Only install curl (and gnupg for the 18.04 slim image) for the last build step. Caching works much better that way.

Author: gwynne

5.1/ubuntu/16.04/Dockerfile

@@ -17,7 +17,6 @@ RUN export DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true && ap
     tzdata \
     git \
     pkg-config \
-    curl \
     && rm -r /var/lib/apt/lists/*
 
 # Everything up to here should cache nicely between Swift versions, assuming dev dependencies change little
@@ -41,6 +40,9 @@ RUN set -e; \
     SWIFT_WEBDIR="$SWIFT_WEBROOT/$SWIFT_BRANCH/$(echo $SWIFT_PLATFORM | tr -d .)/" \
     && SWIFT_BIN_URL="$SWIFT_WEBDIR/$SWIFT_VERSION/$SWIFT_VERSION-$SWIFT_PLATFORM.tar.gz" \
     && SWIFT_SIG_URL="$SWIFT_BIN_URL.sig" \
+    # - Grab curl here so we cache better up above
+    && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -q update && apt-get -q install -y curl && rm -rf /var/lib/apt/lists/* \
     # - Download the GPG keys, Swift toolchain, and toolchain signature, and verify.
     && export GNUPGHOME="$(mktemp -d)" \
     && curl -fsSL "$SWIFT_BIN_URL" -o swift.tar.gz "$SWIFT_SIG_URL" -o swift.tar.gz.sig \

5.1/ubuntu/16.04/slim/Dockerfile

@@ -8,7 +8,6 @@ RUN export DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true && ap
     libcurl3 \
     libxml2 \
     tzdata \
-    curl \
     && rm -r /var/lib/apt/lists/*
 
 # Everything up to here should cache nicely between Swift versions, assuming dev dependencies change little
@@ -32,6 +31,9 @@ RUN set -e; \
     SWIFT_WEBDIR="$SWIFT_WEBROOT/$SWIFT_BRANCH/$(echo $SWIFT_PLATFORM | tr -d .)/" \
     && SWIFT_BIN_URL="$SWIFT_WEBDIR/$SWIFT_VERSION/$SWIFT_VERSION-$SWIFT_PLATFORM.tar.gz" \
     && SWIFT_SIG_URL="$SWIFT_BIN_URL.sig" \
+    # - Grab curl here so we cache better up above
+    && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -q update && apt-get -q install -y curl && rm -rf /var/lib/apt/lists/* \
     # - Download the GPG keys, Swift toolchain, and toolchain signature, and verify.
     && export GNUPGHOME="$(mktemp -d)" \
     && curl -fsSL "$SWIFT_BIN_URL" -o swift.tar.gz "$SWIFT_SIG_URL" -o swift.tar.gz.sig \

5.1/ubuntu/18.04/Dockerfile

@@ -17,7 +17,6 @@ RUN export DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true && ap
     tzdata \
     git \
     pkg-config \
-    curl \
     && rm -r /var/lib/apt/lists/*
 
 # Everything up to here should cache nicely between Swift versions, assuming dev dependencies change little
@@ -41,6 +40,9 @@ RUN set -e; \
     SWIFT_WEBDIR="$SWIFT_WEBROOT/$SWIFT_BRANCH/$(echo $SWIFT_PLATFORM | tr -d .)/" \
     && SWIFT_BIN_URL="$SWIFT_WEBDIR/$SWIFT_VERSION/$SWIFT_VERSION-$SWIFT_PLATFORM.tar.gz" \
     && SWIFT_SIG_URL="$SWIFT_BIN_URL.sig" \
+    # - Grab curl here so we cache better up above
+    && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -q update && apt-get -q install -y curl && rm -rf /var/lib/apt/lists/* \
     # - Download the GPG keys, Swift toolchain, and toolchain signature, and verify.
     && export GNUPGHOME="$(mktemp -d)" \
     && curl -fsSL "$SWIFT_BIN_URL" -o swift.tar.gz "$SWIFT_SIG_URL" -o swift.tar.gz.sig \

5.1/ubuntu/18.04/slim/Dockerfile

@@ -8,8 +8,6 @@ RUN export DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true && ap
     libcurl4 \
     libxml2 \
     tzdata \
-    curl \
-    gnupg \
     && rm -r /var/lib/apt/lists/*
 
 # Everything up to here should cache nicely between Swift versions, assuming dev dependencies change little
@@ -33,6 +31,9 @@ RUN set -e; \
     SWIFT_WEBDIR="$SWIFT_WEBROOT/$SWIFT_BRANCH/$(echo $SWIFT_PLATFORM | tr -d .)/" \
     && SWIFT_BIN_URL="$SWIFT_WEBDIR/$SWIFT_VERSION/$SWIFT_VERSION-$SWIFT_PLATFORM.tar.gz" \
     && SWIFT_SIG_URL="$SWIFT_BIN_URL.sig" \
+    # - Grab curl and gpg here so we cache better up above
+    && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -q update && apt-get -q install -y curl gnupg && rm -rf /var/lib/apt/lists/* \
     # - Download the GPG keys, Swift toolchain, and toolchain signature, and verify.
     && export GNUPGHOME="$(mktemp -d)" \
     && curl -fsSL "$SWIFT_BIN_URL" -o swift.tar.gz "$SWIFT_SIG_URL" -o swift.tar.gz.sig \