Report error on non-tail suspend-calls

It only concerns calls inside another suspend function

 #KT-14924 In Progress

compiler/testData/diagnostics/tests/coroutines/tailCalls/forbidden.kt

@@ -0,0 +1,17 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun nonSuspend() {}
+
+suspend fun foo() {
+    <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { x: Continuation<Int> -> }<!>
+
+    nonSuspend()
+}
+
+suspend fun unitSuspend() {
+    <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { x: Continuation<Int> -> }<!>
+}
+
+suspend fun baz(): Int = run {
+    <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { x: Continuation<Int> -> }<!>
+}

compiler/testData/diagnostics/tests/coroutines/tailCalls/forbidden.txt

@@ -0,0 +1,6 @@
+package
+
+public suspend fun baz(): kotlin.Int
+public suspend fun foo(): kotlin.Unit
+public fun nonSuspend(): kotlin.Unit
+public suspend fun unitSuspend(): kotlin.Unit

compiler/testData/diagnostics/tests/coroutines/tailCalls/localFunctions.kt

@@ -0,0 +1,17 @@
+suspend fun baz() = 1
+suspend fun unit() {}
+
+suspend fun foo() {
+    suspend fun bar() {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE, SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>baz()<!>
+        return unit()
+    }
+
+    suspend fun foobar1(): Int {
+        return baz()
+    }
+
+    suspend fun foobar2() {
+        return unit()
+    }
+}

compiler/testData/diagnostics/tests/coroutines/tailCalls/localFunctions.txt

@@ -0,0 +1,5 @@
+package
+
+public suspend fun baz(): kotlin.Int
+public suspend fun foo(): kotlin.Unit
+public suspend fun unit(): kotlin.Unit

compiler/testData/diagnostics/tests/coroutines/tailCalls/nothingTypedSuspendFunction.kt

@@ -0,0 +1,5 @@
+// Tail calls are not allowed to be Nothing typed. See KT-15051
+suspend fun suspendLogAndThrow(exception: Throwable): Nothing = <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { c ->
+    c.resumeWithException(exception)
+    Suspend
+}<!>

compiler/testData/diagnostics/tests/coroutines/tailCalls/nothingTypedSuspendFunction.txt

@@ -0,0 +1,3 @@
+package
+
+public suspend fun suspendLogAndThrow(/*0*/ exception: kotlin.Throwable): kotlin.Nothing

compiler/testData/diagnostics/tests/coroutines/tailCalls/recursive.kt

@@ -0,0 +1,18 @@
+suspend fun unit1() {
+    <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>unit1()<!>
+}
+
+suspend fun unit2() {
+    return unit2()
+}
+
+suspend fun int1(): Int {
+    return int1()
+}
+
+suspend fun int2(): Int = int2()
+
+suspend fun int3(): Int {
+    <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>int3()<!>
+    return int3()
+}

compiler/testData/diagnostics/tests/coroutines/tailCalls/recursive.txt

@@ -0,0 +1,7 @@
+package
+
+public suspend fun int1(): kotlin.Int
+public suspend fun int2(): kotlin.Int
+public suspend fun int3(): kotlin.Int
+public suspend fun unit1(): kotlin.Unit
+public suspend fun unit2(): kotlin.Unit

compiler/testData/diagnostics/tests/coroutines/tailCalls/tryCatch.kt

@@ -0,0 +1,39 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun nonSuspend() {}
+
+suspend fun baz(): Int = 1
+
+suspend fun tryCatch(): Int {
+    return try {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { x: Continuation<Int> -> }<!>
+    } catch (e: Exception) {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>baz()<!> // another suspend function
+    }
+}
+
+suspend fun tryFinally(): Int {
+    return try {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { x: Continuation<Int> -> }<!>
+    } finally {
+        nonSuspend()
+    }
+}
+
+suspend fun returnInFinally(): Int {
+    try {
+    } finally {
+        // Probably this is too restrictive, but it does not matter much
+        return <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE, SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>baz()<!>
+    }
+}
+
+suspend fun tryCatchFinally(): Int {
+    return try {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>suspendWithCurrentContinuation { x: Continuation<Int> -> }<!>
+    } catch (e: Exception) {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>baz()<!> // another suspend function
+    } finally {
+        <!SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE, SUSPENSION_CALL_MUST_BE_USED_AS_RETURN_VALUE!>baz()<!>
+    }
+}

compiler/testData/diagnostics/tests/coroutines/tailCalls/tryCatch.txt

@@ -0,0 +1,8 @@
+package
+
+public suspend fun baz(): kotlin.Int
+public fun nonSuspend(): kotlin.Unit
+public suspend fun returnInFinally(): kotlin.Int
+public suspend fun tryCatch(): kotlin.Int
+public suspend fun tryCatchFinally(): kotlin.Int
+public suspend fun tryFinally(): kotlin.Int

compiler/testData/diagnostics/tests/coroutines/tailCalls/valid.kt

@@ -0,0 +1,29 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+suspend fun baz() = 1
+
+suspend fun foo() {}
+
+suspend fun bar0() = baz()
+suspend fun bar01(): Int {
+    return baz()
+}
+
+suspend fun bar1() {
+    return if (1.hashCode() > 0) {
+        foo()
+    }
+    else suspendWithCurrentContinuation { x: Continuation<Unit> -> }
+}
+
+suspend fun bar2() =
+        if (1.hashCode() > 0) {
+            foo()
+        }
+        else suspendWithCurrentContinuation { x: Continuation<Unit> -> }
+
+suspend fun bar3() =
+        when {
+            true -> { foo() }
+            else -> suspendWithCurrentContinuation { x: Continuation<Unit> -> }
+        }

compiler/testData/diagnostics/tests/coroutines/tailCalls/valid.txt

@@ -0,0 +1,9 @@
+package
+
+public suspend fun bar0(): kotlin.Int
+public suspend fun bar01(): kotlin.Int
+public suspend fun bar1(): kotlin.Unit
+public suspend fun bar2(): kotlin.Unit
+public suspend fun bar3(): kotlin.Unit
+public suspend fun baz(): kotlin.Int
+public suspend fun foo(): kotlin.Unit