Don't cache dep file

sccache has two modes:
- normal mode
- preprocessor cache mode (aka direct mode in ccache)

In the former case, the preprocessor is invoked and creates the dep file
itself. Whatever sccache does after that is going to overwrite a fresh
file with potentially wrong information, since the cache key is not
indexed on the elements that would affect the contents of the dep file,
resulting in issue #2321.

In the latter case, sccache currently doesn't handle the situation
appropriately (issue #2194), which is why preprocessor cache mode is
automatically disabled when the dependency flags are on the command line
(#2195). Which also means we fallback to the case above.

src/compiler/gcc.rs

@@ -290,7 +290,6 @@ where
     let mut language_extensions = true; // by default, GCC allows extensions
     let mut split_dwarf = false;
     let mut need_explicit_dep_target = false;
-    let mut dep_path = None;
     enum DepArgumentRequirePath {
         NotNeeded,
         Missing,
@@ -382,9 +381,8 @@ where
                 dep_flag = OsString::from(arg.flag_str().expect("Dep target flag expected"));
                 dep_target = Some(s.clone());
             }
-            Some(DepArgumentPath(path)) => {
+            Some(DepArgumentPath(_)) => {
                 need_explicit_dep_argument_path = DepArgumentRequirePath::Provided;
-                dep_path = Some(path.clone());
             }
             Some(SerializeDiagnostics(path)) => {
                 serialize_diagnostics = Some(path.clone());
@@ -644,16 +642,6 @@ where
         dependency_args.push(Path::new(&output).with_extension("d").into_os_string());
     }
 
-    if let Some(path) = dep_path {
-        outputs.insert(
-            "d",
-            ArtifactDescriptor {
-                path: path.clone(),
-                optional: false,
-            },
-        );
-    }
-
     if let Some(path) = serialize_diagnostics {
         outputs.insert(
             "dia",
@@ -1464,13 +1452,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(ovec!["-MF", "foo.o.d"], dependency_args);
@@ -1564,13 +1545,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(ovec!["-MF", "foo.o.d"], dependency_args);
@@ -1606,13 +1580,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(
@@ -1652,13 +1619,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(
@@ -1899,13 +1859,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(

src/compiler/nvcc.rs

@@ -1783,13 +1783,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(

src/compiler/nvhpc.rs

@@ -352,13 +352,6 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
-            ),
-            (
-                "d",
-                ArtifactDescriptor {
-                    path: "foo.o.d".into(),
-                    optional: false
-                }
             )
         );
         assert_eq!(

tests/system.rs

@@ -573,6 +573,56 @@ fn test_compile_with_define(compiler: Compiler, tempdir: &Path) {
         .stderr(predicates::str::contains("warning:").from_utf8().not());
 }
 
+fn test_gcc_clang_depfile(compiler: Compiler, tempdir: &Path) {
+    let Compiler {
+        name,
+        exe,
+        env_vars,
+    } = compiler;
+    println!("test_gcc_clang_depfile: {}", name);
+    copy_to_tempdir(&[INPUT], tempdir);
+    fs::copy(tempdir.join(INPUT), tempdir.join("same-content.c")).unwrap();
+
+    trace!("compile");
+    sccache_command()
+        .args(compile_cmdline(
+            name,
+            exe.clone(),
+            INPUT,
+            OUTPUT,
+            Vec::new(),
+        ))
+        .args(vec_from!(OsString, "-MD", "-MF", "first.d"))
+        .current_dir(tempdir)
+        .envs(env_vars.clone())
+        .assert()
+        .success();
+    sccache_command()
+        .args(compile_cmdline(
+            name,
+            exe,
+            "same-content.c",
+            "same-content.o",
+            Vec::new(),
+        ))
+        .args(vec_from!(OsString, "-MD", "-MF", "second.d"))
+        .current_dir(tempdir)
+        .envs(env_vars)
+        .assert()
+        .success();
+    let mut first = String::new();
+    let mut second = String::new();
+    File::open(tempdir.join("first.d"))
+        .unwrap()
+        .read_to_string(&mut first)
+        .unwrap();
+    File::open(tempdir.join("second.d"))
+        .unwrap()
+        .read_to_string(&mut second)
+        .unwrap();
+    assert_ne!(first, second);
+}
+
 fn run_sccache_command_tests(compiler: Compiler, tempdir: &Path, preprocessor_cache_mode: bool) {
     if compiler.name != "clang++" {
         test_basic_compile(compiler.clone(), tempdir);
@@ -589,6 +639,7 @@ fn run_sccache_command_tests(compiler: Compiler, tempdir: &Path, preprocessor_ca
     if compiler.name == "clang" || compiler.name == "gcc" {
         test_gcc_clang_no_warnings_from_macro_expansion(compiler.clone(), tempdir);
         test_split_dwarf_object_generate_output_dir_changes(compiler.clone(), tempdir);
+        test_gcc_clang_depfile(compiler.clone(), tempdir);
     }
     if compiler.name == "clang++" {
         test_clang_multicall(compiler.clone(), tempdir);