Revert "Require Go >= 1.16."

Running test and vet with Go 1.17 has uncovered some issues, which breaks CI.
This change will be rolled forward after I have a local Go 1.17 environment and
fix those issues.

This reverts commit 9afb84e4fd586a7d34ad3a91831826b2dee71f80.

.github/workflows/ci.yml

@@ -16,11 +16,11 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu, macos, windows]
-        go-version: [1.17.x]
+        go-version: [1.16.x]
         include:
           # Test old supported Go version
           - os: ubuntu
-            go-version: 1.16.x
+            go-version: 1.15.x
     env:
       ELVISH_TEST_TIME_SCALE: 20
     runs-on: ${{ matrix.os }}-latest
@@ -51,10 +51,10 @@ jobs:
       if: matrix.os == 'ubuntu'
       run: echo ostype=linux >> $GITHUB_ENV
     - name: Generate test coverage
-      if: matrix.go-version == '1.17.x'
+      if: matrix.go-version == '1.16.x'
       run: go test -coverprofile=cover -coverpkg=./pkg/... ./pkg/...
     - name: Save test coverage
-      if: matrix.go-version == '1.17.x'
+      if: matrix.go-version == '1.16.x'
       uses: actions/upload-artifact@v2
       with:
         name: cover-${{ env.ostype }}
@@ -72,7 +72,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.17.x
+        go-version: 1.16.x
     - name: Run benchmarks
       run: go test -bench=. -run='^$' ./...
 
@@ -108,12 +108,12 @@ jobs:
         path: |
           ~/go/pkg/mod
           ~/.cache/go-build
-        key: buildall/${{ matrix.os }}/1.17.x/${{ hashFiles('go.sum') }}/${{ github.sha }}
-        restore-keys: buildall/${{ matrix.os }}/1.17.x/${{ hashFiles('go.sum') }}
+        key: buildall/${{ matrix.os }}/1.16.x/${{ hashFiles('go.sum') }}/${{ github.sha }}
+        restore-keys: buildall/${{ matrix.os }}/1.16.x/${{ hashFiles('go.sum') }}
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.17.x
+        go-version: 1.16.x
     - name: Build binaries
       # TODO: Use PR number for suffix when running for PR
       run: ELVISH_REPRODUCIBLE=dev ./tools/buildall.sh . bin HEAD
@@ -132,7 +132,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.17.x
+        go-version: 1.16.x
     - name: Set up goimports
       run: go install golang.org/x/tools/cmd/goimports@latest
     - name: Check style
@@ -179,7 +179,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.17.x
+        go-version: 1.16.x
     - name: Set up staticcheck
       run: go install honnef.co/go/tools/cmd/staticcheck@2021.1
     - name: Run linters

README.md

@@ -38,7 +38,7 @@ To build Elvish from source, you need
 
     **NOTE**: Windows 10 support is experimental.
 
--   Go >= 1.16.
+-   Go >= 1.15.
 
 To build Elvish from source, follow these steps:
 

go.mod

@@ -7,4 +7,4 @@ require (
 	golang.org/x/sys v0.0.0-20200824131525-c12d262b63d8
 )
 
-go 1.16
+go 1.15

website/go.mod

@@ -1,6 +1,6 @@
 module src.elv.sh/website
 
-go 1.16
+go 1.15
 
 require (
 	github.com/BurntSushi/toml v0.3.1