SI-8512 Infer a type for f"$args"

The f-interpolator gets a type param that better be Any to avoid
unfortunate widenings.

Hey, it worked!

Unfortunately, when `Any` is inferred, `-Xlint:infer-any` takes notice.

This is probably a greater problem for the f-interpolator than for
quasiquotes, which are a more specialized tool.

2 files changed, 14 insertions, 1 deletions

diff --git a/test/files/neg/t7848-interp-warn.flags b/test/files/neg/t7848-interp-warn.flags
index 7949c2afa2..b0d7bc25cb 100644
--- a/test/files/neg/t7848-interp-warn.flags
+++ b/test/files/neg/t7848-interp-warn.flags
@@ -1 +1 @@
--Xlint -Xfatal-warnings
+-Xlint:missing-interpolator -Xfatal-warnings
diff --git a/test/junit/scala/StringContextTest.scala b/test/junit/scala/StringContextTest.scala
index bb0e8c4252..608b82bd96 100644
--- a/test/junit/scala/StringContextTest.scala
+++ b/test/junit/scala/StringContextTest.scala
@@ -62,4 +62,17 @@ class StringContextTest {
     //assertEquals("????", s"????")
     assertEquals("!!!!", s"????") // OK to hijack core interpolator ids
   }
+
+  @Test def fIf() = {
+    val res = f"${if (true) 2.5 else 2.5}%.2f"
+    assertEquals("2.50", res)
+  }
+  @Test def fIfNot() = {
+    val res = f"${if (false) 2.5 else 3.5}%.2f"
+    assertEquals("3.50", res)
+  }
+  @Test def fHeteroArgs() = {
+    val res = f"${3.14}%.2f rounds to ${3}%d"
+    assertEquals("3.14 rounds to 3", res)
+  }
 }