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Add message explaining UNRECOGNIZED cases to UnnecessaryDefaultInEn…
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…umSwitch.

RELNOTES: N/A

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=235818551
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@epmjohnston @ronshapiro
epmjohnston authored and ronshapiro committed Apr 2, 2019
1 parent 39e90c5 commit d3e92a0
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Showing 2 changed files with 129 additions and 52 deletions.
151 changes: 99 additions & 52 deletions core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryDefaultInEnumSwitch.java
View file
Expand Up @@ -23,6 +23,7 @@
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.util.Reachability.canCompleteNormally;

import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.common.collect.Sets.SetView;
import com.google.errorprone.BugPattern;
Expand Down Expand Up @@ -65,16 +66,23 @@ public class UnnecessaryDefaultInEnumSwitch extends BugChecker implements Switch
"Switch handles all enum values: the default case can be omitted to enable enforcement "
+ "at compile-time that the switch statement is exhaustive.";

@Override
public Description matchSwitch(SwitchTree tree, VisitorState state) {
private static final String DESCRIPTION_UNRECOGNIZED =
"Switch handles all enum values except for `UNRECOGNIZED`. The default case can be changed "
+ "to `UNRECOGNIZED` to enable compile-time enforcement that the switch statement is "
+ "exhaustive";

TypeSymbol switchType = ((JCSwitch) tree).getExpression().type.tsym;
@Override
public Description matchSwitch(SwitchTree switchTree, VisitorState state) {
// Only look at enum switches.
TypeSymbol switchType = ((JCSwitch) switchTree).getExpression().type.tsym;
if (switchType.getKind() != ElementKind.ENUM) {
return NO_MATCH;
}

// Extract default case and the one before it.
CaseTree caseBeforeDefault = null;
CaseTree defaultCase = null;
for (CaseTree caseTree : tree.getCases()) {
for (CaseTree caseTree : switchTree.getCases()) {
if (caseTree.getExpression() == null) {
defaultCase = caseTree;
break;
Expand All @@ -85,50 +93,38 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
if (caseBeforeDefault == null || defaultCase == null) {
return NO_MATCH;
}
Set<String> handledCases =
tree.getCases().stream()
.map(CaseTree::getExpression)
.filter(IdentifierTree.class::isInstance)
.map(p -> ((IdentifierTree) p).getName().toString())
.collect(toImmutableSet());
boolean unrecognized = false;
SetView<String> setDifference =
Sets.difference(ASTHelpers.enumValues(switchType), handledCases);
if (!setDifference.isEmpty()) {
if (setDifference.contains("UNRECOGNIZED") && setDifference.size() == 1) {
// if a switch handles all values of an proto-generated enum except for 'UNRECOGNIZED',
// we explicitly handle 'UNRECOGNIZED' and remove the default.
unrecognized = true;
} else {
return NO_MATCH;
}

SetView<String> unhandledCases = unhandledCases(switchTree, switchType);
if (unhandledCases.equals(ImmutableSet.of("UNRECOGNIZED"))) {
// switch handles all values of an proto-generated enum except for 'UNRECOGNIZED'.
return fixUnrecognized(switchTree, defaultCase, state);
}
if (unhandledCases.isEmpty()) {
// switch is exhaustive, remove the default if we can.
return fixDefault(switchTree, caseBeforeDefault, defaultCase, state);
}
// switch is non-exhaustive, default can stay.
return NO_MATCH;
}

private Description fixDefault(
SwitchTree switchTree, CaseTree caseBeforeDefault, CaseTree defaultCase, VisitorState state) {
List<? extends StatementTree> defaultStatements = defaultCase.getStatements();
if (trivialDefault(defaultStatements)) {
// deleting `default:` or `default: break;` is a no-op
SuggestedFix fix =
SuggestedFix.replace(
defaultCase, unrecognized ? "case UNRECOGNIZED: \n // continue below" : "");
return buildDescription(defaultCase)
.setMessage(DESCRIPTION_REMOVED_DEFAULT)
.addFix(fix)
.addFix(SuggestedFix.delete(defaultCase))
.build();
}
String defaultSource =
state
.getSourceCode()
.subSequence(
((JCTree) defaultStatements.get(0)).getStartPosition(),
state.getEndPosition(getLast(defaultStatements)))
.toString();
String initialComments = comments(state, defaultCase, defaultStatements);
if (!canCompleteNormally(tree)) {
String defaultContents = getDefaultCaseContents(defaultCase, defaultStatements, state);
if (!canCompleteNormally(switchTree)) {
// if the switch statement cannot complete normally, then deleting the default
// and moving its statements to after the switch statement is a no-op
SuggestedFix fix =
SuggestedFix.builder()
.replace(defaultCase, unrecognized ? "case UNRECOGNIZED: \n break;" : "")
.postfixWith(tree, initialComments + defaultSource)
.postfixWith(switchTree, defaultContents)
.delete(defaultCase)
.build();
return buildDescription(defaultCase)
.setMessage(DESCRIPTION_MOVED_DEFAULT)
Expand Down Expand Up @@ -173,28 +169,52 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
// it's OK to to delete the default.
return buildDescription(defaultCase)
.setMessage(DESCRIPTION_REMOVED_DEFAULT)
.addFix(
unrecognized
? SuggestedFix.builder()
.replace(defaultCase, "case UNRECOGNIZED:" + initialComments + defaultSource)
.build()
: SuggestedFix.delete(defaultCase))
.addFix(SuggestedFix.delete(defaultCase))
.build();
}
// case (1) -- If it can complete, we need to merge the default into it.
SuggestedFix.Builder fix = SuggestedFix.builder().delete(defaultCase);
if (unrecognized) {
fix.prefixWith(defaultCase, "case UNRECOGNIZED:")
.postfixWith(defaultCase, initialComments + defaultSource);
} else {
fix.postfixWith(caseBeforeDefault, initialComments + defaultSource);
}
fix.postfixWith(caseBeforeDefault, defaultContents);
return buildDescription(defaultCase)
.setMessage(DESCRIPTION_REMOVED_DEFAULT)
.addFix(fix.build())
.build();
}

private Description fixUnrecognized(
SwitchTree switchTree, CaseTree defaultCase, VisitorState state) {
List<? extends StatementTree> defaultStatements = defaultCase.getStatements();
Description.Builder unrecognizedDescription =
buildDescription(defaultCase).setMessage(DESCRIPTION_UNRECOGNIZED);
if (trivialDefault(defaultStatements)) {
// the default case is empty or contains only `break` -- replace it with `case UNRECOGNIZED:`
// with fall out.
SuggestedFix fix =
SuggestedFix.replace(defaultCase, "case UNRECOGNIZED: \n // continue below");
return unrecognizedDescription.addFix(fix).build();
}
String defaultContents = getDefaultCaseContents(defaultCase, defaultStatements, state);
if (!canCompleteNormally(switchTree)) {
// the switch statement cannot complete normally -- replace default with
// `case UNRECOGNIZED: break;` and move content of default case to after the switch tree.
SuggestedFix fix =
SuggestedFix.builder()
.replace(defaultCase, "case UNRECOGNIZED: \n break;")
.postfixWith(switchTree, defaultContents)
.build();
return unrecognizedDescription.addFix(fix).build();
}

SuggestedFix fix = SuggestedFix.replace(defaultCase, "case UNRECOGNIZED:" + defaultContents);
if (!SuggestedFixes.compilesWithFix(fix, state)) {
// code in the default case can't be deleted -- no fix available.
return NO_MATCH;
}

// delete default and move its contents into `UNRECOGNIZED` case.
return unrecognizedDescription.addFix(fix).build();
}

/** Returns true if the default is empty, or contains only a break statement. */
private boolean trivialDefault(List<? extends StatementTree> defaultStatements) {
if (defaultStatements.isEmpty()) {
Expand All @@ -204,9 +224,37 @@ private boolean trivialDefault(List<? extends StatementTree> defaultStatements)
&& getOnlyElement(defaultStatements).getKind() == Tree.Kind.BREAK);
}

private static SetView<String> unhandledCases(SwitchTree tree, TypeSymbol switchType) {
Set<String> handledCases =
tree.getCases().stream()
.map(CaseTree::getExpression)
.filter(IdentifierTree.class::isInstance)
.map(p -> ((IdentifierTree) p).getName().toString())
.collect(toImmutableSet());
return Sets.difference(ASTHelpers.enumValues(switchType), handledCases);
}

private static String getDefaultCaseContents(
CaseTree defaultCase, List<? extends StatementTree> defaultStatements, VisitorState state) {
CharSequence sourceCode = state.getSourceCode();
if (sourceCode == null) {
return "";
}
String defaultSource =
sourceCode
.subSequence(
((JCTree) defaultStatements.get(0)).getStartPosition(),
state.getEndPosition(getLast(defaultStatements)))
.toString();
String initialComments = comments(defaultCase, defaultStatements, sourceCode);
return initialComments + defaultSource;
}

/** Returns the comments between the "default:" case and the first statement within it, if any. */
private String comments(
VisitorState state, CaseTree defaultCase, List<? extends StatementTree> defaultStatements) {
private static String comments(
CaseTree defaultCase,
List<? extends StatementTree> defaultStatements,
CharSequence sourceCode) {
// If there are no statements, then there can be no comments that we strip,
// because comments are attached to the statements, not the "default:" case.
if (defaultStatements.isEmpty()) {
Expand All @@ -217,8 +265,7 @@ private String comments(
// we have no way of identifying the end position of just the "default:" statement.
int defaultStart = ((JCTree) defaultCase).getStartPosition();
int statementStart = ((JCTree) defaultStatements.get(0)).getStartPosition();
String defaultAndComments =
state.getSourceCode().subSequence(defaultStart, statementStart).toString();
String defaultAndComments = sourceCode.subSequence(defaultStart, statementStart).toString();
String comments =
defaultAndComments
.substring(defaultAndComments.indexOf("default:") + "default:".length())
Expand Down
30 changes: 30 additions & 0 deletions core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryDefaultInEnumSwitchTest.java
View file
Expand Up @@ -749,4 +749,34 @@ public void switchCompletesUnrecognized() {
"}")
.doTest(TEXT_MATCH);
}

@Test
public void messages() {
compilationHelper
.addSourceLines(
"Test.java",
"class Test {",
" enum NormalEnum { A, B }",
" enum ProtoEnum { ONE, TWO, UNRECOGNIZED }",
" void normal(NormalEnum e) {",
" switch (e) {",
" case A:",
" case B:",
" // BUG: Diagnostic contains: default case can be omitted",
" default:",
" break;",
" }",
" }",
" void proto(ProtoEnum e) {",
" switch (e) {",
" case ONE:",
" case TWO:",
" // BUG: Diagnostic contains: UNRECOGNIZED",
" default:",
" break;",
" }",
" }",
"}")
.doTest();
}
}

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