//:com_google_errorprone_error_prone_check_api",
         "@maven//:com_google_guava_guava",
         "//mug:base",
+        "//mug:time",
         "//mug-guava",
     ],
 )
@@ -66,6 +67,7 @@ junit_tests(
     deps = [
         ":errorprone",
         "//mug:format",
+        "//mug:time",
         "//mug-guava:safe_sql",
         "@maven//:com_google_guava_guava",
         "@maven//:com_google_guava_guava_testlib",

mug-errorprone/src/main/java/com/google/mu/errorprone/DateTimeExampleStringCheck.java

@@ -0,0 +1,44 @@
+package com.google.mu.errorprone;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+
+import com.google.auto.service.AutoService;
+import com.google.mu.time.DateTimeFormats;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.BugPattern.LinkType;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.MethodInvocationTree;
+
+/** Validate the example datetime string passed to {@code DateTimeFormats.formatOf()}. */
+@BugPattern(
+    summary = "Checks that the format string passed to DateTimeFormats.formatOf() is supported.",
+    link = "go/java-tips/024#safer-string-format-reuse",
+    linkType = LinkType.CUSTOM,
+    severity = ERROR)
+@AutoService(BugChecker.class)
+public final class DateTimeExampleStringCheck extends AbstractBugChecker
+    implements AbstractBugChecker.MethodInvocationCheck {
+  private static final Matcher<ExpressionTree> MATCHER =
+      staticMethod().onClass("com.google.mu.time.DateTimeFormats").named("formatOf");
+
+  @Override
+  public void checkMethodInvocation(MethodInvocationTree tree, VisitorState state)
+      throws ErrorReport {
+    if (!MATCHER.matches(tree, state) || tree.getArguments().isEmpty()) {
+      return;
+    }
+    ExpressionTree exampleArg = tree.getArguments().get(0);
+    String exampleString = ASTHelpers.constValue(exampleArg, String.class);
+    checkingOn(exampleArg).require(exampleString != null, "compile-time string constant expected");
+    try {
+      Object verified = DateTimeFormats.formatOf(exampleString);
+    } catch (IllegalArgumentException e) {
+      throw checkingOn(exampleArg).report(e.getMessage());
+    }
+  }
+}

mug-errorprone/src/test/java/com/google/mu/errorprone/DateTimeExampleStringCheckTest.java

@@ -0,0 +1,27 @@
+package com.google.mu.errorprone;
+
+import com.google.errorprone.CompilationTestHelper;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public final class DateTimeExampleStringCheckTest {
+  private final CompilationTestHelper helper =
+      CompilationTestHelper.newInstance(DateTimeExampleStringCheck.class, getClass());
+
+  @Test
+  public void mmddyyNotSupported() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            "import static com.google.mu.time.DateTimeFormats.formatOf;",
+            "import java.time.format.DateTimeFormatter;",
+            "class Test {",
+            "  private static final DateTimeFormatter FORMAT = formatOf(",
+            "      // BUG: Diagnostic contains: unsupported date time example: 10/20/2023",
+            "      \"10/20/2023 10:10:10\");",
+            "}")
+        .doTest();
+  }
+}

mug/BUILD

@@ -5,6 +5,7 @@ java_library(
         "src/main/java/com/google/mu/util/*.java",
         "src/main/java/com/google/mu/util/stream/*.java",
         "src/main/java/com/google/mu/function/*.java",
+        "src/main/java/com/google/mu/collect/*.java",
       ],
       exclude = ["src/main/java/com/google/mu/util/StringFormat.java"]),
 )
@@ -31,6 +32,14 @@ java_library(
     exported_plugins = ["//mug-errorprone:plugin"],
 )
 
+java_library(
+    name = "time",
+    visibility = ["//visibility:public"],
+    srcs = glob(["src/main/java/com/google/mu/time/*.java"]),
+    deps = [":base"],
+    exported_plugins = ["//mug-errorprone:plugin"],
+)
+
 load("@com_googlesource_gerrit_bazlets//tools:junit.bzl", "junit_tests")
 
 java_library(

mug/src/main/java/com/google/mu/time/DateTimeFormats.java

@@ -245,7 +245,7 @@ static DateTimeFormatter inferFromExample(String example) {
                 DateTimeFormatter fmt = DateTimeFormatter.ofPattern(pattern);
                 fmt.parse(example);
                 return fmt;
-              } catch (DateTimeParseException | IllegalArgumentException e) {
+              } catch (DateTimeParseException e) {
                 throw new IllegalArgumentException(
                     "invalid date time example: " + example + " (" + pattern + ")", e);
               }
@@ -280,7 +280,7 @@ private static String inferDateTimePattern(String example, List<?> signature) {
                   })
               .orElse(0);
       if (consumed <= 0) {
-        throw new IllegalArgumentException("unsupported example: " + example);
+        throw new IllegalArgumentException("unsupported date time example: " + example);
       }
       matched += consumed;
     }