Exhaustive when on boolean argument. A set of tests.

Compile-time constants are taken into account. #KT-3743 Fixed.

compiler/testData/diagnostics/tests/when/ExhaustiveBoolean.kt

@@ -0,0 +1,8 @@
+// See also: KT-3743
+fun foo(arg: Boolean): String {
+    // Must be exhaustive
+    return when(arg) {
+        true -> "truth"
+        false -> "falsehood"
+    }
+}

compiler/testData/diagnostics/tests/when/ExhaustiveBoolean.txt

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+package
+
+internal fun foo(/*0*/ arg: kotlin.Boolean): kotlin.String

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanBrackets.kt

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+fun foo(arg: Boolean): String {
+    // Must be exhaustive
+    return when(arg) {
+        (true) -> "truth"
+        ((false)) -> "falsehood"
+    }
+}

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanBrackets.txt

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+package
+
+internal fun foo(/*0*/ arg: kotlin.Boolean): kotlin.String

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanComplex.kt

@@ -0,0 +1,8 @@
+// See also: KT-3743
+fun foo(arg: Boolean): String {
+    // Must be exhaustive
+    return when(arg) {
+        2 == 2 -> "truth"
+        2 == 1 -> "falsehood"
+    }
+}

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanComplex.txt

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+package
+
+internal fun foo(/*0*/ arg: kotlin.Boolean): kotlin.String

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanNullable.kt

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+// See also: KT-3743
+fun foo(arg: Boolean?): String {
+    // Must be exhaustive
+    return when(arg) {
+        true -> "truth"
+        false -> "falsehood"
+        null -> "unknown"
+    }
+}

compiler/testData/diagnostics/tests/when/ExhaustiveBooleanNullable.txt

@@ -0,0 +1,3 @@
+package
+
+internal fun foo(/*0*/ arg: kotlin.Boolean?): kotlin.String

compiler/testData/diagnostics/tests/when/NonExhaustiveBooleanNullable.kt

@@ -0,0 +1,8 @@
+// See also: KT-3743
+fun foo(arg: Boolean?): String {
+    // Must be NOT exhaustive
+    return <!NO_ELSE_IN_WHEN!>when<!>(arg) {
+        true -> "truth"
+        false -> "falsehood"
+    }
+}

compiler/testData/diagnostics/tests/when/NonExhaustiveBooleanNullable.txt

@@ -0,0 +1,3 @@
+package
+
+internal fun foo(/*0*/ arg: kotlin.Boolean?): kotlin.String