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Add rule to report discouraged comment locations (#1365)
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Autocorrect is not implemented. This is an error which only
happens rarely. Its value is that it makes implementation of
some rules way easier when comment do not have to be taken
into account.

Initial implementation just contains one single discouraged
location. More will follow when implementing the rule to
rewrite the function signature automatically as is described
in #1341.
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paul-dingemans authored Mar 9, 2022
1 parent 14c0adf commit ec1f3f3
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -25,6 +25,7 @@ Please welcome [paul-dingemans](https://github.com/paul-dingemans) as an officia
- Basic tests for CLI ([#540](https://github.com/pinterest/ktlint/issues/540))
- Add experimental rule for unexpected spaces in a type reference before a function identifier (`function-type-reference-spacing`) ([#1341](https://github.com/pinterest/ktlint/issues/1341))
- Add experimental rule for unnecessary parentheses in function call followed by lambda ([#1068](https://github.com/pinterest/ktlint/issues/1068))
- Add experimental rule to detect discouraged comment locations (`discouraged-comment-location`) ([#1365](https://github.com/pinterest/ktlint/pull/1365))
- Add rule to check spacing after fun keyword (`fun-keyword-spacing`) ([#1362](https://github.com/pinterest/ktlint/pull/1362))
- Add experimental rules for unnecessary spacing between modifiers in and after the last modifier in a modifier list ([#1361](https://github.com/pinterest/ktlint/pull/1361))

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1 change: 1 addition & 0 deletions README.md
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Expand Up @@ -77,6 +77,7 @@ by passing the `--experimental` flag to `ktlint`.

- `experimental:annotation`: Annotation formatting - multiple annotations should be on a separate line than the annotated declaration; annotations with parameters should each be on separate lines; annotations should be followed by a space
- `experimental:argument-list-wrapping`: Argument list wrapping
- `experimental:discouraged-comment-location`: Detect discouraged comment locations (no autocorrect)
- `experimental:enum-entry-name-case`: Enum entry names should be uppercase underscore-separated names
- `experimental:multiline-if-else`: Braces required for multiline if/else statements
- `experimental:no-empty-first-line-in-method-block`: No leading empty lines in method blocks
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@@ -0,0 +1,51 @@
package com.pinterest.ktlint.ruleset.experimental

import com.pinterest.ktlint.core.Rule
import com.pinterest.ktlint.core.ast.ElementType.TYPE_PARAMETER_LIST
import com.pinterest.ktlint.core.ast.isPartOfComment
import com.pinterest.ktlint.core.ast.prevCodeSibling
import org.jetbrains.kotlin.com.intellij.lang.ASTNode

/**
* The AST allows comments to be placed anywhere. This however can lead to code which is unnecessarily hard to read.
* Disallowing comments at certain positions in the AST makes development of a rule easier as they have not to be taken
* into account in that rule.
*
* In examples below, a comment is placed between a type parameter list and the function name. Such comments are badly
* handled by default IntelliJ IDEA code formatter. We should put no effort in making and keeping ktlint in sync with
* such bad code formatting.
*
* ```
* fun <T>
* // some comment
* foo(t: T) = "some-result"
*
* fun <T>
* /* some comment
* *
* */
* foo(t: T) = "some-result"
* ```
*/
public class DiscouragedCommentLocationRule : Rule("discouraged-comment-location") {
override fun visit(
node: ASTNode,
autoCorrect: Boolean,
emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
) {
node
.takeIf { it.isPartOfComment() }
?.prevCodeSibling()
?.let { codeSiblingBeforeComment ->
// Be restrictive when adding new locations at which comments are discouraged. Always run against major
// open source projects first to verify whether valid cases are found to comment at this location.
if (codeSiblingBeforeComment.elementType == TYPE_PARAMETER_LIST) {
emit(
node.startOffset,
"No comment expected at this location",
false
)
}
}
}
}
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Expand Up @@ -22,6 +22,7 @@ public class ExperimentalRuleSetProvider : RuleSetProvider {
SpacingAroundUnaryOperatorRule(),
AnnotationSpacingRule(),
UnnecessaryParenthesesBeforeTrailingLambdaRule(),
DiscouragedCommentLocationRule(),
FunKeywordSpacingRule(),
FunctionTypeReferenceSpacingRule(),
ModifierListSpacingRule()
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package com.pinterest.ktlint.ruleset.experimental

import com.pinterest.ktlint.core.LintError
import com.pinterest.ktlint.test.format
import com.pinterest.ktlint.test.lint
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test

class DiscouragedCommentLocationTest {
@Test
fun `Given an EOL comment after a type parameter then report a discouraged comment location`() {
val code =
"""
fun <T> // some comment
foo(t: T) = "some-result"
""".trimIndent()
assertThat(DiscouragedCommentLocationRule().lint(code)).containsExactly(
LintError(1, 9, "discouraged-comment-location", "No comment expected at this location")
)
assertThat(DiscouragedCommentLocationRule().format(code)).isEqualTo(code)
}

@Test
fun `Given an EOL comment on a newline after a type parameter then report a discouraged comment location`() {
val code =
"""
fun <T>
// some comment
foo(t: T) = "some-result"
""".trimIndent()
assertThat(DiscouragedCommentLocationRule().lint(code)).containsExactly(
LintError(2, 1, "discouraged-comment-location", "No comment expected at this location")
)
assertThat(DiscouragedCommentLocationRule().format(code)).isEqualTo(code)
}

@Test
fun `Given a block comment after a type parameter then report a discouraged comment location`() {
val code =
"""
fun <T> /* some comment */
foo(t: T) = "some-result"
""".trimIndent()
assertThat(DiscouragedCommentLocationRule().lint(code)).containsExactly(
LintError(1, 9, "discouraged-comment-location", "No comment expected at this location")
)
assertThat(DiscouragedCommentLocationRule().format(code)).isEqualTo(code)
}

@Test
fun `Given a block comment on a newline after a type parameter then report a discouraged comment location`() {
val code =
"""
fun <T>
/* some comment */
foo(t: T) = "some-result"
""".trimIndent()
assertThat(DiscouragedCommentLocationRule().lint(code)).containsExactly(
LintError(2, 1, "discouraged-comment-location", "No comment expected at this location")
)
assertThat(DiscouragedCommentLocationRule().format(code)).isEqualTo(code)
}

@Test
fun `Given a KDOC comment after a type parameter then report a discouraged comment location`() {
val code =
"""
fun <T> /** some comment */
foo(t: T) = "some-result"
""".trimIndent()
assertThat(DiscouragedCommentLocationRule().lint(code)).containsExactly(
LintError(1, 9, "discouraged-comment-location", "No comment expected at this location")
)
assertThat(DiscouragedCommentLocationRule().format(code)).isEqualTo(code)
}

@Test
fun `Given a KDOC comment on a newline after a type parameter then report a discouraged comment location`() {
val code =
"""
fun <T>
/**
* some comment
*/
foo(t: T) = "some-result"
""".trimIndent()
assertThat(DiscouragedCommentLocationRule().lint(code)).containsExactly(
LintError(2, 1, "discouraged-comment-location", "No comment expected at this location")
)
assertThat(DiscouragedCommentLocationRule().format(code)).isEqualTo(code)
}
}

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