Add a test case for incremental + codegen-units interaction.

src/test/codegen-units/partitioning/incremental-merging.rs

@@ -0,0 +1,42 @@
+// ignore-tidy-linelength
+// We specify -C incremental here because we want to test the partitioning for
+// incremental compilation
+// compile-flags:-Zprint-mono-items=lazy -Cincremental=tmp/partitioning-tests/incremental-merging
+// compile-flags:-Ccodegen-units=3
+
+#![crate_type = "rlib"]
+
+// This test makes sure that merging of CGUs works together with incremental
+// compilation but at the same time does not modify names of CGUs that were not
+// affected by merging.
+//
+// We expect CGUs `aaa` and `bbb` to be merged (because they are the smallest),
+// while `ccc` and `ddd` are supposed to stay untouched.
+
+pub mod aaa {
+    //~ MONO_ITEM fn incremental_merging::aaa[0]::foo[0] @@ incremental_merging-aaa--incremental_merging-bbb[External]
+    pub fn foo(a: u64) -> u64 {
+        a + 1
+    }
+}
+
+pub mod bbb {
+    //~ MONO_ITEM fn incremental_merging::bbb[0]::foo[0] @@ incremental_merging-aaa--incremental_merging-bbb[External]
+    pub fn foo(a: u64, b: u64) -> u64 {
+        a + b + 1
+    }
+}
+
+pub mod ccc {
+    //~ MONO_ITEM fn incremental_merging::ccc[0]::foo[0] @@ incremental_merging-ccc[External]
+    pub fn foo(a: u64, b: u64, c: u64) -> u64 {
+        a + b + c + 1
+    }
+}
+
+pub mod ddd {
+    //~ MONO_ITEM fn incremental_merging::ddd[0]::foo[0] @@ incremental_merging-ddd[External]
+    pub fn foo(a: u64, b: u64, c: u64, d: u64) -> u64 {
+        a + b + c + d + 1
+    }
+}

src/tools/compiletest/src/runtest.rs

@@ -2517,7 +2517,7 @@ impl<'test> TestCx<'test> {
                     .filter(|s| !s.is_empty())
                     .map(|s| {
                         if cgu_has_crate_disambiguator {
-                            remove_crate_disambiguator_from_cgu(s)
+                            remove_crate_disambiguators_from_set_of_cgu_names(s)
                         } else {
                             s.to_string()
                         }
@@ -2567,6 +2567,16 @@ impl<'test> TestCx<'test> {
 
             new_name
         }
+
+        // The name of merged CGUs is constructed as the names of the original
+        // CGUs joined with "--". This function splits such composite CGU names
+        // and handles each component individually.
+        fn remove_crate_disambiguators_from_set_of_cgu_names(cgus: &str) -> String {
+            cgus.split("--")
+                .map(|cgu| remove_crate_disambiguator_from_cgu(cgu))
+                .collect::<Vec<_>>()
+                .join("--")
+        }
     }
 
     fn init_incremental_test(&self) {