Auto merge of #7257 - RobMor:no-spaces-between-flags, r=alexcrichton

Fix #7217: Add support for rustc-flags without spaces between flags and values

Hi, I believe this pull request contains a fix for issue #7217. This is my first pull request to any open source project, much less any Rust project. I'm not super familiar with Rust at the moment, so let me know if I should change anything. Also any help/advice you can give me about this PR would be much appreciated!

I do have some specific questions:
- Is the test I added worthy of being its own test? I basically copied the one above it and remove the spaces between the flags and the values. Should I have added on to the test above it instead?
- Would it be better if I directly unit-tested this function in some other test file?
- Is the `ureachable!` macro good style?

src/cargo/core/compiler/custom_build.rs

@@ -514,29 +514,38 @@ impl BuildOutput {
             .split(|c: char| c.is_whitespace())
             .filter(|w| w.chars().any(|c| !c.is_whitespace()));
         let (mut library_paths, mut library_links) = (Vec::new(), Vec::new());
+
         while let Some(flag) = flags_iter.next() {
-            if flag != "-l" && flag != "-L" {
+            if flag.starts_with("-l") || flag.starts_with("-L") {
+                // Check if this flag has no space before the value as is
+                // common with tools like pkg-config
+                // e.g. -L/some/dir/local/lib or -licui18n
+                let (flag, mut value) = flag.split_at(2);
+                if value.len() == 0 {
+                    value = match flags_iter.next() {
+                        Some(v) => v,
+                        None => failure::bail! {
+                            "Flag in rustc-flags has no value in {}: {}",
+                            whence,
+                            value
+                        },
+                    }
+                }
+
+                match flag {
+                    "-l" => library_links.push(value.to_string()),
+                    "-L" => library_paths.push(PathBuf::from(value)),
+
+                    // This was already checked above
+                    _ => unreachable!(),
+                };
+            } else {
                 failure::bail!(
                     "Only `-l` and `-L` flags are allowed in {}: `{}`",
                     whence,
                     value
                 )
             }
-            let value = match flags_iter.next() {
-                Some(v) => v,
-                None => failure::bail!(
-                    "Flag in rustc-flags has no value in {}: `{}`",
-                    whence,
-                    value
-                ),
-            };
-            match flag {
-                "-l" => library_links.push(value.to_string()),
-                "-L" => library_paths.push(PathBuf::from(value)),
-
-                // was already checked above
-                _ => failure::bail!("only -l and -L flags are allowed"),
-            };
         }
         Ok((library_paths, library_links))
     }

tests/testsuite/build_script.rs

@@ -254,6 +254,65 @@ fn custom_build_script_rustc_flags() {
         .run();
 }
 
+#[cargo_test]
+fn custom_build_script_rustc_flags_no_space() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+
+            name = "bar"
+            version = "0.5.0"
+            authors = ["wycats@example.com"]
+
+            [dependencies.foo]
+            path = "foo"
+        "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .file(
+            "foo/Cargo.toml",
+            r#"
+            [project]
+
+            name = "foo"
+            version = "0.5.0"
+            authors = ["wycats@example.com"]
+            build = "build.rs"
+        "#,
+        )
+        .file("foo/src/lib.rs", "")
+        .file(
+            "foo/build.rs",
+            r#"
+            fn main() {
+                println!("cargo:rustc-flags=-lnonexistinglib -L/dummy/path1 -L/dummy/path2");
+            }
+        "#,
+        )
+        .build();
+
+    p.cargo("build --verbose")
+        .with_stderr(
+            "\
+[COMPILING] foo [..]
+[RUNNING] `rustc --crate-name build_script_build foo/build.rs [..]
+[RUNNING] `[..]build-script-build`
+[RUNNING] `rustc --crate-name foo foo/src/lib.rs [..]\
+    -L dependency=[CWD]/target/debug/deps \
+    -L /dummy/path1 -L /dummy/path2 -l nonexistinglib`
+[COMPILING] bar [..]
+[RUNNING] `rustc --crate-name bar src/main.rs [..]\
+    -L dependency=[CWD]/target/debug/deps \
+    --extern foo=[..]libfoo-[..] \
+    -L /dummy/path1 -L /dummy/path2`
+[FINISHED] dev [..]
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn links_no_build_cmd() {
     let p = project()