buildRustCrate: add heuristic to picking the right source files

Cargo has a few odd (old) ways of picking source files if the `bin.path`
attribute isn't given in the Cargo.toml. This commit adds support for
some of those. The previous behaviour always defaulted to `src/main.rs`
which was not always the right choice.

Since there is  look-ahead into the unpacked sources before running the
actual builder the path selection logic has to be embedded within the
build script.

`buildRustCrate` currently supports two ways of running building
binaries when processing a crate:

- Explicit definition of all the binaries (& optionally the paths to
their respective `main.rs`) and,
- if not binary was explictly configured all files matching the patterns
  `src/main.rs`, `src/bin/*.rs`.

When the explicit list is given without path information paths are now
being picked from a list of candidates. The first match wins. The order
is the same as within the cargo compatibility code.

If the crate does not provide any libraries the path `src/{bin_name}.rs`
is also considered.

All underscores within the binary names are translated into dashes (`-`)
before the lookups are made. This seems to be a common convention.

1 files changed, 159 insertions, 0 deletions

diff --git a/pkgs/build-support/rust/build-rust-crate/build-crate.nix b/pkgs/build-support/rust/build-rust-crate/build-crate.nix
new file mode 100644
index 000000000000..748d48edefc2
--- /dev/null
+++ b/pkgs/build-support/rust/build-rust-crate/build-crate.nix
@@ -0,0 +1,159 @@
+{ lib, stdenv, echo_build_heading, noisily, makeDeps }:
+{ crateName,
+  dependencies,
+  crateFeatures, libName, release, libPath,
+  crateType, metadata, crateBin, finalBins,
+  extraRustcOpts, verbose, colors }:
+
+  let
+
+    deps = makeDeps dependencies;
+        rustcOpts =
+          lib.lists.foldl' (opts: opt: opts + " " + opt)
+            (if release then "-C opt-level=3" else "-C debuginfo=2")
+            (["-C codegen-units=1"] ++ extraRustcOpts);
+        rustcMeta = "-C metadata=${metadata} -C extra-filename=-${metadata}";
+  in ''
+    runHook preBuild
+    norm=""
+    bold=""
+    green=""
+    boldgreen=""
+    if [[ "${colors}" == "always" ]]; then
+      norm="$(printf '\033[0m')" #returns to "normal"
+      bold="$(printf '\033[0;1m')" #set bold
+      green="$(printf '\033[0;32m')" #set green
+      boldgreen="$(printf '\033[0;1;32m')" #set bold, and set green.
+    fi
+    ${echo_build_heading colors}
+    ${noisily colors verbose}
+
+    build_lib() {
+       lib_src=$1
+       echo_build_heading $lib_src ${libName}
+
+       noisily rustc --crate-name $CRATE_NAME $lib_src --crate-type ${crateType} \
+         ${rustcOpts} ${rustcMeta} ${crateFeatures} --out-dir target/lib \
+         --emit=dep-info,link -L dependency=target/deps ${deps} --cap-lints allow \
+         $BUILD_OUT_DIR $EXTRA_BUILD $EXTRA_FEATURES --color ${colors}
+
+       EXTRA_LIB=" --extern $CRATE_NAME=target/lib/lib$CRATE_NAME-${metadata}.rlib"
+       if [ -e target/deps/lib$CRATE_NAME-${metadata}${stdenv.hostPlatform.extensions.sharedLibrary} ]; then
+          EXTRA_LIB="$EXTRA_LIB --extern $CRATE_NAME=target/lib/lib$CRATE_NAME-${metadata}${stdenv.hostPlatform.extensions.sharedLibrary}"
+       fi
+    }
+
+    build_bin() {
+      crate_name=$1
+      crate_name_=$(echo $crate_name | sed -e "s/-/_/g")
+      main_file=""
+      if [[ ! -z $2 ]]; then
+        main_file=$2
+      fi
+      echo_build_heading $@
+      noisily rustc --crate-name $crate_name_ $main_file --crate-type bin ${rustcOpts}\
+        ${crateFeatures} --out-dir target/bin --emit=dep-info,link -L dependency=target/deps \
+        $LINK ${deps}$EXTRA_LIB --cap-lints allow \
+        $BUILD_OUT_DIR $EXTRA_BUILD $EXTRA_FEATURES --color ${colors}
+      if [ "$crate_name_" != "$crate_name" ]; then
+        mv target/bin/$crate_name_ target/bin/$crate_name
+      fi
+    }
+
+
+    EXTRA_LIB=""
+    CRATE_NAME=$(echo ${libName} | sed -e "s/-/_/g")
+
+    if [[ -e target/link_ ]]; then
+      EXTRA_BUILD="$(cat target/link_) $EXTRA_BUILD"
+    fi
+
+    if [[ -e "${libPath}" ]]; then
+       build_lib ${libPath}
+    elif [[ -e src/lib.rs ]]; then
+       build_lib src/lib.rs
+    elif [[ -e src/${libName}.rs ]]; then
+       build_lib src/${libName}.rs
+    fi
+
+    echo "$EXTRA_LINK_SEARCH" | while read i; do
+       if [[ ! -z "$i" ]]; then
+         for lib in $i; do
+           echo "-L $lib" >> target/link
+           L=$(echo $lib | sed -e "s#$(pwd)/target/build#$out/lib#")
+           echo "-L $L" >> target/link.final
+         done
+       fi
+    done
+    echo "$EXTRA_LINK" | while read i; do
+       if [[ ! -z "$i" ]]; then
+         for lib in $i; do
+           echo "-l $lib" >> target/link
+           echo "-l $lib" >> target/link.final
+         done
+       fi
+    done
+
+    if [[ -e target/link ]]; then
+       sort -u target/link.final > target/link.final.sorted
+       mv target/link.final.sorted target/link.final
+       sort -u target/link > target/link.sorted
+       mv target/link.sorted target/link
+
+       tr '\n' ' ' < target/link > target/link_
+       LINK=$(cat target/link_)
+    fi
+
+    mkdir -p target/bin
+    printf "%s\n" "${crateBin}" | head -n1 | tr -s ',' '\n' | while read -r BIN_NAME BIN_PATH; do
+      # filter empty entries / empty "lines"
+      if [[ -z "$BIN_NAME" ]]; then
+           continue
+      fi
+
+      if [[ -z "$BIN_PATH" ]]; then
+        # heuristic to "guess" the correct source file as found in cargo:
+        # https://github.com/rust-lang/cargo/blob/90fc9f620190d5fa3c80b0c8c65a1e1361e6b8ae/src/cargo/util/toml/targets.rs#L308-L325
+
+        # the first two cases are the "new" default IIRC
+        BIN_NAME_=$(echo $BIN_NAME | sed -e 's/-/_/g')
+        FILES="src/bin/$BIN_NAME_.rs src/bin/$BIN_NAME_/main.rs src/bin/main.rs src/main.rs"
+
+        if ! [ -e "${libPath}" -o -e src/lib.rs -o -e "src/${libName}.rs" ]; then
+          # if this is not a library the following path is also valid
+          FILES="src/$BIN_NAME_.rs $FILES"
+        fi
+
+        echo $FILES
+        for file in $FILES;
+        do
+          echo "checking file $file"
+          # first file that exists wins
+          if [[ -e "$file" ]]; then
+                  BIN_PATH="$file"
+                  break
+          fi
+        done
+
+        if [[ -z "$BIN_PATH" ]]; then
+          echo "failed to find file for binary target: $BIN_NAME" >&2
+          exit 1
+        fi
+      fi
+      build_bin $BIN_NAME $BIN_PATH
+    done
+
+
+    ${lib.optionalString (crateBin == "") ''
+      if [[ -e src/main.rs ]]; then
+        build_bin ${crateName} src/main.rs
+      fi
+      for i in src/bin/*.rs; do #*/
+        build_bin "$(basename $i .rs)" "$i"
+      done
+    ''}
+    # Remove object files to avoid "wrong ELF type"
+    find target -type f -name "*.o" -print0 | xargs -0 rm -f
+  '' + finalBins + ''
+    runHook postBuild
+  ''