Define a custom CI and add docs for the downstream toolchain

This change also updates the changelog, README (and related files) etc.

The custom CI is authored by Anton Baliasnikov <aba@matterlabs.dev> and the rest
is authored by Oleksandr Zarudnyi <hedgar2017@gmail.com>.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -1,46 +1,39 @@
 ---
-name: Bug Report
-about: Problems, deficiencies, inaccuracies or crashes discovered on Solidity.
+name: Bug report
+about: Use this template for reporting issues
 title: ''
-labels: 'bug :bug:'
+labels: bug
 assignees: ''
-
 ---
 
-<!--## Prerequisites
+### 🐛 Bug Report
+
+#### 📝 Description
+
+Provide a clear and concise description of the bug.
+
+#### 🔄 Reproduction Steps
 
-- First, many thanks for taking part in the community. We really appreciate that.
-- We realize there is a lot of information requested here. We ask only that you do your best to provide as much information as possible so we can better help you.
-- Support questions are better asked in one of the following locations:
-    - [Solidity chat](https://gitter.im/ethereum/solidity)
-    - [Stack Overflow](https://ethereum.stackexchange.com/)
-- Ensure the issue isn't already reported.
-- The issue should be reproducible with the latest solidity version; however, this isn't a hard requirement and being reproducible with an older version is sufficient.
+Steps to reproduce the behaviour
 
-*Delete the above section and the instructions in the sections below before submitting*
--->
+#### 🤔 Expected Behavior
 
-## Description
+Describe what you expected to happen.
 
-<!--Please shortly describe the bug you have found, and what you expect instead.-->
+#### 😯 Current Behavior
 
-## Environment
+Describe what actually happened.
 
-- Compiler version:
-- Target EVM version (as per compiler settings):
-- Framework/IDE (e.g. Truffle or Remix):
-- EVM execution environment / backend / blockchain client:
-- Operating system:
+#### 🖥️ Environment
 
-## Steps to Reproduce
+Any relevant environment details.
 
-<!--
-Please provide a *minimal* source code example to trigger the bug you have found.
-Please also mention any command-line flags that are necessary for triggering the bug.
-Provide as much information as necessary to reproduce the bug.
+#### 📋 Additional Context
 
-```solidity
-// Some *minimal* Solidity source code to reproduce the bug.
-// ...
+Add any other context about the problem here. If applicable, add screenshots to help explain.
+
+#### 📎 Log Output
+
+```
+Paste any relevant log output here.
 ```
--->

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,43 +1,21 @@
 ---
-name: Feature Request
-about: Ideas, comments or messages asking for a particular functionality to be added
-  to Solidity.
+name: Feature request
+about: Use this template for requesting features
 title: ''
-labels: feature
+labels: feat
 assignees: ''
-
 ---
 
-<!--## Prerequisites
-
-- First, many thanks for taking part in the community. We really appreciate that.
-- We realize there is a lot of data requested here. We ask only that you do your best to provide as much information as possible so we can better help you.
-- Support questions are better asked in one of the following locations:
-    - [Solidity chat](https://gitter.im/ethereum/solidity)
-    - [Stack Overflow](https://ethereum.stackexchange.com/)
-- Ensure the issue isn't already reported (check `feature` and `language design` labels).
-- If you feel uncertain about your feature request, perhaps it's better to open a language design or feedback forum thread via the issue selector, or by going to the forum directly.
-    - [Solidity forum](https://forum.soliditylang.org/)
-
-*Delete the above section and the instructions in the sections below before submitting*
--->
-
-## Abstract
-
-<!--Please describe by example what problem you see in the current Solidity language and reason about it.-->
-
-## Motivation
+### 🌟 Feature Request
 
-<!--In this section you describe how you propose to address the problem you described earlier, including by giving one or more exemplary source code snippets for demonstration.-->
+#### 📝 Description
 
-## Specification
+Provide a clear and concise description of the feature you'd like to see.
 
-<!--The technical specification should describe the syntax and semantics of any new feature. The specification should be detailed enough to allow any developer to implement the functionality.-->
+#### 🤔 Rationale
 
-## Backwards Compatibility
+Explain why this feature is important and how it benefits the project.
 
-<!--
-All language changes that introduce backwards incompatibilities must include a section describing these incompatibilities and their severity.
+#### 📋 Additional Context
 
-Please describe how you propose to deal with these incompatibilities.
--->
+Add any other context or information about the feature request here.

.github/actions/solc-build/action.yml

@@ -0,0 +1,110 @@
+name: 'Build'
+description: 'Builds solc executable.'
+inputs:
+  release-suffix:
+    description: 'Release suffix.'
+    required: false
+    default: ''
+  zksync-version:
+    description: 'Release version.'
+    required: true
+  solc-version:
+    description: 'Solidity version.'
+    required: true
+  build-type:
+    description: 'Build type: candidate or reference'
+    required: false
+    default: 'candidate'
+  extra-args:
+    description: 'Extra arguments for cmake.'
+    required: false
+    default: ''
+runs:
+  using: "composite"
+  steps:
+
+    - name: Install Boost (MacOS and Linux)
+      if: runner.os != 'Windows'
+      shell: bash
+      env:
+        BOOST_DOWNLOAD_URL: "https://boostorg.jfrog.io/artifactory/main/release/1.83.0/source"
+        BOOST_FILENAME: "boost_1_83_0"
+      run: |
+        [ ${RUNNER_OS} = macOS ] && PARALLEL=$(sysctl -n hw.ncpu) || PARALLEL=$(nproc)
+        curl -L -o ${BOOST_FILENAME}.tar.gz "${BOOST_DOWNLOAD_URL}/${BOOST_FILENAME}.tar.gz"
+        tar xzf "${BOOST_FILENAME}.tar.gz" && cd ${BOOST_FILENAME}
+        if [ ${RUNNER_OS} = macOS ]; then
+          if [ ${RUNNER_ARCH} = X64 ]; then
+            ./bootstrap.sh --prefix=${PWD}/boost --with-python-version=2.7
+          else
+            ./bootstrap.sh --prefix=${PWD}/boost
+          fi
+        else
+          ./bootstrap.sh --prefix=/boost
+        fi
+        ./b2 link=static runtime-link=static -j${PARALLEL}
+        ./b2 install -j${PARALLEL}
+
+    - name: Build solc
+      shell: ${{ runner.os == 'Windows' && 'msys2 {0}' || 'bash' }}
+      env:
+        CXXFLAGS: "-Wno-narrowing"
+      run: |
+        set -x
+        mkdir -p ./build
+        cd ./build
+        [ ${RUNNER_OS} = macOS ] && PARALLEL=$(sysctl -n hw.ncpu) || PARALLEL=$(nproc)
+        if [ ${RUNNER_OS} != Windows ]; then
+          export BOOST_ROOT=/boost
+        fi
+        if [ ${RUNNER_OS} = Linux ]; then
+          COMPILER_FLAGS="-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++"
+        fi
+        if [ ${RUNNER_OS} = Windows ]; then
+           COMPILER_FLAGS="-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_CXX_FLAGS=-fuse-ld=lld -DUSE_LD_GOLD=OFF"
+           export LDFLAGS='-lbcrypt -lwsock32 -static'
+        fi
+        cmake .. \
+          -DCMAKE_BUILD_TYPE="Release" ${COMPILER_FLAGS} \
+          -DSOL_VERSION_ZKSYNC="${{ inputs.solc-version }}-${{ inputs.zksync-version }}" \
+          -DSOLC_VERSION_ZKEVM="${{ inputs.solc-version }}-${{ inputs.zksync-version }}" \
+          -DSOL_VERSION_ZKEVM="${{ inputs.solc-version }}-${{ inputs.zksync-version }}" \
+          -DUSE_Z3=OFF \
+          -DUSE_CVC4=OFF \
+          -DTESTS=0 \
+          -DBoost_NO_BOOST_CMAKE=TRUE \
+          -DSOLC_LINK_STATIC=1 \
+          -DSTATIC_LINKING=1 \
+          -DPEDANTIC=OFF ${{ inputs.extra-args}}
+        if [[ ${{ inputs.solc-version}} == "0.4"* ]]; then
+          cmake --build . --config Release --parallel ${PARALLEL} --target jsoncpp-project
+          cmake --build . --config Release --parallel ${PARALLEL} --target range-v3-project
+        fi
+        cmake --build . --config Release --parallel ${PARALLEL} --target solc
+        [ "$RUNNER_OS" = "Windows" ] && WIN_SUFFIX=".exe"
+        cp ./solc/solc${WIN_SUFFIX} ./solc/solc-${{ inputs.solc-version }}-${{ inputs.build-type }}${WIN_SUFFIX}
+
+    - name: Upload binary for testing
+      if: inputs.release-suffix == ''
+      uses: actions/upload-artifact@v4
+      with:
+        name: solc-${{ inputs.solc-version }}-${{ inputs.build-type }}
+        path: ./build/solc/solc-${{ inputs.solc-version }}-${{ inputs.build-type }}
+
+    - name: Prepare binary
+      if: inputs.release-suffix != ''
+      shell: ${{ runner.os == 'Windows' && 'msys2 {0}' || 'bash' }}
+      run: |
+        [ "$RUNNER_OS" = "Windows" ] && WIN_SUFFIX=".exe"
+        SOLC_BIN="./build/solc/solc${WIN_SUFFIX}"
+        mkdir -p ./releases/${{ inputs.release-suffix }}
+        strip "${SOLC_BIN}"
+        ${SOLC_BIN} --version
+        mv ${SOLC_BIN} ./releases/${{ inputs.release-suffix }}/solc-${{ inputs.release-suffix }}-${{ inputs.solc-version}}-${{ inputs.zksync-version }}${WIN_SUFFIX}
+
+    - name: Upload binary for release
+      if: inputs.release-suffix != ''
+      uses: actions/upload-artifact@v4
+      with:
+        name: release-${{ inputs.release-suffix }}
+        path: releases

.github/pull_request_template.md

@@ -0,0 +1,19 @@
+# What ❔
+
+<!-- What are the changes this PR brings about? -->
+<!-- Example: This PR adds a PR template to the repo. -->
+<!-- (For bigger PRs adding more context is appreciated) -->
+
+## Why ❔
+
+<!-- Why are these changes done? What goal do they contribute to? What are the principles behind them? -->
+<!-- Example: PR templates ensure PR reviewers, observers, and future iterators are in context about the evolution of repos. -->
+
+## Checklist
+
+<!-- Check your PR fulfills the following items. -->
+<!-- For draft PRs check the boxes as you complete them. -->
+
+- [ ] PR title corresponds to the body of PR (we generate changelog entries from PRs).
+- [ ] Tests for the changes have been added / updated.
+- [ ] Documentation comments have been added / updated.